Sapim Strong: Broke yet another spoke

[redir]

I had no idea there was this much to it. So I guess there is something to be said for used hubs then huh? As long as you lace the wheel so that you use the same indentations right?

And... Guess what? On my commute this morning to work just cruising along on some flat smooth ground and..... PING!!!!!!! Huh? What the....


Broke a spoke... AGAIN!!!!


I hit no bumps, was not putting any power in the wheel, just cruising along. Ultergra hub with Open Pro 32 spoke wheel. Wheels that I purchased about ten years ago for the specific reason of being pit wheel in criteriums and as back up for road races. So while they are ten years old they really do not have a lot of miles. About 5 years ago I started commuting on them but that's only 20 miles a day and I don't use those exclusively. I would be surprised if these wheels had 3000 miles on them.

Again, I am the 'King of Broken Spokes.'

This time it broke on the non drive side at the bend.

[marciero]

Originally Posted by redir

My idea is to buy 12 Strong spokes and rebuild the drive side of the wheel by removing one spoke at a time and truing up. Does that sound feasible? These are carbon hoops some 30mm deep or so, so they are pretty stiff rims.

This may have been mentioned but best to de-tension all the spokes, replace, then tension uniformly.

Originally Posted by unterhausen

But I really doubt you are going to rebuild one spoke at a time successfully without a tension meter.

It's not hard to show that your ear is roughly as sensitive as a tension meter for detecting relative tension. I gave an argument here a while back.

[redir]

I have built a few wheels before, or I should say rebuilt, using the Sheldon Brown method and he does say that using your ear can work. I never had a spoke tension meter. So looking at this tool:

https://www.parktool.com/product/spo...ion-meter-tm-1

What does it actually do? I mean... Is there a specific tension to build to for a gauge and type of spoke, rim depth or even brand of rim, drive side, non drive side, number of spokes and so on? Or is it you just lace up the wheel and then use this to make sure that each spoke is close to the same tension? And in the latter case why would that even matter? You need to make sure the wheel is true right? So you cannot simply tension to a specification because the rim might not be so perfect and then you need to tighten some more then others.

[GregL]

Originally Posted by redir

https://www.parktool.com/product/spo...ion-meter-tm-1

What does it actually do? I mean... Is there a specific tension to build to for a gauge and type of spoke, rim depth or even brand of rim, drive side, non drive side, number of spokes and so on? Or is it you just lace up the wheel and then use this to make sure that each spoke is close to the same tension? And in the latter case why would that even matter? You need to make sure the wheel is true right? So you cannot simply tension to a specification because the rim might not be so perfect and then you need to tighten some more then others.

- Some rims and wheels have specific, recommended spoke tensions. If no specific tension is recommended, 100-120 kgf for drive-side rear and front spokes is a good reference point. The non-drive-side rear tensions will be lower (unless using offset rims and/or hubs designed to minimize wheel dish).

- Yes, a chart is included with the Park tool that converts the spoke deflection reading to tension in kgf.

- You need to hit the "sweet spot" where spoke tension is uniform around the wheel AND the wheel is true. There will always be some small variances in spoke tension, but they should be minor provided the rim, hub, and spokes are manufactured to high standards.

- If the rim is not well made (i.e., nearly true when completely untensioned), you will never be able to build a reliable wheel. A wise bike mechanic once told me to lay new, unbuilt rims on a perfectly flat surface and make sure that they are laterally true before building the wheel. A good rim should build up into a true wheel with very little tension.

Greg

[redir]

Thanks Greg.

I just watched this video and the guy did a fine job of explaining it.

https://www.youtube.com/watch?v=XUqul03hbZ8

[Mark McM]

Originally Posted by GregL

- Some rims and wheels have specific, recommended spoke tensions. If no specific tension is recommended, 100-120 kgf for drive-side rear and front spokes is a good reference point. The non-drive-side rear tensions will be lower (unless using offset rims and/or hubs designed to minimize wheel dish).

Optimum spoke tension will depend on several factors, but the primary variables are rim strength and number of spokes. Sadly, rim manufacturer tension recommendations tend to be generic, and do not really represent optimum tensions. For example, wheels with fewer spokes need higher tensions, but often tension recommendations don't account for the number of spokes. Also, heavier (stronger) rims usually have higher maximum tensions, but many manufacturers have the same tension recommendation for all of their rims, from lightest to heaviest. The recommendation above for 100-120 kgf might be fine for an average rim, but it will be too high for a lightweight rims with many spokes, and too low for heavy stiff rims with few spokes.

Another issue is that spoke tension recommendations often don't account for dished wheel tension differentials. 100-120 kgf might be okay for average tension on a given rim, but because this is an average, it means the tensions may be higher than this number on the drive side. I often use about 140 kgf or more on the drive side, so that the average between both sides is not too low.

140 kgf drive side tension may sound too high compared to some recommendations you might hear, but you'll find that many wheel manufacturers agree also use similarly high tensions on drive side spokes. Here are some examples of published spoke tensions:

Campagnolo maximum drive side spoke tensions for several wheels that range from 125 kgf to 160 kgf:
http://www.campagnolo-sirer.cz/img/c..._2015-2016.pdf

Shimano maximum drive side spoke tensions for road wheels that range from 337 lbf (153 kgf) to 360 lbf (163kgf):
https://si.shimano.com/pdfs/dm/DM-WH0004-01-ENG.pdf

So, how do I decide on spoke tension? For lightweight rims, the spoke tension limit will be determined by the circumferential strength of the rim, and I've found through experience that the optimal spoke tension based on circumferential strength is a related to rim weight and the number of spokes. For 700c rims, by starting point for selecting spoke tension is based on this formula:

Average tension in kgf ~= 8 x (weight of rim in grams) / (number of spokes).

For example, a 420 gram rim with 32 spokes may have an average tension of about 8 x 420 / 32 = 105 kgf (for rear wheels, the tension will be higher on the drive side and lower on the non-drive side).

For heavier rims with fewer spokes, the circumferential rim strength is not the limiter, and instead, it is limited by either the strength of the rim spokes holes, or simply the build-up of friction in the spoke nipples at high tension. Depending on the robustness of the rim and/or the spoke nipples, I might limit the drive side tension to 130 kgf - 150 kgf. Since I typically use fewer spokes in the font wheel, I'll often use an average tension on front wheels of just a little lower than the drive side tension of the rear wheel.

[oldpotatoe]

Mark writes-

For 700c rims, by starting point for selecting spoke tension is based on this formula:

Average tension in kgf ~= 8 x (weight of rim in grams) / (number of spokes).

HA, never seen that before. Aluminum rim, I assume. Tried with a few examples and yup..what I shoot for..110-120kgf right rear/front..

450 gr rim, 32h...like an Archetype, DT460, Velcoity Quill, type rims..

BUT..for a 36 wheel vs 32h wheel..I'd still use the same tension..110kgf or so.

[redir]

Interesting discussion.

So I had a look at the Open Pro wheel that I just broke a spoke on. I took the cassette off and at first sight I immediately remembered that one time I had chain suck so bad it wrapped my RD around the frame and I had to release the rear skewer and pound out the rear wheel because the chain had got stuck between the spokes and the largest cog.

About 6 of the spokes got chewed up by the chain to where you could even see little nicks in the metal of the spoke and that is exactly where it broke. Not at the J-Bend but about 1/2 inch from it.

So I had another Open Pro wheel that I blew out the flange of the Dura Ace hub on some years ago and I 'borrowed' six spokes from that, laced them up one at a time replacing the chewed up spokes and now I am on the road again

We'll see how long this quick fix lasts.

[Mark McM]

Originally Posted by oldpotatoe

Mark writes-


HA, never seen that before. Aluminum rim, I assume. Tried with a few examples and yup..what I shoot for..110-120kgf right rear/front..

450 gr rim, 32h...like an Archetype, DT460, Velcoity Quill, type rims..

BUT..for a 36 wheel vs 32h wheel..I'd still use the same tension..110kgf or so.

If you tried using 110 kgf on a 36 spoke Mavic GEL280 rim (290 grams), you'd likely buckle the rim. Building wheels with ultra-light rims is what really brought home the compressive stress the spokes impart on the rim. The circumferential force on the rim from static spoke tension is roughly:

Circumferential force ~= [(Average spoke tension) x (Number of spokes)] / [ 2 x pi ]

So, 32 spokes at 100 kgf creates a compressive force of 509 kgf = 1120 lb. (By the way, this shows why welding is not necessary for a rim joint, and a sleeved joint can be just as strong - the compressive force from spoke tension is so high, that it is unlikely to that a sleeved joint will come apart in use). If you used 36 spokes at 100 kgf, the circumferential compressive force goes up to 630 kgf = 1386 lb. This is too much for many ultra-light rims.

Of course, now that rims are deeper and heavier than in the in past, and most wheels have fewer spokes, the circumferential load on the rim is no longer the limiter on spoke tension. Which is a good thing for tubeless systems, since the tight fit of the tubeless tire bead adds extra circumferential loading on the rim.

[Mark McM]

Originally Posted by redir

So I had a look at the Open Pro wheel that I just broke a spoke on. I took the cassette off and at first sight I immediately remembered that one time I had chain suck so bad it wrapped my RD around the frame and I had to release the rear skewer and pound out the rear wheel because the chain had got stuck between the spokes and the largest cog.

About 6 of the spokes got chewed up by the chain to where you could even see little nicks in the metal of the spoke and that is exactly where it broke. Not at the J-Bend but about 1/2 inch from it..

Notches on the spokes will create stress concentrations, and this can result in accelerated fatigue at the notches. Sharp kinks in the spokes can also cause stress concentrations, which can result in fatigue failures.

Originally Posted by redir

So I had another Open Pro wheel that I blew out the flange of the Dura Ace hub on some years ago and I 'borrowed' six spokes from that, laced them up one at a time replacing the chewed up spokes and now I am on the road again

It's usually not a good idea to re-use spokes, unless they can be used in the same position on a similar wheel. When spokes are laced and tensioned, the spoke elbow will get bent to match the orientation of the hole and the angle of the spoke from flange to rim. The act of bending a spoke can work harden the metal If the spoke is moved to a different wheel or position in a wheel, it may get bent again, often slightly in the opposite direction. Work hardened metal doesn't like getting re-bent, and may form micro-cracks if it is bent in the opposite direction. These micro-cracks can slowly propagate over many load cycles, resulting in fatigue failure.

[redir]

Originally Posted by Mark McM

Notches on the spokes will create stress concentrations, and this can result in accelerated fatigue at the notches. Sharp kinks in the spokes can also cause stress concentrations, which can result in fatigue failures.




It's usually not a good idea to re-use spokes, unless they can be used in the same position on a similar wheel. When spokes are laced and tensioned, the spoke elbow will get bent to match the orientation of the hole and the angle of the spoke from flange to rim. The act of bending a spoke can work harden the metal If the spoke is moved to a different wheel or position in a wheel, it may get bent again, often slightly in the opposite direction. Work hardened metal doesn't like getting re-bent, and may form micro-cracks if it is bent in the opposite direction. These micro-cracks can slowly propagate over many load cycles, resulting in fatigue failure.

I think maybe I did what you said without even thinning of it. The Dura Ace sacrificial wheel has the exact same length spokes and I pulled them out from the out facing flange holes to replace them on the out facing flange holes on the Ulterga hub.

I know it's not ideal but it gets me back on the road.

Unless you are saying it might not be safe?

[unterhausen]

It's fine, they just might break again. But I doubt it.

I was wondering how you were breaking so many drive side spokes, it's very uncommon.

[redir]

Originally Posted by unterhausen

It's fine, they just might break again. But I doubt it.

I was wondering how you were breaking so many drive side spokes, it's very uncommon.

I still do break a lot of spokes but yeah on this wheel it was quite obvious why when I pulled the cassette off. You could actually feel like a sharp tooth where the metal of the spoke got cut by the chain.

[oldpotatoe]

Originally Posted by Mark McM

If you tried using 110 kgf on a 36 spoke Mavic GEL280 rim (290 grams), you'd likely buckle the rim. Building wheels with ultra-light rims is what really brought home the compressive stress the spokes impart on the rim. The circumferential force on the rim from static spoke tension is roughly:

Circumferential force ~= [(Average spoke tension) x (Number of spokes)] / [ 2 x pi ]

So, 32 spokes at 100 kgf creates a compressive force of 509 kgf = 1120 lb. (By the way, this shows why welding is not necessary for a rim joint, and a sleeved joint can be just as strong - the compressive force from spoke tension is so high, that it is unlikely to that a sleeved joint will come apart in use). If you used 36 spokes at 100 kgf, the circumferential compressive force goes up to 630 kgf = 1386 lb. This is too much for many ultra-light rims.

Of course, now that rims are deeper and heavier than in the in past, and most wheels have fewer spokes, the circumferential load on the rim is no longer the limiter on spoke tension. Which is a good thing for tubeless systems, since the tight fit of the tubeless tire bead adds extra circumferential loading on the rim.

Don’t think I mentioned ultra light rims….nope, but if I’m using a 36h, 450g rim, I still shoot for the same tension as the 32h wheel. 110-120kgf.

[bob_in_pa]

Originally Posted by Mark McM

If you tried using 110 kgf on a 36 spoke Mavic GEL280 rim (290 grams), you'd likely buckle the rim.

Your specific examples are very interesting and relevant to one of my next projects. I found a single NOS Mavic GL330 hanging on a hook in my basement I didn't even know I had, it's probably been there 25 years.

Anyway it's been a long time since I've built a rim this light (330-350g?) and wonder what your thoughts are compared to building say Mavic GP4, which I've built regularly?

Its 36h and the plan is to lace it to a C-Record front hub. What would you think an appropriate tension would be? Your formula yields 74-78kgf depending on the weight of the rim (330g advertised vs 350g expected). My first thought is that seems low but I'm new to measured tension and a little out of practice.

Thanks,
Bob