Chainstay philosophy?
 

I have a weird topic that I was thinking about during the break in March Madness. My wife has basically given me the green light to get a new frameset in the next year sometime. I have 58 fierte that I really like, but sometimes I have illusions about my abilities and long for a race bike. It was a sunny but cold day in Michigan, so we went looking at some different bikes. I have the green light to spend about 3 or 4 grand. I've been to the Serotta dealer numerous times and am considering a custom concours that is a little racier. We also went to the Orbea dealer to look at the new Orca. What a jaw dropper. The guy offered to sell me it in a 57 for 2340 dollars. That is frame fork and headset. I explained I was just looking at then we went to the Seven dealer. I was looking at the Seven's (most of which were signature series) and noticed on every single one had much beefier chain stays than the Fierte. I didn't think I was imagining things, but it seemed pretty obvious to me. My question is there a chainstay philosophy, and what do differently designed chainstays offer. The Seven chainstays were very stout. I weigh about 200 lbs on the nose, and got wondering if I would like the ride of a bike with a thicker set on chainstays. The Fierte's stays are on the long side (42cm) so I don't know if that is a factor in what I was perceiving. I also looked at alot of Cannondales, and other "race bikes' and those stays were a lot beefier as well. I know the chainstays are only one component of the bicycle, but do different manufacturers have different ideologies about the stays. I was reading some of the reviews on pez cycling and the author test rode a Seven (I can't remember what model) and they gave him oversize stays. He asked Serotta for the same, and they rejected his idea. They built him a bike with normal stays that was exactly what he was looking for. Both bikes were designed to be very stiff race bikes. Any ways back to my question. Do different manufactures have different ideas, and what are benefits or weaknesses of each design.

Hey,

This is a favorite subject of mine.

I'll say up front that I have no idea what bike you might like best. I'll leave that alone.

First I'll say something that you won't hear from many builders.......curving or bending the stays into any configuration other than straight will make the stays flex more. There are very few absolutes in life but this is one of them. Curved stays flex more than the equivalent stay without the bend. They won't flex a lot more......just a little. It depends on the type of bend and the degree of bend. One thing is for sure, the bent stay can never be stiffer due to it's bend. The biggest reason to bend a stay is to allow for better clearances with tire and chainring. This is a bigger deal on mountain bikes than road but true nonetheless.

In any given material, stay diameter is the biggest factor in determining the stiffness. The bigger the diameter, the stiffer the stay. The problem is that if you make the stay bigger in diameter you run into clearance issues with both the chainrings and tire. So..... most stays are about the same in this regard. One can use huge stays (Big Leg Emma) but then you need big, deep dents to allow for the clearance room and the dents go a long way to negating the gains in stiffness made by the larger diameter stay.

There is a current trend in frame design to control BB flex with a big-arse downtube. This may feel like a good thing at first and it will certainly help with front derailer rub but in the end it does not make for a stiffer bottom bracket. It's often overlooked but it's the chainstays that make the drivetrain stiff. A big downtube might be good for other reasons but it doesn't do squat to make for a stiff drivetrain. A Slingshot frame is a great example of this. It's simple when you think of it. The energy goes into the frame at the BB and goes to the rear wheel.........and the only thing between the BB and the wheel is the chainstays. This is one of the big issues in designing a good Ti bike for a big or heavy rider. Titanium is much more flexible than steel. The way to make it as stiff as steel is to make the diameter much larger. But this has it's own clearance issues. So they make the stays oval (making them stiff in the vertical direction and soft laterally.......not ideal) or they put in huge dents which has it's own issues. So most Ti builders compensate for the wimpy stays with a huge downtube. And like I stated above this has little effect on true drivetrain stiffness. This is one of the reasons that many larger folks feel that Ti bikes don't have the snap they are looking for and why it's fallen out of favor with many racers.

When pedaling a bike out of the saddle chainstays are asked to do a number of different things. They undergo compression which is easy for almost any stay design to deal with as the loads are low. They undergo a torsional (twisting) load which most stays deal with fairly well regardless of shape. Larger diameter helps a good bit with the torsion. The other thing that happens to stays is that they see a lateral bending load as the BB is pushed from one side to the other. This is where ovalized stays can get in trouble. An oval tube has a major diameter and a minor diameter. There is a pretty good rule of thumb that addresses how an oval tube will flex compared to a round tube. The oval tube will flex about the same as a round tube that has the same diameter as either the major or minor diameters of the oval. In other words if you have an oval tube that is 30mm by 17mm in cross section it will flex about the same as a 30mm round tube in one direction and about the same as a 17mm tube in the other direction. So if you think of oval chainstays you in effect get the lateral stiffness of a rather small round tube.

For all the above reason I feel that a round stay is best. You get the most bang for the buck in ever direction. You get good clearances with minimal denting and you get a nice stiff stay and drivetrain.

Wow............that's more writing than I thought it would be. Thanks for sticking with me.

Dave

Dave,

Super engineering description on the role of chainstays. Enjoyed reading it. Keep writing.

Back to March Madness. Go Bucks!!!

Thanks
 

Thanks for the education, waiting for my hat and my first ride on my Terraplane!

Henry

My Cannondale has pretty beefy chainstays. I always wondered how stiff the BMC SLC is.

snipped

Wow, I wonder what Ben would say about this. His marketing literature from years past indicated otherwise.

Regardless, great post Dave.

wonderful post on the subject.

My experience with a famous brand ti frame is that it's true, the material doesn't have that "snap" you're describing, but I only see that as an issue if I were racing crits, and it looks like I don't do that much anymore. Otherwise, I think the flex is pretty nice to have.

I remember in the 70's, lots of French bikes had round stays with all kinds of dents and crimps, and the whole purpose of going to oval was to escape that crimping. . .

there's such fiery arguments about straight vs. curved forks, it makes you wonder why we don't have similar interest in the disposition of the rest of the bike.

Thanks
 

Thanks for the info everyone. Your responses are worded much better than my question was. Thanks again

Concerning the BMC, they flex. They are not known for being real stiff. Comfortable ride though.

one other factor worth considering is the drop-outs. if the stays taper down to nothing around the rear wheel save a piece of stamped aluminum a fixed to the seatstays via an m4 bolt the fatest chainstays in the world aren't going to be any better than anything else. part of what makes a pegoretti or a serotta legend ti such wonderful bikes while cornering hard and descending fast is the meaty drop-outs.

in the mountain bike world through-axles are employed to stiffen up the rear ends on downhill and freeride bikes for the same reason.

obtuse

Word.

Dave

I think Dario Pegoretti said more or less the same thing when he came by Austin a week or so ago...in fewer words. :D

Round is good.

In Italian? :D

No, Round is great.

Being Round makes the world go Around. :D Yes

Great post Dave. Thanks.

Kevin

Truly excellent stuff, Dave (and Obtuse) ... really made me rethink things.

Extended a bit, this also helps to explain the thought behind the Terraplane system (if I am not mistaken) - straight round chainstays/bend seatstays.

That funky looking rear triangle is suddenly looking a lot more attractive to my old bones and young heart.

Dave - I think you just pushed my next bike from Ti to Steel.

Obtuse - I think I get what you're saying about the dropouts, but wouldn't some of your concern be alleviated by the axle? Essentially the rear hub (with axle) makes a triangle out of the rear end. Or not. Can someone please educate me here?

Thanks, in advance!

You are correct in that the rear axle completes the triangle but unfortunately the axles, and more importantly their interface with the dropouts, is pretty wimpy. The 10mm axle standard should go away but I doubt that will happen anytime soon.

If the rear axle was say 20mm in diameter, you could make a very light, very stiff set up.

Dave

I don't know much about this standard, but I think the traditional BB standard should go away too. Cannnondale and Specialized have a larger standard. It seems to me that the new outboard BB bearings and the associated crank designs are full of compromises forced on the component manufacturers to work around a standard size BB shell which came into existence 50 or more years ago.

Thoughts on that too?

Anyway, this is a very interesting topic. I have also always been told that stiffness comes from the downtube. It is interesting to hear other thoughts on that. This is the reason this is such a good forum. Keep it coming!!

I'm not sure I ever equated dt stiffness with drivetrain stiffness.

I have a match Paramount with a big-*** downtube, and slightly bent stays, and the feeling is that there's some flex in the fork and rear end, but the wheels are connected in line. As opposed to some bikes with more of a hinge in the middle. Now, were I to get David or someone to build a custom, I doubt I would specify big oversize tubes like that; enough is enough. But it's not really a bad thing, either.

I think the better builders were always wise to the issue of drive-train stiffness (or "snap"). Many would substitute SP chainstays (and dt) on Columbus frames built for competitive riders, who never cared much about weight in those days.

Ouestion
 

Do the oversized chainstays cause (contribute) to the stiffness that gives a bike that "Pocket Rocket" out of gate fast acceleration be it for real or a feel?

All this talk about changing standards bothers me.

Considering how little coordination there is between the various players in this game I suspect that changing "the standard" will actually mean no standard, with everyone going their own way 1) as a marketing gimmick so they can claim that theirs is better than the other guy's and 2) so the user (that's us) is locked in to a particular system with no other options. All of this to shave a few more grams (and a very small percentage of the entire system's weight).

Louis

Dead on the money!!
 

Dave:

Thank you, thank you, thank you!!

For years, I have taught young builders, others in the industry and even competitors exactly what you bring up here. Some got it but most just kept at the down tube fixation. Granted, the down tube can offer a bit of lateral stiffness, but only from the bottom third of it’s length. (Headset bearings do not make much of a fixing point). Yes, down tubes can also offer some torsional help, but they are not very well fixed at their upper end.

Chain stays, on the other hand are oriented exactly in plane with a “fixed” structural member (the rear axle). They tend to be relatively short as well, plus there are two of them. What a gift! If one is looking for the ultimate in mechanical efficiency, a straight chain stay is ideal. “The shortest distance between two points is a straight line” and a longer stay is going to be more flexible.

As noted, clearances are almost always an issue here though. Joe Breeze used to call chain stays the most dimensionally challenged tubes in a frame. That is what he was talking about. You have to fit the chain stay between the tire and a chain ring somehow. The wider the tube section you can get in there, the better.

As others have noted, there have been a number of ways to squeeze things in there over the years. Currently, most manufacturers use some sort of combination of artful bending and ovalizing or dimpling. When Shimano and eventually Campy went from 8 to 9 speed, the front chain lines went outboard, giving us a few more mm to work with. Since then, it has been much easier to use less of whatever clearance technique we were using back in the day. Merlin’s 7/8" stays used to have that curve just behind the chain rings for just that reason. When nine speed chain lines became standard, we switched to straight stays since we had no need to bend them any more.

Now, with one inch stays, Merlin and we have taken two somewhat different approaches. Because our frames are all custom, and we know what cranks, rings, tires, etc. each of our customers might be using, we leave our stays straight and dimple only as much as we need to, but no more. Merlin, on the other hand has to satisfy a “stock market.” (Mostly) They do the curving and dimpling thing so that their owners can use Campy 44 tooth rings with large 25mm tires. They also concern themselves with the occasional size 46 foot.

Obtuse: Yes, Yes! Rear dropouts are just as much part of the structure. That space between the rear end of a chain stay and the rear axle is very important. Trying to save weight or look cool in there is counter productive.

You guys have no idea how happy this thread has made me this Sunday afternoon. Now, I am off to do two hours on the trainer ... Well, you can’t have everything on a Sunday afternoon, huh? ;)

Give Cannondale a couple of years. Then we'll have a "lefty". Can't wait to hear about all of the benefits!

-Ray

Joe Breeze's Breezer Lightning circa early/mid 90s

Very cool stuff ... thanks again to all.

I http://files.myopera.com/operadesign...684/LBughe.jpg Dave-

jason

That's creepy........have you forgotten about the restraining order?

Dave

Exactly. That rear axle is held in the dropouts by the equivalent of of one 5mm screw. Bolted axles make a huge difference in rear end rigidity. Another reason why Phil hubs are so cool.

This is a great forum.
 

I repeat - this is a great forum.

Jim

gradient butted, optimized shaping, tire clearance, heel clearance, and stiffness. You can have it all. :banana:

Just another data point
 

I've got nothing to add from a technical perspective, but wanted to throw out my experience riding Sevens, Serottas, and a Pegoretti.

Every Serotta I've ridden (Fierte Ti, Legend, Legend ST, Concours, and Nove) climbs better than every Seven I've ridden (Steel Axiom and Alaris.) Sevens are softer/deader. Serottas are responsive and react nearly instantly to the pedal. The Pegoretti Love #3 is a bit better in this regard than the Nove.

These designs all include round stays, but with very different designs. And the Serotta and Peg dropouts seem much more substantial than the Seven dropouts.

Hey TK , I assume we'd be better off with a longer stay then a carbone seat stay if we wanted compliance ...yes ?

why does everyone want "stiff"? personally, i think overly stiff frames are overly-rated. a little "squish" is not a bad thing.

I love this place...
 

So cool to have true masters of the craft answering questions from the masses. Seriously, I learn something every time I log in here.
When I was looking for my last bike it was down to either a Seven, a Roark and a Hampsten/Moots ti (I didn't know much about Serotta then; knew about Hampsten, knew about Roark, but not Serotta...go figure). Seven and Roark made much to do about their beautifully sculpted chain stays, but somewhere in the back of my mind my undereducated brain just "felt" that the straighter, 7/8 in round stays of the Moots welded to Wright/Breezer drop outs were more "right". Glad to know that I guessed right. To my mind the idea of welding that round tube to the Breezer drop out would make the most difference. Never could figure out why you'd want to have a big pipe then taper it down to join to an obviously "flimsier" (probably a misuse of the term here) drop out. But then again, I'm a pilot, not a materials engineer. Love my Hampsten/Moots and its cool to find out one of the reasons why!

Shawn G.

+1.

It is not like everyone is as strong as Lance (juicy or not) or as heavy as a NFL offensive liner.

You beat me to the punch....

In thinking about this thread, I had a good look at my Moots Vamoots and between what Obtuse and DK said, it truly looks like Moots just nailed it with their chainstays.

I remember reading somewhere where someone was "putting down" Moots by saying that they were a MTB company that makes a road bike now and again...Well, I am so glad that they took their design cues from the MTB world as they did a fine job on the Vamoots.

Steve

My first bike was a TCR1. I felt like when I stomped on the pedals, that it reacted like there was a fluid "torque converter" between me and the ground. (I'm using car analogies here.) IOW, it felt like pressing the gas on an automatic car.

On my Six13, when I stomp the pedals, it gets up and goes like a stick drive car, with real low gearing. Instant forward motion.

I don't know why there is this difference, but I like the Six13's response better. (The TCR was also a bit noodly at the head tube as well.)

I've been told if you can hear someone "screech" their tires on each pedal stroke on a steep climb that is because their frame is flexing to the point the tire isn't tracking straight any more. Truth or fiction? I dunno.

I assume this is what everyone means by stiffness. Maybe I'm wrong. Or something.

More likely too stiff and bouncing over undulations in the pavement-like my old cracknfail.

Smiley:

You actually have two issues within your question. A) Seat stay length and/or degree of straightness and B) Stay material.

A) The length of the seat stays per se will in theory effect compliance, but within the length range of real world seat stays, the difference is so slight that we can all forget about it. Effectively, straight tubes just don't compress enough to make any difference. When it comes to straightness, there are effects to be had. The Terraplane is the most obvious currently produced example of this technique. Our exalted host has also gone this route, but the general technique is VERY old. Nothing new under the sun. Most current road bikes now have some sort of curved seat stays. The curving allows the stays to flex somewhat like a leaf spring. Do you really get something? In general, all other things being equal, the answer is yes, but in order to get a really significant amount of vertical compliance from non-mechanical seat stays, you do need to do something like Dave has done. Do our "Mae West" style stays do anything? Glad you asked ... yes, we can measure it quite easily. BUT, unless you have two otherwise identical bikes to test side by side, the difference is subtle. Does it work in any other way? Glad you asked ... yes, they look beautiful to the poor guy you just blew by.

B) Materials; Here things get really sticky. Once you get into composites, the number of variables skyrockets. In general, the distinctions between straight and curved shapes have similar effects on compliance, but when you are working with curved composite stays, the actual materials used, amount of the materials and the layups have huge effects as well. In general, the higher the mass of a composite stay, the better it will dampen buzz and the heavier it will be. let me give you an extreme example; You have two wishbone stays which look exactly the same and measure out to have identical stiffness numbers. Wishbone #1 utilizes a low modulous carbon fiber material and wishbone #2 utilizes a hyper modulous material. Because of the differences in the stiffness of the materials, #1 will be quite a lot heavier and will dampen fine vibration more effectively. It will be a bit tougher in resisting impact as well. Since composite wishbones like most composite structures are hand made, there is always some variation between examples.

So ... if you want compliance, actual vertical movement, you need stays that allow the rear dropouts to move vertically. Seat stays which curve to some degree and are made out of a resilient material are the best way to do this, this side of a suspension rear end. This can be done with composite stays, but the degree of flex is quite difficult to control.

Hope I have not thrown too much up on the board. :cool:

U DA MAN TK and I'll keep my Hors Categorie bike thank you :banana: