Road Race Wheels Cerca 1986

[Hindmost]

Set the Wayback Machine Sherman:

Say I was building road race wheels for Colombian climbers to use in a professional, three week stage race in France. What spokes and lacing would I use?

Also, I could use suggestions for spokes that are still currently available.

[ultraman6970]

Back in the day everybody was doing the same thing and way simpler than now a days because there was nothing weird in the market.

32 or 36 spokes 3x, box tubular rims. Simple and worked.

By mid 90s weird stuff started showing up, including campagnolo and mavic wheelsets, but you are taking about before than that, then 3x tubular rims with 32 or 36 holes in 3x pattern.

For TT they were going to 28 or 24, but those wheels were built just to last those races, 24 and 28 spokes rims back in the day were really flimsy.

Spokes hmm... many guys were using alpina and dt, you might find union but I would not even put a wheel together with those... no idea when sapim started so no idea if they were around back then, but alpina was there already, one of the 1st ones to make kind'a aero spokes.

[likebikes]

i have a staggered set in the basement, chorus FW hubs laced to a v-section mavic rim for the rear, and a box section for the front. tubular of course!

[ultraman6970]

Racing wheels = tubulars back then...

Now a days everybody use clinchers for racing amateur, pro from looking at the wheels they go tubular but maybe that super fast TT clincher that spech created? doubt i will try that ever so cant tell you if their mythical numbers are real or not.

[jumphigher]

Dont mean to hijack the thread but.. why are modern wheels so much stronger - what has changed?

[ultraman6970]

The shape of the rims changed, that makes a lot of difference, same with the alumunim used for those rims. U go from box to a 30 mm rim that uses shorter spokes you end up with a stiffer wheel, thats why you can see stupidly low spoke wheels now a days. Do 24 spokes in a 40 year old box tubular rims and that thing will be like jelly (this is when sombody will add about tie the spokes together, well u want stiffer you had to tie them), and probably wont last too long either thats why were used only in TT races where weight was the key factor.

Even now a days some low spoke wheels you can tell the rim is moving from side to side in the curves, where is more noticeable.

Now a days with carbon rims the thing changed everything, they can play better with the layout of the carbon layers plus the height of the rim, which result in less spokes, lighter and stiffer wheel.

[m_sasso]

3 cross, Sapim Race Spokes, Silver, DB, 2.0 – 1.8 – 2.0 is what I would use currently.

In those days likely West German, Berg Union or DT Swiss with 12mm brass nipples, 3 cross.

[oldpotatoe]

Set the Wayback Machine Sherman:

Say I was building road race wheels for Colombian climbers to use in a professional, three week stage race in France. What spokes and lacing would I use?

Also, I could use suggestions for spokes that are still currently available.

‘To finish first you have to first finish’....32, 3 cross, double butted spokes in 2mm-1.8mm-2mm on tubular, box section rims, Mavic, Campagnolo, FIR, Ambrosio.. DT or Sapim spokes, brass nipps. ‘Maybe’ 28h fronts for climbing days altho weight diff way small(about 30grams)...

[Kontact]

Of the "normal" wheels of the time (rather than something like Rovals or weirder), the more cutting edge wheels might have butted spokes and be 28 fronts with 32 rears on something like GP4 rims. Matched 28/32 hubsets were not uncommon in the early '80s. I also would not be surprised to see 15 gauge straight spokes.

I built a 28/28 wheelset a few years ago with 15 gauge spokes - they've held up well.

[jumphigher]

The shape of the rims changed, that makes a lot of difference, same with the alumunim used for those rims. U go from box to a 30 mm rim that uses shorter spokes you end up with a stiffer wheel, thats why you can see stupidly low spoke wheels now a days. Do 24 spokes in a 40 year old box tubular rims and that thing will be like jelly (this is when sombody will add about tie the spokes together, well u want stiffer you had to tie them), and probably wont last too long either thats why were used only in TT races where weight was the key factor.

Even now a days some low spoke wheels you can tell the rim is moving from side to side in the curves, where is more noticeable.

Now a days with carbon rims the thing changed everything, they can play better with the layout of the carbon layers plus the height of the rim, which result in less spokes, lighter and stiffer wheel.

Thanks for that info. I had wondered how such low spoke counts are now commonplace. :)

[Kontact]

Thanks for that info. I had wondered how such low spoke counts are now commonplace. :)

Low spoke counts started with alloy Roval wheels, long before carbon rims.

[Hindmost]

Dont mean to hijack the thread but.. why are modern wheels so much stronger - what has changed?

One word: Extrusion. Another Paceliner once pointed out that prior to this, aluminum rims were essentially rolled sheet, welded into seamed tubing, then shaped into rims. The aluminum had to be soft enough for the shaping to occur. Low spoke count wheels were not an option with the resulting rims..

[choke]

Low spoke counts started with alloy Roval wheels, long before carbon rims.Yep.....

http://velobase.com/ViewComponent.aspx?ID=583e94cc-04b6-47cd-b280-9a4421f12d07

http://www.classicrendezvous.com/France/parts/Roval.htm

[Chris]

My first real race bike was built in ‘86. The sponsor built me a set of race wheels that was record hubs and gp4 rims. Tubies glued with Fastac.

[ultraman6970]

Technology changed a lot in the last 25 years in wheels, the thing was pretty much stuck since the beginning of times, the technology was not there yet.

Remember when the 1st aero rims came up, I believe saavedra was one of the 1st ones if not the 1st one, Argentinian made, really nice finish... got my TT wheels for the track built with those, 28h... had one problem with them, creaked like crazy in the banks. Never dare to even use them as spare wheels for points races because those rims were not going to hold and end up cracking. Never tried other aero profile rims till I was able to put my hands in campagnolo and mavic ones and from touching the rim you were able to tell the aluminum was different, but campagnolo and mavic came up with their aero profile rims maybe 5 years after than saavedra. So clearly technology and metallurgic advances helped a lot to get stupid low spoke wheels now a days.

[Gummee]

My first real race bike was built in ‘86. The sponsor built me a set of race wheels that was record hubs and gp4 rims. Tubies glued with Fastac.

Man did I love Fastac!

Re the OP: GEL 280 front, GL330 rear. 32/32 Unless the guy racing the wheels was tiny, then a pair of GEL280s

M

[John H.]

FIR Pulsar box section 32 hole.
2x14-15 front with alloy nips.
3x14-15 rear with brass nips on drive side.
Mavic hubs-

[bikinchris]

Also Galli and Assos rims.

[bikinchris]

Man did I love Fastac!

Re the OP: GEL 280 front, GL330 rear. 32/32 Unless the guy racing the wheels was tiny, then a pair of GEL280s

M

Early in my career, I built sets of wheels for a pair of twin 13 year old girls to race:
28 hole GEL 280 fronts with Titanium spokes and 32 hole GEL 330 rears with DT Revolution (or some other super light steel spoke) on Record hubs with Ti axles.
I wouldn't even test ride bikes with those wheels, since I weighed more than both of the girls added together.

[carpediemracing]

Dont mean to hijack the thread but.. why are modern wheels so much stronger - what has changed?

I didn't read through all the answers but the short answer: stronger rims.

Back in the day I used to run 280g rim tubulars, which were probably 300-330g actual weight, but still, very light. Nowadays you won't find many rims like that in aluminum (any?) and "light" rims are 400-450g, which was as heavy as they got back then.

Such rims required a higher minimum number of spokes because the spokes were an integral part of the load rating.

However, with a heavier rim, the spokes do less weight bearing work and really just position the hub within the rim. With a 280g rim if you sat hard on an unlaced rim you'd bend it. With a 400g rim, less of a chance, and, nowadays, a 450g carbon rim can support quite a bit of weight without being laced. Heavier/stronger rims no longer needed the spokes to help support the weight, so you could find some crazy low spoke counts (down to 12 spokes for the aluminum Shamals, which weighed a lot in order to be strong enough), and even now you'll see 18 spoke front wheels (HED Ardennes type rim, of which I have a couple).

[Kontact]

Here's a shot from the '86 TDF. Hinnault's front wheel is clearly a 28 spoke. I can't see his rear well enough to say.

http://coresites-cdn.factorymedia.com/rcuk/wp-content/uploads/2016/07/Greg-LeMond-Bernard-Hinault-Alpe-dHuez-1986-Tour-de-France-pic-Sirotti.jpg


One word: Extrusion. Another Paceliner once pointed out that prior to this, aluminum rims were essentially rolled sheet, welded into seamed tubing, then shaped into rims. The aluminum had to be soft enough for the shaping to occur. Low spoke count wheels were not an option with the resulting rims.

That happened a lot longer ago than 1986. All alloy clinchers are extrusions, for instance.

[carpediemracing]

My first set of race wheels (only wheels on my first ever serious bike) was a set of Campy Tipos with GP4s, 32H. Huge overkill on strength - I still have the front wheel, with 31 spokes (I rode it like that for years), somewhere in the garage.

My "best" race wheels in the 1990s were 28H Campy Record Crono rims, NR hubs, 1.8mm DB spokes. I still have a front wheel but the rears were a bit fragile, especially since one of my favorite tactics in a crit was to bomb through potholes/manhole-covers/sewer-grates since no one else wanted to go through them. The Record Crono rims were much rounder out of the box than any GEL280 I ever had so therefore had much more even spoke tension. For myself and through the shop I probably built 10 pairs of Record Cronos, maybe more, and maybe 4-6 sets of GEL280s.

My strongest "good" wheels were 28H FiR Isidis / whatever hub wheels I used Kingsberry and American Classic hubs, typically, and 1.8mm DB spokes up front, 1.8mm DB NDS / 2.0 DB DS in the rear.

I started converting to Zipp 340 rims, 24H Campy Record hubs, at about that time, and so the front wheels remained for hilly races (which I still did, now and then) for the fast descents. Otherwise I used Specialized Trispokes, Zipp 340/440s, Spinergys, and a proto rear disk wheel, depending on the course and my mood.

[jumphigher]

Thanks to everyone commenting on my 'why are modern wheels stronger?" question. I've learned a lot. :)

[tv_vt]

Another rim brand from those days: Nisi. Think they had an 'aero' V shaped rim, too. Wolber was around then also.

[bikinchris]

Yes, I should have remembered Wolber. I liked the look of the big white decals on the dark anodizing.

Low priced builds often had Matrix rims from Trek.

[Hindmost]

These are my time trial wheels I built and raced 30 years ago. GL 330's 32 3x. Spokes are 1.8/1.6 DT's. I used to weigh 170lbs, or so.

My current Eroica project is to be "Tout Mavic." I was imagining wheels for Lucho Herrera or Fabio Parra and was thinking 32 hole and 1.8/1.6 spokes again.

[oldpotatoe]

Man did I love Fastac!

Re the OP: GEL 280 front, GL330 rear. 32/32 Unless the guy racing the wheels was tiny, then a pair of GEL280s

M

I 'raced' on GEL280F, GL330R, 15/16 spokes, onto Hi-E hubs BUT I was 180 pounds or so so 36h...

[wallymann]

surely the TX profils were amongst the earliest viable aero rims widely available on the market. they were good enough that i still use mine on a regular basis, and they were built new in 1987 -- although have been re-laced to more modern hubs in the last ~5 years: F28(rad) + R32(3x)

https://photos.smugmug.com/Print-Gallery/Badger/i-96RS8GK/0/db39a03d/M/WATSON_TDF_00001575-600-M.jpg

in general, everyone nailed the options back in the '80s for race wheels: some combination of GEL280 - GL330 - GP4 (and equivalents) depending on the duty-cycle of the wheel and the owner's desire for durability vs lightweight-ness.

last year i built up some NOS 32H box-section Sun mistral clinchers on a set of disc hubs w/ 3X lacing for my gravel bike -- they looked the business, but failed miserably. i think the 2 big missing ingredients: lacking a strong cross-section (a-la not v-shaped) and not being heat-treated. even moderate rough roads they'd go massively out of true after one ride.

Another rim brand from those days: Nisi. Think they had an 'aero' V shaped rim, too. Wolber was around then also.

nisi lasers...to die for!

http://velobase.com/CompImages/Rims/0BE4D126-12E4-49A5-BF0B-89A66AC12F7B.jpeg

[Tommasini53]

Your thread brings to point one of the biggest improvements in cycling; light and durable wheelsets.

80's era crits in the midwest were 28h 280gr Mavic rims, 3x, Campy high flange hubs, and Clement Seta Extra tires. Fantastic to ride on but wow, they were not durable. If you didn't dent the rim, a spoke probably pulled an eyelet through the rim. If you raced, you probably knew how to lace and build a wheel (or had a friend that did) because you were building several sets a year.
I'm not riding super light wheels, Campy Eurus, but they are a decade old and potholes and gravel haven't damaged them. great thread. :banana:

[stien]

It's circa not cerca :crap:

[Kontact]

It's circa not cerca :crap:

It's Stien not stien :crap:

[Gummee]

Early in my career, I built sets of wheels for a pair of twin 13 year old girls to race:
28 hole GEL 280 fronts with Titanium spokes and 32 hole GEL 330 rears with DT Revolution on Record hubs with Ti axles.
I wouldn't even test ride bikes with those wheels, since I weighed more than both of the girls added together.

I still have a few pairs of wheels worth of Ti spokes. GL330s and ti spokes were a very interesting ride. Always felt like I had a flat.

Very light tho

Prior to the GL330s, I'd built a few pair of CXP30s with the Ti spokes. I don't remember if they were 24/24 or 24/28. 1st set was raidal NDS in the rear. Felt great going straight ahead, but wonky if you turned one way. ...but not the other!

Sold that wheelset to a triathlete and rebuilt em 2x and they felt as fine as Ti spokes felt.

M

[ultraman6970]

As potato said, if you are racing you need a pair of wheels that can take you to the finish line, that being said... my pick was some like heavy but never had problems even getting flats... 36h 3x gp4 rims.. alpina spokes and campy or shimano hubs, 23 mm tubbies in the road... 22 or 21 in the track and for TT in the track I had 19mm 160 grams tubbies. For TT in the road always played safe...23 or 22 mm. Had wheels built with nisi superwhatever the equivalent of the gp4 in nisi, I still have those rims moving around and still could built a set of wheels with them...

For training I used ambrosio montreal that IMO were in the soft side but were cheap enough to get them replaced often in case of way too many dents :D

[Kontact]

I still have a few pairs of wheels worth of Ti spokes. GL330s and ti spokes were a very interesting ride. Always felt like I had a flat.

...rebuilt em 2x and they felt as fine as Ti spokes felt.


Feeling like you have a flat is "fine"?

I can't tell if you like Ti spokes or not.

[bikinchris]

When you got the Ti spokes tight, they were fine and felt just like stainless spokes. BUT you have to build the wheels, then re-tension them after riding them a while.

[Mark McM]

One word: Extrusion. Another Paceliner once pointed out that prior to this, aluminum rims were essentially rolled sheet, welded into seamed tubing, then shaped into rims. The aluminum had to be soft enough for the shaping to occur. Low spoke count wheels were not an option with the resulting rims..

As you say, a relatively soft aluminum alloy must be used for rims that are formed from sheets. In many instances, the extrusion process actually increases the strength of the aluminum by a form of heat treating - the alloy is first heated to soften it so that it can be pushed through the extrusion die, and then is quenched after it emerges from the die.

But perhaps more importantly, extrusion allows greater control of rim wall thickness - the rim walls can be made thick at the spoke bed and brake tracks, but thin on the rest of the sidewalls, so the rim can be stiffer and stronger at the same weight than a rim made from a (constant thickness) sheet.

[Kontact]

The thing is that extruded rims aren't "modern", so it really isn't a great explanation for the more recent reduction in spoke number.

I'm willing to bet if you found a mid-'80s Matric ISO aero 36H rim and laced it to an 18H hub, it would hold up no different than a "modern" rim.

[Mark McM]

I didn't read through all the answers but the short answer: stronger rims.

Back in the day I used to run 280g rim tubulars, which were probably 300-330g actual weight, but still, very light. Nowadays you won't find many rims like that in aluminum (any?) and "light" rims are 400-450g, which was as heavy as they got back then.

Such rims required a higher minimum number of spokes because the spokes were an integral part of the load rating.

As you say, lightweight rims are not a modern innovation, there were plenty of lightweight rims back in the day. The GEL280 rims mentioned several times here were light, but they weren't the lightest. I've got an old pair of Weyless rims that are about 215 grams each. I've also got a few Super Champion rims that are about 260-280 grams. And one of the first "aero" rims, the Saavedra Turbo rims (also mentioned elsewhere) had an actual weight of about 280 grams. All tubulars, of course. As also mentioned already, what is a new innovation is lightweight rims that are also reasonably durable.

As you say, these very light rims did require many spokes to avoid very flexy wheels, and to get even a minimal amount of durability. 36 spokes was the norm for these very light rims - 32 spokes was reserved for medium weight rims.

However, with a heavier rim, the spokes do less weight bearing work and really just position the hub within the rim. With a 280g rim if you sat hard on an unlaced rim you'd bend it. With a 400g rim, less of a chance, and, nowadays, a 450g carbon rim can support quite a bit of weight without being laced. Heavier/stronger rims no longer needed the spokes to help support the weight, so you could find some crazy low spoke counts (down to 12 spokes for the aluminum Shamals, which weighed a lot in order to be strong enough), and even now you'll see 18 spoke front wheels (HED Ardennes type rim, of which I have a couple).

These comments seem to echo some of the misconceptions about how wheels work, especially the comment that "Heavier/stronger rims no longer needed the spokes to help support the weight." Clearly, a rim can not support weight without spokes - since the spokes are the only connection between the rim and the hub, the spokes always bear the entire load.

The wheel is a classic pre-stressed structure. At any time, only a few spokes are actually supporting the external load - these spokes are the spokes closest to the ground contact point. The rest of the spokes are there to maintain the pre-tension on the load supporting spokes. The role of rim stiffness is that a stiffer rim distributes loads over a wider area, thus allowing the spokes to be further apart and still have the same number of spokes bearing the load. And spokes being further apart means fewer total spokes. So modern wheels can have fewer spokes not because the rim is stronger, but because the rim is stiffer.

[pbarry]

I brought "good used rims" to Peter a few years ago to lace to 9 speed Campy hubs. Weighed the GEL 280 for the front, and the GEL 330 for the rear. Both came in at 330g. There may have been some optimistic marketing going on back in the day. ;)
That wheelset is one of favorites, despite the rim being 50g over advertised weight..

[Mark McM]

The thing is that extruded rims aren't "modern", so it really isn't a great explanation for the more recent reduction in spoke number.

I'm willing to bet if you found a mid-'80s Matric ISO aero 36H rim and laced it to an 18H hub, it would hold up no different than a "modern" rim.

Extrusion is fine way to make a rim, but older extrusion processes had a harder time maintaining consistancy with very thin walls. So many of the earlier ultra-light rims (less than 400 grams, such as the GEL280 & GL330) were made from forming from sheets, and extrusions were used for heavier rims. This started changing by the late '80s.

Another change was advancements in rolling. Rims are made by forming straight tubes or extrusions, and then bending (rolling) them into a hoop. The deeper the cross section, the more likely it is to distort when rolling into a hoop - this is especially true if the rim has thin walls. This is why the very lightest rims were also quite shallow. Improvements in rolling technology has allowed deeper cross section rims to be made (although 40 mm is still about the maximum feasible limit, and most alloy rims today are typically 30 mm or less).

As has been mentioned, the recent reduction in spoke count isn't all that recent, as 24 spoke wheels were available since the '70s. I suspect that one of the reasons that not many rims were available in low spoke count in the '80s is several fold: Since the bicycle industry can often be quite conservative, and since 32 and 36 spoke wheels were the norm, manufacturers (and wheel builders) were not ready to jump to lower spoke counts. Plus, since 32 and 36 spoke wheels were the norm, there just weren't many low spoke count hubs avaible. When I built my first 24 spoke wheels, there weren't many rims and hubs widely available.

But as you say, if an '80s rim with a similar cross section and depth as modern rims was used, you could likely use the same reduced spoke count as is common on similar rims today.

[Kontact]

The wheel is a classic pre-stressed structure. At any time, only a few spokes are actually supporting the external load - these spokes are the spokes closest to the ground contact point. The rest of the spokes are there to maintain the pre-tension on the load supporting spokes. The role of rim stiffness is that a stiffer rim distributes loads over a wider area, thus allowing the spokes to be further apart and still have the same number of spokes bearing the load. And spokes being further apart means fewer total spokes. So modern wheels can have fewer spokes not because the rim is stronger, but because the rim is stiffer.

I can't see how this could be true. The hub isn't sitting on top of few spokes, it is dangling from the ones above it. If anything, the spokes connected to where the rim touches the ground have the least load on them because the pressure from the ground decreases the pre-tension on those spokes.

[Tandem Rider]

I had a 24 spoke TT front wheel back in the late 80's, Araya rim if I recall. It was a noodle, don't corner hard, it'll raise your heart rate. I'm pretty hard on wheels but I was only 145lbs at the time and it needed truing pretty frequently. I had GP4's for most stuff including training, and GL 330's on 32 spokes for the important races. 2.0-1.8 DT spokes on everything except the TT wheel. It had aero somethings, Alpina maybe. I think I still have a set of 36 hole GP4 wheels that I trained on hanging somewhere. I would go through 6 or 8 racing rims per year, probably 60 or 70 races.

My buddy had a Roval set of wheels, pretty cutting edge and fast. They were the first ones I ever saw like that.

No way would a set of low spoke count wheels hold up on standard 80's rims, I would have pretzeled those on the first ride.

[bikinchris]

I can't see how this could be true. The hub isn't sitting on top of few spokes, it is dangling from the ones above it. If anything, the spokes connected to where the rim touches the ground have the least load on them because the pressure from the ground decreases the pre-tension on those spokes.

The wheel will fail if the spokes it is "standing on" lose tension. So if the sum of the tension of all of the loaded spokes is not higher than the load, then the wheel will taco. More crosses builds a stronger wheel, because the spokes lean on each other so to speak.

[Kontact]

The wheel will fail if the spokes it is "standing on" lose tension. So if the sum of the tension of all of the loaded spokes is not higher than the load, then the wheel will taco. More crosses builds a stronger wheel, because the spokes lean on each other so to speak.

I didn't mean the tension goes to zero. But it has to net decrease from compression. Forces could never remain completely symmetrical.

[El Chaba]

Set the Wayback Machine Sherman:

Say I was building road race wheels for Colombian climbers to use in a professional, three week stage race in France. What spokes and lacing would I use?

Also, I could use suggestions for spokes that are still currently available.

Back to the original post....Many of the Colombian teams were Mavic-sponsored, so I'd start there..

1986 was the 7-speed era for pros, and aerodynamics had come into the consciousness of everybody and had supplanted weightweeniness to a great degree...So...

I would say Mavic SSC hubs, 126 mm spacing. Mavic SSC rims, 28 hole drilling. DT stainless spokes, probably 15g as those light, straight gauge spokes were common then, x2. Maillard 700 freewheel. Vittoria tubulars. Corsa CX for the front, Corsa CG for the rear.

A note on the SSC rims...The pros lucky enough to be sponsored by Mavic almost always got them....Very few non pros would pony up the $100/rim. For regular road race duty, it is the "regular" SSC and not the Pave model...

[oldpotatoe]

It's Stien not stien :crap:

It's weird, not wierd..get it?:)

[Hindmost]

...For regular road race duty, it is the "regular" SSC and not the Pave model...

Thanks for the suggestions. Do you know how the regular SSC's differ from say, the GP4's? The literature usually refers to the Paris-Roubaix model.

[54ny77]

For the mountain goats, GEL 280 w/lovely Vittoria CX sew ups, all on Campy Super Record hubs.

Mmmmmm.....had me a set of those at one point ages ago, oh man were they nice.

Can't remember the lacing, probably 2x front and 3x drive side rear.

Good grief I was a lot lighter then....no way on earth I could even think about using that kind of setup today! :eek:

[shovelhd]

For the mountain goats, GEL 280 w/lovely Vittoria CX sew ups, all on Campy Super Record hubs.

Same here, except I rode Clement silks supplied by the team. These were for smooth roads only (I was 134 pounds). For rough roads, I opted for the same thing with GL330's.

[Mark McM]

I can't see how this could be true. The hub isn't sitting on top of few spokes, it is dangling from the ones above it. If anything, the spokes connected to where the rim touches the ground have the least load on them because the pressure from the ground decreases the pre-tension on those spokes.

The advantage of pre-stressed structures is that it allows structural members to bear loads in ways that they ordinarily would not be able to. For example, standard concrete can't normally bear much bending load, but pre-stressed concrete can, allowing long slender concrete bridge spans to be built.

In the case of the wheels, it can easily be shown that the loads on the wheel are not transferred to the top spokes. If the loads were transferred to the top spokes, you'd expect that the tension in the top spokes would increase when weight was applied to the wheel - but in fact, the tension in the top spokes stays the same under load. Instead, the only spokes with significant changes are the bottom spokes, which bear the load under compression (de-tensioning).

The reason that the loads are not transferred to the top of the wheel has everything to do with the relative stiffnesses of the spokes vs. the rim. The rim is under bending, and so flexes easily under load. But the spokes are very stiff in tension/compression (they retain their compression stiffness as long as they aren't completely de-tensioned). This means that the rim will bend inward under load, and only the bottom spokes will take all the load, with little of the load being transferred else where around the wheel.

This mechanism for how tension spoke wheels bear loads has been known for quite some time. It was first presented in the book, "The Bicycle Wheel" (http://caravan.hobby.ru/materiel/Bicycle_Wheel_-_Jobst_Brandt.pdf) by Jobst Brandt, and been reconfirmed many times. Engineers who studied, modeled and measured the response of wire spoked wheels under load have all reached the same conclusion. Here's a quote from a recent interview on BikeRadar with Keith Bontrager (http://www.bikeradar.com/mtb/gear/article/keith-bontrager-interview-six-things-we-learned-46802/) (of Bontrager wheels) where he discusses this:

KB: If you looked at the change in tension when a load is applied to a wheel, the tension in all the spokes away from the contact-patch area doesn’t change. The weight is not hanging from the spokes. The tension is _reduced_ across the contact patch; the wheel is standing on those spokes. The change in tension is the same as the compressive load. It’s hard to get your head around. It’s a pre-stressed structure, which behaves in ways which aren’t obvious.

[Mark McM]

More crosses builds a stronger wheel, because the spokes lean on each other so to speak.

This has often been hypothesized, but it hasn't actually been demonstrated in practice. In fact, there has been research showing that spoke crossing actually makes little difference in wheel strength/durability. In this study by Henri Gavin (http://people.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf), several otherwise identical wheels but with different numbers of spoke crossings were tested by both static measurement, and by applying strain gauges to spokes and then riding the wheels to measure actual spoke stresses. He found that the number of spoke crossings had little affect on spoke loads. (By the way, Henri Gavin's measurements of wheels under actual riding loads also confirmed the conclusion previously mentioned, that wheels "stand" on their lower spokes.)

[54ny77]

Yup. Them or GP4s for crits "just in case."

What were those red mavic rims? They were the super light things. Very pricey in their day also.

Same here, except I rode Clement silks supplied by the team. These were for smooth roads only (I was 134 pounds). For rough roads, I opted for the same thing with GL330's.

[wallymann]

...This means that the rim will bend inward under load, and only the bottom spokes will take all the load...

doesnt this really mean that the bottom spokes are *unloaded*?

you just said that spokes cannot take much compression, so how can they take any load?

if the rim bends inwards, the bottom spokes yield, meaning that load is taken up by the rest of the spokes that stay in tensions...yes?

[Kontact]

It's weird, not wierd..get it?:)
Not really. :)

[Mark McM]

doesnt this really mean that the bottom spokes are *unloaded*?

That's getting into symantics. It is the bottom spokes that have a stress response to external loads. It is the bottom spokes that can suffer from fatigue (and breakage). Therefore, it is correct to say that the bottom spokes are bearing the load.

you just said that spokes cannot take much compression, so how can they take any load?

As bikinchris said, as long as the bottom spokes have adequate static tension and never completely de-tension, they can bear compressive loading. This, afterall, is the entire purpose of pre-tensioning the spokes - a wheel with inadequate static tension can not bear much load.

if the rim bends inwards, the bottom spokes yield, meaning that load is taken up by the rest of the spokes that stay in tensions...yes?

When we are talking about rim and spoke deflections, keep in mind that the stiffnesses are very high, so the deflections are very small. A typical wheel has a stiffness of about 20,000 lb/in, so under normal loading, the deflection is measured in thousands of an inch.

Also keep in mind that there are typically 3 - 5 spokes in the LAZ (Load Affected Zone) at the bottom of the wheel. If they are each tensioned to 100 kgf, it could take several hundred kgf of load to completey de-tension the spokes.

But as to your original question - yes if the bottom spokes completey de-tensioned, the load will be transferred to other spokes - but at this point, the wheel has been overloaded and has failed. When the bottom spokes become completely un-tensioned, there will be no lateral support of the rim at the bottom, and wheel will become unstable, and easily flex sideways. As this is not a normally functioning wheel, this is not a valid case to model spoke loading.

So, if you want to make sure your wheels "hang from the top spokes", just build them with no static tension - but don't be surprised if the wheels become unrideable. For me, I'll take my wheels with high static tension, so that they "stand on the bottom spokes".

[Kontact]

The advantage of pre-stressed structures is that it allows structural members to bear loads in ways that they ordinarily would not be able to. For example, standard concrete can't normally bear much bending load, but pre-stressed concrete can, allowing long slender concrete bridge spans to be built.

In the case of the wheels, it can easily be shown that the loads on the wheel are not transferred to the top spokes. If the loads were transferred to the top spokes, you'd expect that the tension in the top spokes would increase when weight was applied to the wheel - but in fact, the tension in the top spokes stays the same under load. Instead, the only spokes with significant changes are the bottom spokes, which bear the load under compression (de-tensioning).

The reason that the loads are not transferred to the top of the wheel has everything to do with the relative stiffnesses of the spokes vs. the rim. The rim is under bending, and so flexes easily under load. But the spokes are very stiff in tension/compression (they retain their compression stiffness as long as they aren't completely de-tensioned). This means that the rim will bend inward under load, and only the bottom spokes will take all the load, with little of the load being transferred else where around the wheel.

This mechanism for how tension spoke wheels bear loads has been known for quite some time. It was first presented in the book, "The Bicycle Wheel" (http://caravan.hobby.ru/materiel/Bicycle_Wheel_-_Jobst_Brandt.pdf) by Jobst Brandt, and been reconfirmed many times. Engineers who studied, modeled and measured the response of wire spoked wheels under load have all reached the same conclusion. Here's a quote from a recent interview on BikeRadar with Keith Bontrager (http://www.bikeradar.com/mtb/gear/article/keith-bontrager-interview-six-things-we-learned-46802/) (of Bontrager wheels) where he discusses this:
I didn't mean that the hub was hanging just from the 3 spokes directly above it, but that the hub was suspended and was not supported from the spokes between it and the ground. This is what you said:

At any time, only a few spokes are actually supporting the external load - these spokes are the spokes closest to the ground contact point.

That makes no sense.

As bikinchris said, as long as the bottom spokes have adequate static tension and never completely de-tension, they can bear compressive loading. This, afterall, is the entire purpose of pre-tensioning the spokes - a wheel with inadequate static tension can not bear much load.
You appear to be saying that plum bob string could resist forces pushing up from below if the bob was so heavy to be putting preload on the string. In reality, the spoke and the string have no real rigidity - the only thing supporting the flexible spoke from below is the rim strip. It can't be a compressive structural member if it isn't supported in that direction and has no rigidity.

Under no circumstances do the spokes push out against the rim.

[Mark McM]

That makes no sense.

Please present your arguments against it.

Do you refute that if a spoke is under static tension, that it behaves elastically the same in both tension and compression, as long as it is not completely de-tensioned?

Do you refute that only the bottom spokes have any meaningful changes in stress/strain when the wheel is loaded?

Do you refute that the top spokes in a wheel have no significant change in stress/strain when the wheel is loaded?

If you can not refute any of the above, how can you claim that a wheel load is not supported by the bottom spokes?

(I suspect that you will have a hard time refuting any of these, as they have all been independently verified many times.)

I'll grant that the mechanics of pre-stressed structures are not obvious at first. But if you learn and understand the principles of Superposition of Forces (https://en.wikipedia.org/wiki/Superposition_principle) and Statically Indeterminant Structures (https://en.wikipedia.org/wiki/Statically_indeterminate), you'll understand how the bottom spokes of a tension spoke wheel can (and must) bear the loads.

[Kontact]

Please present your arguments against it.

Do you refute that if a spoke is under static tension, that it behaves elastically the same in both tension and compression, as long as it is not completely de-tensioned?

Do you refute that only the bottom spokes have any meaningful changes in stress/strain when the wheel is loaded?

Do you refute that the top spokes in a wheel have no significant change in stress/strain when the wheel is loaded?

If you can not refute any of the above, how can you claim that a wheel load is not supported by the bottom spokes?

(I suspect that you will have a hard time refuting any of these, as they have all been independently verified many times.)

I'll grant that the mechanics of pre-stressed structures are not obvious at first. But if you learn and understand the principles of Superposition of Forces (https://en.wikipedia.org/wiki/Superposition_principle) and Statically Indeterminant Structures (https://en.wikipedia.org/wiki/Statically_indeterminate), you'll understand how the bottom spokes of a tension spoke wheel can (and must) bear the loads.

The hub is held in space by all the spokes that have tension on it. Mechanically, the only spokes that don't have the same tension are those pointing straight at the ground, because the rim is being pushed out of round across a short section that is directly against the ground. When that happens those spokes fully fully participate in the the suspension of the hub in space.

That's all that is happening.


The bottom spokes have a change in stress/strain because of the unloading/loading cycles, not because they are ever compressed. If you built a wheel and put an enormous load on it without letting it roll, those 2 or 3 spokes on the bottom would simply dangle there as the rest of the spokes snapped under tension. In other words, they aren't under near the load as the other 29 spokes, and only come under great load when the wheel rotates and the rigid structure of the rim is no longer compressed by the contact patch.

I think you've just fooled yourself into thinking that since the top spokes aren't doing all the work, something opposite than must be true. But what is really happening is that the work is evenly distributed to the evenly round shape of the rim, except where the rim's roundness has been mechanically interrupted by the small contact point of the ground.

[Hindmost]

This thread has been a remarkable flashback for me. BITD I lived a 20 minute bike ride from the Old Wheelsmith. Ric and Jon could help you with any question regarding purchase of rims and spokes. Almost anything desired was in stock. They would show you the correct spoke lengths as recorded in their notebook.

On occasion Jobst Brandt would roll in, he lived 5 blocks away, and he would offer an opinion.

[Mark McM]

You appear to be saying that plum bob string could resist forces pushing up from below if the bob was so heavy to be putting preload on the string. In reality, the spoke and the string have no real rigidity - the only thing supporting the flexible spoke from below is the rim strip. It can't be a compressive structural member if it isn't supported in that direction and has no rigidity.

Under no circumstances do the spokes push out against the rim.

This is in correct, and we don't need to look very far from the wheel to find another example of flexible members becoming rigid in pre-stressed structures.

A bicycle tire is made of a flexible fabric casing - it has tensile strength, but no compressive strength. Air is a gas - it doesn't have a distinct shape or volume, let alone any (tensile strength). But when you fill the tire with air under high pressure, the tire becomes rigid, able to exert forces in multiple directions. How can this be? It, like the wheel, is a pre-stressed structure, and the tire casing becomes rigid and able to exert forces in directions it can't when it is not pre-stressed. Likewise, the spokes in a pre-tensioned wheel can exert forces in direction that they normally can't when they are not in a pre-tensioned wheel.

And further consider - how does the tire transfer load to the rim, to keep the rim off the ground? The rim is not supported by pneumatic pressure - air pressure pushes with the same force in all directions, so the air pressure on the top is pushing the rim down with as much force as the air pressure on the bottom is pushing the rim up. Therefore, it must the tire casing fabric that is supporting the wheel. But how does a flexible fabric push upward on the rim?

There are more mechanical actions involved in tires (and wheels) than your simple viewpoint considers.

[Mark McM]

This discussion is getting a bit far afield of the original conversation, so I'll just add a few comments.


The bottom spokes have a change in stress/strain because of the unloading/loading cycles, not because they are ever compressed

This is where you are going astray. 'Compress' means to make shorter. The bottom spokes are clearly being compressed - direct measurements have shown that the bottom spokes get shorter when a wheel is loaded. This is a fact that you can't be denied, but that you haven't fully addressed. As long as the spokes never completely lose tension, they are just as rigid as they are lengthened or shortened from their static (pre-tensed) state.

If you built a wheel and put an enormous load on it without letting it roll, those 2 or 3 spokes on the bottom would simply dangle there as the rest of the spokes snapped under tension.

Not quite - as has been demonstrated many times (often by poorly landed jumps), a rim will usually buckle before the (top) spokes snap. In normal use the rim is kept from buckling by the support of the bottom spokes. As explained earlier, a wheel that has lost support of its bottom spokes is not a functioning wheel, and a non-functionling wheel is not instructive in how a functioning wheel works.

I think you've just fooled yourself into thinking that since the top spokes aren't doing all the work, something opposite than must be true. But what is really happening is that the work is evenly distributed to the evenly round shape of the rim, except where the rim's roundness has been mechanically interrupted by the small contact point of the ground.

By your arguments, I see that you both the lack the tools to analyze the mechanics of the wheel, nor have done any research on previous engineering analyses on wheel mechanics. I've already provided a few links, I can provide some more if you are actually interested.

As far as having "fooled myself", then you must think that is the case with all the other engineers who have studied the wheel, and come to the same conclusions that a wheel "stands" on its bottom spokes. And there are many engineers on that list.

[Kontact]

This is in correct, and we don't need to look very far from the wheel to find another example of flexible members becoming rigid in pre-stressed structures.

A bicycle tire is made of a flexible fabric casing - it has tensile strength, but no compressive strength. Air is a gas - it doesn't have a distinct shape or volume, let alone any (tensile strength). But when you fill the tire with air under high pressure, the tire becomes rigid, able to exert forces in multiple directions. How can this be? It, like the wheel, is a pre-stressed structure, and the tire casing becomes rigid and able to exert forces in directions it can't when it is not pre-stressed. Likewise, the spokes in a pre-tensioned wheel can exert forces in direction that they normally can't when they are not in a pre-tensioned wheel.

And further consider - how does the tire transfer load to the rim, to keep the rim off the ground? The rim is not supported by pneumatic pressure - air pressure pushes with the same force in all directions, so the air pressure on the top is pushing the rim down with as much force as the air pressure on the bottom is pushing the rim up. Therefore, it must the tire casing fabric that is supporting the wheel. But how does a flexible fabric push upward on the rim?

There are more mechanical actions involved in tires (and wheels) than your simple viewpoint considers.

I don't think saying that the hub is supported by all the spokes is "simple", but it is more complicated than comparing spokes to a fluid. The simple fact of the matter is the spokes are in fixed locations, the rim has a lot of compressive strength but is flexible, and that (unlike a tire), you can unload a specific part of the structure because the spokes in question are fixed in space.

Regardless, spokes work under tension, gas under compression. If you want to point to a compressive structure, consider a table top that sits loosely on four columns as legs. If the floor under one of those columns droops a little, the compression comes off that leg. Does this pull the table top in that corner the way you claim a spoke pushes? No, the compression just decreases in that leg and the other 3 legs do the work of holding the rigid table top up.

What I'm talking about is a localized phenomenon that happens solely because the rim isn't perfectly rigid and can distort with its contact with the ground. Hit the ground hard enough and it will actually become flat. Same forces. There are no spokes pressing out that can prevent that.

[Kontact]

You can test this by plucking a front wheel spoke (near the nipple) before and after you put weight on the handlebars. You'll find that
the only spokes to change are those about the tire contact patch on
the floor. These spokes are compressed and lose tension. If the load
is great enough, they will become slack and the wheel can collapse
sideways. In any case, a wheel can only bear loads that do not
consistently slacken the preload.

http://yarchive.net/bike/wheel_stresses.html

[Mark McM]

http://yarchive.net/bike/wheel_stresses.html

Exactly. Including this remark also in the linked posting:

That leaves it up to the observer to come to
terms with the description that "the wheel stands on the bottom
spokes".

[Kontact]

Exactly. Including this remark also in the linked posting:

And I'm saying that you haven't "come to terms with" it, since you said this:

At any time, only a few spokes are actually supporting the external load - these spokes are the spokes closest to the ground contact point.

All the spokes are supporting the external load, with the exception of the spokes that have lost their tension over the contact patch. That's what Brandt said in the quote, and it is the opposite of what I quoted you as saying.

Brandt is describing the wheel as a whole and the way you would measure the forces in them. Once you zero out preload, the forces in the wheel vary exactly the same way a wagon wheel would. But you have taken that observation and used it to come up with the odd conclusion that the only spokes supporting the hub are below it. That's your idea, and it is wrong.

[Mark McM]

All the spokes are supporting the external load, with the exception of the spokes that have lost their tension over the contact patch. That's what Brandt said in the quote, and it is the opposite of what I quoted you as saying.

Brandt is describing the wheel as a whole and the way you would measure the forces in them. Once you zero out preload, the forces in the wheel vary exactly the same way a wagon wheel would. But you have taken that observation and used it to come up with the odd conclusion that the only spokes supporting the hub are below it. That's your idea, and it is wrong.

Firstly, I don't think you are understanding what Brandt has said. Secondly, I think you reading too much into some of my statements.

I think you need to re-read the section of his book (linked previously) titled "Theory of the Spoked Wheel". You are saying that all the spokes bear the load EXCEPT the bottom few spokes. Brandt is saying that loads are borne PRIMARILY by the bottom few spokes. Here is a quote from the book, which I have bolded a few portions that support my point:

A wheel with wire spokes works the same as one with wooden spokes except that the built-in force in its spokes is different. In a wooden-spoked wheel, force is transmitted from the ground to the hub by compressing the bottom spoke. This spoke becomes shorter as it furnishes the upward force to the hub. As in a wooden-spoked wheel, the bottom spokes of a wire wheel become shorter under load, but instead of gaining in compression, they lose tension. With the same load, the net change in force is the same for both wheels. The algebraic sum of negative and positive forces (compression and tension) is the same.

That the bottom spokes support the wheel need not be taken on faith. An experiment will show that only a few spokes at the bottom of the wheel are affected by a vertical load. The relative tension of a spoke can be found by plucking it like a guitar string. The pitch of a spoke, just as the pitch of a guitar string, increases with more tension and decreases with less tension.


So, the bicycle wheel is like a wagon wheel, and a wagon wheel supports loads ONLY with the bottom spokes. The bicycle wheel is the same, the difference being that the bicycle wheel requires that the bottom spokes have a pre-tension greater than their compression load. And that pre-tension is achieved by the static pre-tension of ALL the spokes. In other words, the job of the bottom spokes is to bear the load, the job of the rest of the spokes is to keep the bottom spokes under net tension. All the spokes are required, but they do different things (which is exactly how every other pre-stressed structure works). I don't see anything I've said contradicting Brandt.

[Kontact]

Firstly, I don't think you are understanding what Brandt has said. Secondly, I think you reading too much into some of my statements.

I think you need to re-read the section of his book (linked previously) titled "Theory of the Spoked Wheel". You are saying that all the spokes bear the load EXCEPT the bottom few spokes. Brandt is saying that loads are borne PRIMARILY by the bottom few spokes. Here is a quote from the book, which I have bolded a few portions that support my point:




So, the bicycle wheel is like a wagon wheel, and a wagon wheel supports loads ONLY with the bottom spokes. The bicycle wheel is the same, the difference being that the bicycle wheel requires that the bottom spokes have a pre-tension greater than their compression load. And that pre-tension is achieved by the static pre-tension of ALL the spokes. In other words, the job of the bottom spokes is to bear the load, the job of the rest of the spokes is to keep the bottom spokes under net tension. All the spokes are required, but they do different things (which is exactly how every other pre-stressed structure works). I don't see anything I've said contradicting Brandt.
I think your misunderstanding is because you think a wagon wheel is fully supported by the bottom spokes. It isn't - without the compressive support of the rest of the spokes the rim, spoke and hub would not be able to maintain their relationship under any sort of side load. Picture a table with skinny legs and no bracing - nudge the table and the legs just fold.

Because you think a wagon wheel is just balanced on whatever spoke is on the bottom, you think that's an accurate model of what a wheel is. But a wagon wheel is a balance compression structure, while a bicycle wheel is a balanced tension structure. In both cases the structural integrity of the rim comes from it being pushed out or pulled in by spokes.

In other words, you couldn't have wagon wheel where the extendable spokes only went to full length at the bottom of the rotation. The rim would collapse.

The bottom spokes are "taking a load" but that isn't the same as supporting the hub. They are under net tension, and "the load" is a decrease in tension to those spokes.

Brandt was making about point about net forces, not telling you that you can push a string uphill.

[Mark McM]

I think your misunderstanding is because you think a wagon wheel is fully supported by the bottom spokes. It isn't - without the compressive support of the rest of the spokes the rim, spoke and hub would not be able to maintain their relationship under any sort of side load. Picture a table with skinny legs and no bracing - nudge the table and the legs just fold.

Because you think a wagon wheel is just balanced on whatever spoke is on the bottom, you think that's an accurate model of what a wheel is. But a wagon wheel is a balance compression structure, while a bicycle wheel is a balanced tension structure. In both cases the structural integrity of the rim comes from it being pushed out or pulled in by spokes.

In other words, you couldn't have wagon wheel where the extendable spokes only went to full length at the bottom of the rotation. The rim would collapse.

The bottom spokes are "taking a load" but that isn't the same as supporting the hub. They are under net tension, and "the load" is a decrease in tension to those spokes.

Brandt was making about point about net forces, not telling you that you can push a string uphill.

It's not clear to me what point you are trying to make here. This appears to be a strawman, to divert attention from your failing arguments about how wheels support vertical loads. Are you going to claim that bicycle wheels "hang from their top spokes" when under lateral loading, too?

[Kontact]

It's not clear to me what point you are trying to make here. This appears to be a strawman, to divert attention from your failing arguments about how wheels support vertical loads. Are you going to claim that bicycle wheels "hang from their top spokes" when under lateral loading, too?

If you are going to claim a strawman, point to it. I don't know what you are talking about.

I have disagreed with your assertion that the bottom spokes "support the load". The load of the rider's weight is supported by how the rims and hub are connected by tensioned spokes. The rim is kept from collapsing as much from vertical spokes but horizontal ones that force it to remain round. Under load, the hub is net "hanging" from the upper 180° of tensioned spokes just as it would be supported by the lower 180° of compressive spokes in a wagon wheel. Brandt's point is that this doesn't matter because the distributed pre-tension or pre-compression is so much higher than the actual load that nothing measurably changes - the rim remains round and the spokes don't get longer or shorter.

The exception is the spokes over the contact patch that are actually changing length. On compressive spokes they are compressed shorter, and on tensioned spokes they are allowed to relax shorter. And that happens not because of the direction of force (up and down), but because of the mechanical fact that a circular rim touches the flat earth at a tangent, creating a point stress on the rim. That point stress takes the rim out of round and affects the spokes directly above it.

Mount bike the on rollers and all of a sudden your spokes that "take the load" aren't the ones directly under the hub, but the two sets between the hub and each roller. And it is only happening because those are the two points distorting the roundness of the rim. Put a wheel in a cradle with the same curve as the rim and you wouldn't detect any load at all.

"The load" Brandt is talking about is just the mechanical measured change in spoke compression, not a useful description of how hub fails to fall into the rim (how the rider is supported). The rider is supported by distributed tension throughout the wheel, and not by a single section of spokes pushing up. Especially not spokes in capable of gross compression.

[Mark McM]

If you are going to claim a strawman, point to it. I don't know what you are talking about.

I have disagreed with your assertion that the bottom spokes "support the load". The load is supported by how the rims and hub are connected by tensioned spokes. The rim is kept from collapsing as much from vertical spokes but horizontal ones that force it to remain round. Under load, the hub is "hanging" from upper 180° of tensioned spokes just as it would be supported by the lower 180° of compressive spokes in a wagon wheel. Brandts point is that this doesn't matter because the distributed pre-tension or pre-compression is so much higher than the actual load that nothing changes - the rim remains round and the spokes don't get longer or shorter.

The exception is the spokes over the contact patch that are actually changing length. On compressive spokes they are compressed shorter, and on tensioned spokes they are allowed to relax shorter. And that happens not because of the direction of force (up and down), but because of the mechanical fact that a circular rim touches the flat earth at a tangent, creating a point stress on the rim. That point stress takes the rim out of round and affects the spokes directly above it.

Mount bike on rollers and all of a sudden your spokes that "take the load" aren't the ones directly under the hub, but the two sets over each roller. And it is only happening because those are the two points distorting the roundness of the rim. Put a wheel in a cradle with the same curve as the rim and you wouldn't detect any load at all.

"The load" is just the mechanical measured change in spoke compression, not a useful description of how hub fails to fall into the rim.

So, that wagon wheel question was just a strawman then?

I think my argument can be summed up by these lines from the Keith Bontrager interview:

If you looked at the change in tension when a load is applied to a wheel, the tension in all the spokes away from the contact-patch area doesn’t change. The weight is not hanging from the spokes. The tension is _reduced_ across the contact patch; the wheel is standing on those spokes. The change in tension is the same as the compressive load.

Whether you want to say that the bottom spokes support the load, or that the bottom spokes merely pull down on the hub less (while the rest of the spokes actually support the load), may sound like just a symantic argument, but I say it is not, and here's why: Focusing on the bottom spokes is a better way to design and build good wheels.

Firstly, this view is better at keeping one mindful that one of the most important factor in making a strong a durable wheel is making sure that the bottom spokes remain in net tension.

Secondly, it reminds one that the wheel will only durable if there are sufficient number of spokes in the LAZ, which means matching the number (and type) of spokes to the rim radial stiffness.

Thirdly, disregarding crashes and other extreme events, spokes fail under fatigue, which is result of a high number of loading cycles - and these loading cycles occur as spokes enter and leave the LAZ at the bottom of the wheel as the wheel rotates.

The viewpoint that wheels are supported by a few spokes at the bottom ("the wheel stands on the bottom spokes") is far more useful in regard to engineering and building wheels than the "wheels hang from all the spokes" viewpoint. The bottom of the wheel is where all the important action is, and concentrating elsewhere is just a distraction.

[Kontact]

So, that wagon wheel question was just a strawman then?

I think my argument can be summed up by these lines from the Keith Bontrager interview:



Whether you want to say that the bottom spokes support the load, or that the bottom spokes merely pull down on the hub less (while the rest of the spokes actually support the load), may sound like just a symantic argument, but I say it is not, and here's why: Focusing on the bottom spokes is a better way to design and build good wheels.

Firstly, this view is better at keeping one mindful that one of the most important factor in making a strong a durable wheel is making sure that the bottom spokes remain in net tension.

Secondly, it reminds one that the wheel will only durable if there are sufficient number of spokes in the LAZ, which means matching the number (and type) of spokes to the rim radial stiffness.

Thirdly, disregarding crashes and other extreme events, spokes fail under fatigue, which is result of a high number of loading cycles - and these loading cycles occur as spokes enter and leave the LAZ at the bottom of the wheel as the wheel rotates.

The viewpoint that wheels are supported by a few spokes at the bottom ("the wheel stands on the bottom spokes") is far more useful in regard to engineering and building wheels than the "wheels hang from all the spokes" viewpoint. The bottom of the wheel is where all the important action is, and concentrating elsewhere is just a distraction.

I still don't know what argument you consider "straw man".

As far as all this goes,
"Whether you want to say that the bottom spokes support the load, or that the bottom spokes merely pull down on the hub less (while the rest of the spokes actually support the load), may sound like just a symantic argument, but I say it is not, and here's why: Focusing on the bottom spokes is a better way to design and build good wheels. "
it isn't semantic. You appear to be arguing that a flawed physics model is better if it makes engineering easier. And maybe it does make it easier to design a wheel, but that doesn't mean it should be a substitute for reality.


Wheels support weight like a suspension bridge rolled up in a circle. If wind lifts a section of the bridge frequently, that will unload those cables. We wouldn't argue that those cables are supporting the lifted roadway, so it doesn't make sense to say the LAZ spokes are supporting the hub.

What the LAZ spokes are doing is going through stress cycles, because the tension keeps coming on and off. If you rolled a wagon and bike wheel until spoke failure, the wagon spokes would fail as they came into the LAZ and compressed, and the bike wheel spokes would fail as the spokes came out of LAZ as they re-tensioned. That might not be important to an engineer trying to do a job, but it is completely different physically.

Additionally, if you took both kinds of wheels and loaded them statically until failure, the wagon spoke on the bottom would compress until it shattered, while the bike spokes along the top will break first. And if you eliminate the LAZ compression by using a rim that can't change shape, the same thing will happen as the net tension just increases on the top spokes.


So while I fully appreciate that bike wheels are designed around the transient tensions at the LAZ and the damage those work cycles cause, it doesn't make a suspension wheel into a compression wheel in reality. It is okay to acknowledge reality even if reality isn't particularly useful to a wheel builder or rim designer.

[bikinchris]

Years ago, I had started talking to people standing around at the mechanic stand at a multi day ride. The conversation turned to wheels and I mentioned that wheels actually stand on the spokes and it blew everyone's mind. After getting a little flack, I just walked away.

[Kontact]

It sounds like counter-steering being how a bike is steered. People talk about it like it with surprise, but it isn't really accurate either.

[wallymann]

fwiw...this FEA suggests that moderate loads (when the bottom/vertical spokes retain some tension) are carried by increased tension in the spokes just fore-aft of bottom/vertical spokes.

https://scontent-atl3-1.xx.fbcdn.net/v/t1.0-9/23473281_10213307392031200_5407620071812563968_n.j pg?oh=d0df4927846dcb1a8b89a111876ad292&oe=5AA4B70B

watch the video to see how the loads change around the wheel as the overall weight borne is increased.

https://www.youtube.com/watch?v=w4kz0k4AdI4

[oldpotatoe]

winter already??

Yikes..:eek:

[ultraman6970]

Yeah, nothing else to do :P

Probably a manufacturer will hire some temps to focus in a new study how a 55 mm wide clincher tire at 10 psi is faster, cadillac softer than anything invented before.

[Hindmost]

This is one of the best images I can find. I am seeing 28 front and 32 rear; 3x. Man, the rims look narrow.

[wallymann]

the entire wheel system takes the load when bearing weight and functioning as as wheel. individual parts may deform locally and may see stresses change, but any attempts to decompose the system to identify which sub-parts "bear the load" are folly.

a hub hanging from a rim by a handful of spokes may bear a load, but it's not a wheel -- its a hub hanging from spokes.

a hub standing on a handful of solid spokes extending from a rim may bear a load, but it's not a wheel -- it's a hub standing on spokes.

the wheel system bears the load. without the system, it's not a wheel.

[makoti]

My first real race bike was built in ‘86. The sponsor built me a set of race wheels that was record hubs and gp4 rims. Tubies glued with Fastac.

I had a set exactly like this.

[makoti]

This is one of the best images I can find. I am seeing 28 front and 32 rear; 3x. Man, the rims look narrow.

They were running 21's on them.

[Mark McM]

I still don't know what argument you consider "straw man".

The wagon wheel analogy only pertains to vertical loads. Like all analogies, the comparison between the two has its limits, and the similarities may break down when you get out of the scope of the analogy. When it comes to lateral loading, wagons and bicycles are quite different, so trying to stretch the analogy in this direction is not instructive.


As far as all this goes,
"Whether you want to say that the bottom spokes support the load, or that the bottom spokes merely pull down on the hub less (while the rest of the spokes actually support the load), may sound like just a symantic argument, but I say it is not, and here's why: Focusing on the bottom spokes is a better way to design and build good wheels. "
it isn't semantic. You appear to be arguing that a flawed physics model is better if it makes engineering easier. And maybe it does make it easier to design a wheel, but that doesn't mean it should be a substitute for reality.

No models are perfect, because they are simplified reflections of reality that are only useful within certain constraints. Both the "wheel stands on the bottom spokes" nor the "wheel is supported by the spokes above the hub" are simplifications, and neither is a perfect representations of reality. But because it is either impossible or unwieldy to try to develop and use a model which incorporates ALL physical laws, we need to choose the model that produces the most useful results. As long as we stay within its contraints, the model of the wheel that gives the best results is the one in which the wheel stands on its spokes.


Wheels support weight like a suspension bridge rolled up in a circle. If wind lifts a section of the bridge frequently, that will unload those cables. We wouldn't argue that those cables are supporting the lifted roadway, so it doesn't make sense to say the LAZ spokes are supporting the hub.

Once again you are building a model, and then pushing it past the constraints where the model is valid. Just as the suspension cables only support the decking as long as they remain under tension, the botton spokes of the wheel only support the load if they remain under tension. In both cases, if the cables or spokes are allowed to completely slacken, the model is invalid, and/or the design based on that model has failed.

From many of your comments, there is one important point that you don't seem to have come to grips with (or don't want to address), and that is that pre-tensioned spokes have high stiffness in compression. As we have agreed, when under load, the rim at the bottom of the wheel flattens out and the spokes shorten, i.e., the wheel deflects inward toward the hub. But how much does the wheel deflect, and which elements determine it? The wheel deflection is governed primarily by the (compressive) stiffness of the spokes at the bottom of the wheel.

We can shows this from a simple thought experiment. What if we replaced some of the spokes with rubber bands? Lets say that these rubber bands were just as strong steel spokes, but much more elastic (less longitudinal stiffness). If the tension in the rubber bands were the same as the spokes they replaced, the wheel would be just as round and balanced as before.

If we replace just the bottom spokes with rubber bands and applied a vertical load, the rim would have little support to prevent it from bending inward, and the would deflect more than before. But if the bottom spokes were steel and we replace the rest of the spokes with rubber bands, the rim would deflect about the same amount as it did when all the spokes were steel. It is the spokes directly between the hub and ground that most affect the vertical deflection (compression) of the wheel under load.

So, we have to ask ourselves - if the deflection (compression) of the wheel under load is governed largely by the stiffness of the bottom spokes, how can we claim that the wheel loads are not supported by the bottom spokes?

[Mark McM]

fwiw...this FEA suggests that moderate loads (when the bottom/vertical spokes retain some tension) are carried by increased tension in the spokes just fore-aft of bottom/vertical spokes.

Well ... not quite. As can be seen, the bottom of the rim flattens out under load. This flattening is what causes the rim to bulge out just fore/aft of the flattened area, and the tension of the spokes in the bulges does increase. But since the bulges are below the hub, the corresponding tension increases actually pull down more on the hub, and not act to hold the hub up.

You'll also notice that as the rim flattens at the bottom, at causes the diameter of the rim around the rest of the wheel to slightly increase. This causes small increases in the spoke tensions around the rest of the wheel.

So, we can see that there are tension changes all the way around the wheel. But looking at the magnitudes of the changes shows some interesting things:

The total upward force at the hub due to tension increases in the spokes above the hub are much smaller than the vertical load on the wheel. Therefore can not say that the wheel bears its load by tension increase in the top of the wheel

The tension changes at the top of the wheel are about the same as the tension changes at the front and back of the wheel (and we also know that the horizontal components of spoke tension changes can't act to hold the hub up). So it is reasonable to conclude that these small uniform tension changes around most of the rim are primarily due to the diameter increases around the rim as if flattens at the bottom.

The total vertical force change at the hub due to tension changes of just a few spokes at the bottom of the wheel has nearly the same magnitude as the load on the wheel. Therefore it is reasonable to conclude that the spoke tension changes that support the wheel load are the tension changes at the bottom of the wheel.

[Mark McM]

the entire wheel system takes the load when bearing weight and functioning as as wheel. individual parts may deform locally and may see stresses change, but any attempts to decompose the system to identify which sub-parts "bear the load" are folly.

a hub hanging from a rim by a handful of spokes may bear a load, but it's not a wheel -- its a hub hanging from spokes.

a hub standing on a handful of solid spokes extending from a rim may bear a load, but it's not a wheel -- it's a hub standing on spokes.

the wheel system bears the load. without the system, it's not a wheel.

I can't disagree with this. Every component (the rim, hub and every spoke) plays a role in supporting the wheel loads. The bottom spokes have a somewhat dynamic role, while the rest of the spokes have a more static, but no less important, role. My point in this discussion has been that all too often, the role of the bottom spokes is greatly under appreciated.

[Kontact]

The wagon wheel analogy only pertains to vertical loads. Like all analogies, the comparison between the two has its limits, and the similarities may break down when you get out of the scope of the analogy. When it comes to lateral loading, wagons and bicycles are quite different, so trying to stretch the analogy in this direction is not instructive.
You seem to be complaining about an extended analogy, but calling it a straw man. You should look up what a straw man is, because it is kind of an insulting term and it isn't what you mean.


From many of your comments, there is one important point that you don't seem to have come to grips with (or don't want to address), and that is that pre-tensioned spokes have high stiffness in compression. As we have agreed, when under load, the rim at the bottom of the wheel flattens out and the spokes shorten, i.e., the wheel deflects inward toward the hub. But how much does the wheel deflect, and which elements determine it? The wheel deflection is governed primarily by the (compressive) stiffness of the spokes at the bottom of the wheel.

We can shows this from a simple thought experiment. What if we replaced some of the spokes with rubber bands? Lets say that these rubber bands were just as strong steel spokes, but much more elastic (less longitudinal stiffness). If the tension in the rubber bands were the same as the spokes they replaced, the wheel would be just as round and balanced as before.

If we replace just the bottom spokes with rubber bands and applied a vertical load, the rim would have little support to prevent it from bending inward, and the would deflect more than before. But if the bottom spokes were steel and we replace the rest of the spokes with rubber bands, the rim would deflect about the same amount as it did when all the spokes were steel. It is the spokes directly between the hub and ground that most affect the vertical deflection (compression) of the wheel under load.

So, we have to ask ourselves - if the deflection (compression) of the wheel under load is governed largely by the stiffness of the bottom spokes, how can we claim that the wheel loads are not supported by the bottom spokes?

Pre-tensioned spokes don't have "high stiffness under compression" because they aren't compressed. That isn't happening, that isn't an engineering or physics concept and you are referring to it without any reference to actual science.

There are structures that use a mixture of pre-tensioned elements with compressed elements to become stronger, but spokes are only tensioned. They do all their work through their tensile strength and don't need to have any compressive stength, which is why even kevlar strands can serve as spokes, as in the Tiogo Tension Disc.


You keep referring to forces that aren't found in spokes, and I don't understand why. Decreasing tension is NOT compression. Until you hit zero tension there is no compression going on in the spoke, and no claim of compressive strength applies. The wheel as a complete structure is a combination of compressive rim strength and tensile spoke strength, but the LAZ section is simply a transient violation of the wheel's structure, not the key to how spokes work.

You can't stand something on the top of a string, and there is no point in discussing anything as if you could.

[Kontact]

fwiw...this FEA suggests that moderate loads (when the bottom/vertical spokes retain some tension) are carried by increased tension in the spokes just fore-aft of bottom/vertical spokes.


watch the video to see how the loads change around the wheel as the overall weight borne is increased.

https://www.youtube.com/watch?v=w4kz0k4AdI4

That's a great video, thanks for posting it.

If you go to settings on the lower right you can slow down the video and watch the tension change.

The high tension at 5 and 7 o'clock are caused by the way the rim is trying to remain round despite the dent at 6 o'clock. With an unbendable rim or weak spokes you wouldn't get a pattern like that because other spokes would fail before the rim distorted. The pattern also comes from the lacing - radial lacing would behave a little more simply.

[carpediemracing]

The wheel is a classic pre-stressed structure. At any time, only a few spokes are actually supporting the external load - these spokes are the spokes closest to the ground contact point. The rest of the spokes are there to maintain the pre-tension on the load supporting spokes. The role of rim stiffness is that a stiffer rim distributes loads over a wider area, thus allowing the spokes to be further apart and still have the same number of spokes bearing the load. And spokes being further apart means fewer total spokes. So modern wheels can have fewer spokes not because the rim is stronger, but because the rim is stiffer.

Technically I misspoke, but the modern rims are significantly stiffer and stronger. I guess my interpretation of my observations were faulty.

Still, though, the hallmark of an "old school racing wheel" for me is that of a very light rim with a lot of spokes, relatively speaking.

I never experienced wood rims and all that so maybe someone would say that that's really the old school racing wheel, if one wants to get technical.

[carpediemracing]

This is one of the best images I can find. I am seeing 28 front and 32 rear; 3x. Man, the rims look narrow.

Based on the clearance of the brakes (I had a set personally) those are really narrow wheels, probably 17-18mm rims with 18mm tires.

The Sun Metal M17 tubulars were 17mm wide and cheap (and cheaply made). I ran it for a while, using a 17mm Panaracer tire. Wolber made a better 18mm tire (it was cotton, not nylon) but I couldn't afford it. Ironically a few years ago someone gave me a Wolber 18mm tire for my M17 wheel, which I still have. Never used it, was going to use it on the track.

I think Assos made a similar narrow aero rim, it was one of the first low spoke count wheels I saw, 24H or so.

If you look at Chiapucci in the final TT of the 1990 Tour, you'll see he's on similar wheels, probably 18mm tires, ultra skinny. Lemond, on the other hand was on something a bit wider, maybe 21mm? but with aero wheels and aero bars.

I can't find still pictures but the video shows the tiny tires:
https://www.youtube.com/watch?v=MhOdsv74XK4

*edit might be 20mm tires? These are 21mm tires on FiR Isidis, 28/32, 3x, with my favorite 1.8DB front, 1.8DB/2.0DB rear, alloy spoke nipples, with 21mm CX tires. My bike, from 1991 or 1992. Due to lack of availability I stayed with 32H rear wheels.

http://4.bp.blogspot.com/_TbmplkIYLx8/S-scIxcTr0I/AAAAAAAACzk/xXhVzK3t-jo/s800/IMG_0050.jpg

[Kontact]

Technically I misspoke, but the modern rims are significantly stiffer and stronger. I guess my interpretation of my observations were faulty.

Still, though, the hallmark of an "old school racing wheel" for me is that of a very light rim with a lot of spokes, relatively speaking.

I never experienced wood rims and all that so maybe someone would say that that's really the old school racing wheel, if one wants to get technical.

If we are using the engineering term "strength", then stiffness is pretty much identical to strength.

[Black Dog]

MarK MCM and Kontact thanks for this discussion. It has been most fascinating and enlightening, indeed. It looks like you are both a lot closer to agreement than it may feel. It looks like semantics and not syntax are keeping you apart from a beer and a hug. None the less, if you two are not ready to buy each other a beer I would certainly buy you both one as thanks for sharing some serious technical knowledge. :beer:

[ripvanrando]

I raced on 32H x3 GL330 or GP4 36H 3x on good roads. I was 170 lbs

I now ride 20H radial 28h 2X clinchers on lousy roads. I am now north of 200lb but not much

Back in the day, I'd get flats and break a couple spokes a year.

Now, not many flats and no broken spokes in around 40,000 miles.

[Mark McM]

You seem to be complaining about an extended analogy, but calling it a straw man. You should look up what a straw man is, because it is kind of an insulting term and it isn't what you mean.

Strawman (https://en.wikipedia.org/wiki/Straw_man): "straw man is a common form of argument and is an informal fallacy based on giving the impression of refuting an opponent's argument, while refuting an argument that was not presented by that opponent."

We weren't discussing how wagons deal with lateral loads. Thus your introduction of this topic was a straw man.


Pre-tensioned spokes don't have "high stiffness under compression" because they aren't compressed. That isn't happening, that isn't an engineering or physics concept and you are referring to it without any reference to actual science.

There are structures that use a mixture of pre-tensioned elements with compressed elements to become stronger, but spokes are only tensioned. They do all their work through their tensile strength and don't need to have any compressive stength, which is why even kevlar strands can serve as spokes, as in the Tiogo Tension Disc.

Pre-stressing of structures isn't just done to improve strength, it can also be done to improve stiffness. For example, by allowing what are normally tension-only members to contribute to stiffness when they are compressed (de-tensioned).

You seem to be hung up on artifically narrow definitions of words. "Compressive" and "compress" just mean making smaller/shorter. They don't have to refer to an absolute value. In this way, a spoke with an (absolute) pre-tension force can be subjected to a (relative) compression force. Since the wheel load shortens the spoke, it by definition applies a compressive load on the spoke (even if the spoke remains in net tension). One of the purposes of pre-stressed structures is that it allows us to change our reference planes

You also seem to keep dodging the fact that spokes can exhibit high stiffness in (relative) compression. I had hoped that the thought experiment I offered would illustrate this, but it appears not. So, here's an even simpler thought experiment, with a simple pre-stressed structure:

You have a 1 foot long hollow metal tube. The tube is fat enough that it can bear longitudinal loads in both tension and compression. The tube has a longitudinal stiffness of 10,000 lb/in. If you put the tube under 100 lb. of tension, the tube stretches 0.01" and if you put the tube under 100 lb. of compression the tube shortens by 0.01".

You also have a 1 foot straight pull spoke. Say that this spoke has a stiffness in tension of 10,000 lb/in, just like the tube. If you put the spoke under 100 lb. of tension, it stretches 0.01". But when it is in its free state, this spoke will buckle under compressive load. The spoke it its free state has a compressive stiffness of effectively zero.

Now we construct a pre-stressed structure with the tube and spoke. The spoke is placed inside and co-axial to the center of the tube, and anchored to plates covering the ends of the tube. The head of the spoke is anchored in a hole in the plate at one end of the tube, and threaded end of the spoke is screwed into a nipple anchored in a hole in the plate at the other end of the tube. The nipple is tightened until the spoke is loaded to a pre-tension of 200 lb. This is now a pre-stressed structure.

Put the combined tube/spoke structure under 100 lb. of tension - now how much does it stretch? The tube and the spoke are loaded in parallel, so the stiffnesses of the tube and the spoke combine. The total stiffness is 20,000 lb/in, so the structure now stretches only 0.005". Pretty straight forward.
But what if you put the combined tube/spoke structure under 100 lb. of compression? Since only the tube has a compressive stiffness when the structure is not assembled, does the combined structure only have a stiffness of 10,000 lb? No. The tube and the spoke structure still have a combined stiffness of 20,000 lb/in - just like it does in tension. The structure will compress only 0.005".

The question is: If the tube by itself only has a compressive stiffness of 10,000 lb/in, but the compressive stiffness of the pre-stressed structure is 20,000 lb/in, where did the extra compressive stiffness come from? The only answer can be the spoke provides that stiffness. And it does this even the load is acting to shorten (compress) the spoke.

So, there you go - a simple example showing a spoke that clearly exhibits a compressive stiffness. If you do not see this, than you many not have the analytic tools to understand a bicycle wheel. Some of the arguments here may be about symantics and reference planes, but this one is not.


You can't stand something on the top of a string, and there is no point in discussing anything as if you could.

There's a little trick that bike mechanics sometimes use to thread cable housings through internally routed frames. They first push a string through the frame, and then run the housing over the string. But how do you push a string through the frame? One way is to apply a vaccuum to the exit hole, and then feed the string in through the entry hole, until the string comes out through the exit hole. "But," you say, "you aren't pushing the string through the frame, you are pulling it with the vaccuum!" Wrong. A vaccuum doesn't provide a force - a vaccuum can't pull anything. The string isn't being pulled, it is being pushed.

But ... is it actually wrong to think of it as the string being pulled through the frame?

[Kontact]

Strawman (https://en.wikipedia.org/wiki/Straw_man): "straw man is a common form of argument and is an informal fallacy based on giving the impression of refuting an opponent's argument, while refuting an argument that was not presented by that opponent."

We weren't discussing how wagons deal with lateral loads. Thus your introduction of this topic was a straw man.
Then I'm not sure why you posted this:

So, the bicycle wheel is like a wagon wheel, and a wagon wheel supports loads ONLY with the bottom spokes. The bicycle wheel is the same, the difference being that the bicycle wheel requires that the bottom spokes have a pre-tension greater than their compression load.


Pre-stressing of structures isn't just done to improve strength, it can also be done to improve stiffness. For example, by allowing what are normally tension-only members to contribute to stiffness when they are compressed (de-tensioned).
Stiffness and strength, in basic engineering speak, are the same thing. A "strong" structure is one that resists deforming along whatever axis you're interested in.


You seem to be hung up on artifically narrow definitions of words. "Compressive" and "compress" just mean making smaller/shorter. They don't have to refer to an absolute value. In this way, a spoke with an (absolute) pre-tension force can be subjected to a (relative) compression force. Since the wheel load shortens the spoke, it by definition applies a compressive load on the spoke (even if the spoke remains in net tension). One of the purposes of pre-stressed structures is that it allows us to change our reference planes

It isn't relative. Materials have tensile strengths and compression strength and sheer strength. The terms are not interchangeable, or we wouldn't have materials that are strong in compression but weak in tension. Spokes have zero compression strength. This isn't a matter of how you look at things, it is a solidly understood engineering concept.


You also seem to keep dodging the fact that spokes can exhibit high stiffness in (relative) compression. I had hoped that the thought experiment I offered would illustrate this, but it appears not. So, here's an even simpler thought experiment, with a simple pre-stressed structure:

You have a 1 foot long hollow metal tube. The tube is fat enough that it can bear longitudinal loads in both tension and compression. The tube has a longitudinal stiffness of 10,000 lb/in. If you put the tube under 100 lb. of tension, the tube stretches 0.01" and if you put the tube under 100 lb. of compression the tube shortens by 0.01".

You also have a 1 foot straight pull spoke. Say that this spoke has a stiffness in tension of 10,000 lb/in, just like the tube. If you put the spoke under 100 lb. of tension, it stretches 0.01". But when it is in its free state, this spoke will buckle under compressive load. The spoke it its free state has a compressive stiffness of effectively zero.

Now we construct a pre-stressed structure with the tube and spoke. The spoke is placed inside and co-axial to the center of the tube, and anchored to plates covering the ends of the tube. The head of the spoke is anchored in a hole in the plate at one end of the tube, and threaded end of the spoke is screwed into a nipple anchored in a hole in the plate at the other end of the tube. The nipple is tightened until the spoke is loaded to a pre-tension of 200 lb. This is now a pre-stressed structure.

Put the combined tube/spoke structure under 100 lb. of tension - now how much does it stretch? The tube and the spoke are loaded in parallel, so the stiffnesses of the tube and the spoke combine. The total stiffness is 20,000 lb/in, so the structure now stretches only 0.005". Pretty straight forward.
But what if you put the combined tube/spoke structure under 100 lb. of compression? Since only the tube has a compressive stiffness when the structure is not assembled, does the combined structure only have a stiffness of 10,000 lb? No. The tube and the spoke structure still have a combined stiffness of 20,000 lb/in - just like it does in tension. The structure will compress only 0.005".

The question is: If the tube by itself only has a compressive stiffness of 10,000 lb/in, but the compressive stiffness of the pre-stressed structure is 20,000 lb/in, where did the extra compressive stiffness come from? The only answer can be the spoke provides that stiffness. And it does this even the load is acting to shorten (compress) the spoke.

So, there you go - a simple example showing a spoke that clearly exhibits a compressive stiffness. If you do not see this, than you many not have the analytic tools to understand a bicycle wheel. Some of the arguments here may be about symantics and reference planes, but this one is not.

What you've just explained above is why a rim that has compressive strength is made stronger by spokes with only tensile strength. And it is 100% true.

But when we flex the rim at the LAZ, the spokes directly above the LAZ are no longer adding their full tension to that structure, and if you are talking about those spokes, rather than all the spokes together, you are not talking about "compression". The compression is what the spokes pull the rim into, not what the spokes do to push on the hub. If you change the shape of the rim, the spokes in that spot aren't contributing to the wheel strength as much.

You've taken the concept of the wheel and tried to apply it to a single component of the wheel.



There's a little trick that bike mechanics sometimes use to thread cable housings through internally routed frames. They first push a string through the frame, and then run the housing over the string. But how do you push a string through the frame? One way is to apply a vaccuum to the exit hole, and then feed the string in through the entry hole, until the string comes out through the exit hole. "But," you say, "you aren't pushing the string through the frame, you are pulling it with the vaccuum!" Wrong. A vaccuum doesn't provide a force - a vaccuum can't pull anything. The string isn't being pulled, it is being pushed.

But ... is it actually wrong to think of it as the string being pulled through the frame?

In that case, you are carrying a string along in the flow of air, you aren't pushing or pulling it. It will travel through the tube without having any measurable strength at all. That isn't a useful example because the airflow isn't just acting on the ends of the strings but along its entire length.


I would be happy to buy you a beer, and hope no one is bothered by this debate. But a wheel works differently than the parts it is made of, and tension is not compression in reverse. Your examples are even better than mine for why a hub isn't sitting on the spokes below it.

[Hindmost]

Based on the clearance of the brakes (I had a set personally) those are really narrow wheels, probably 17-18mm rims with 18mm tires...

Mavic had the CX18 available at that time, supposedly for track use. I can't help but wonder that they didn't use some of their lighter rims, they are all dark anodized, and relabel them SSC.

[Mark McM]

Well, obviously at this point we're going to have to just agree to disagree. This will be my last post here, so I'll just add a few more comments before signing off.

Stiffness and strength, in basic engineering speak, are the same thing. A "strong" structure is one that resists deforming along whatever axis you're interested in.

Stiffness and strength are not at all the same thing. And we can not analyze statically indeterminent structures (https://en.wikipedia.org/wiki/Statically_indeterminate) (like bicycle wheels) without knowing how the stiffnesses of the elements interact. If you knew anything about structural analysis, you'd know this, so I can only assume that you haven't done much structural analsys.

It isn't relative. Materials have tensile strengths and compression strength and sheer strength. The terms are not interchangeable, or we wouldn't have materials that are strong in compression but weak in tension. Spokes have zero compression strength. This isn't a matter of how you look at things, it is a solidly understood engineering concept.

I'm not disgreeing. But a well designed pre-stressed structure acts to keep all members within their loading modes where they are strongest, and keep them out of loading modes where they are weakest. For example, in a bicycle wheel, verticals loads will act so as to compress the bottom spokes. But these spokes are under a high pre-tension, so that when the compression from the vertical load is super-imposed on the bottom spokes, they remain in net tension.


What you've just explained above is why a rim that has compressive strength is made stronger by spokes with only tensile strength. And it is 100% true.

Yes, but I've explained more than that. As you say, when the wheel is loaded, the rim bends inwards. But how much does it bends inward? Which properties of which elements matter the most to determine this? If we don't know these answers, we can't know how the forces are re-balanced when the wheel is loaded, and therefore can't ensure that we are designing wheels with adequate strength and durability. What I've been trying (and apparently failing) to explain is why the stiffnesses of the (bottom) spokes matters so much in determining the re-balancing of the forces. (This goes back to statically indeterminant structure analysis mentioned above). Without knowing this, we can get a hint of how wheels react under load, but we can't get the whole story and will miss a big part of the picture.


In that case, you are carrying a string along in the flow of air, you aren't pushing or pulling it. It will travel through the tube without having any measurable strength at all. That isn't a useful example because the airflow isn't just acting on the ends of the strings but along its entire length.


I would be happy to buy you a beer, and hope no one is bothered by this debate. But a wheel works differently than the parts it is made of, and tension is not compression in reverse. Your examples are even better than mine for why a hub isn't sitting on the spokes below it.

Well, technically we are pushing the string (air can't really pull) - but as you say, we are pushing along the entire length (not just the ends). The point I was trying to make is that we often model "vaccuum" as providing a pulling force - just like we make models use centrifugal force, coriolis force and even gravity force, which science has shown are actually fictitious forces (https://en.wikipedia.org/wiki/Fictitious_force). But even if these forces don't really exist, it is very useful and generally not harmful to consider to model them as real. Likewise, while the bottom spokes of a properly functioning wheel are always in net tension, it is very useful and not harmful to analyze the forces superimposed on them from wheel loads as a compressive forces.

And yes, I'd be happy to have a beer with you.

[72gmc]

In ‘86 I was on shimano 600 hubs laced 32/3-cross to Matrix rims (new Trek 560). That year or early ‘87 I upgraded to tricolor Ultegra hubs, MA40 rims, and awesomely narrow avocet tires.

And I’ll have a beer, too.

[AngryScientist]

well this thread has taken an interesting side road.

mark and kontact - very good discussion! i think you are both discussing purely academic concepts with regard to wheel mechanics. i'm a dorky engineer also and can appreciate picking the details apart, and have learned a few things by reading through the discussion and links provided.

to the point - it will never happen - but it would be neat to see some pro level competitors go head to head on a real road race course with 1980's equipment pitted against 2017 tech and see just how much of an advantage the latest stuff has in a real race scenario.

good stuff here in this thread, and i applaud the participants for an open, fun discussion with lots of stuff on the table.