Chainstay philosophy?

[davids]

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.

[Smiley]

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

[Samster]

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

[Moosedryvr]

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.

[Johny]

Originally Posted by Samster

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

+1.

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

[SoCalSteve]

Originally Posted by Moosedryvr

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.

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

[Xyzzy]

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.

[soulspinner]

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

[Tom Kellogg]

Originally Posted by Smiley

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

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.

[Smiley]

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

[Tom Kellogg]

Originally Posted by Smiley

... and I'll keep my Hors Categorie bike thank you

There you go. Good choice.

[J.Greene]

Originally Posted by Tom Kellogg

There you go. Good choice.

Tom,
intuitively i'd say this applies to forks as well, but i've heard that straight forks are not any more harsh than curved forks. I'm curious of your understanding because this subject comes up from time to time.

JG

[Tom Kellogg]

Originally Posted by J.Greene

Tom,
intuitively i'd say this applies to forks as well, but i've heard that straight forks are not any more harsh than curved forks. I'm curious of your understanding because this subject comes up from time to time.

JG

JG:

You would think so, but it is really not the same thing. Yes, all other things being equal, a curved fork blade is in fact longer and therefore more flexible. But forks flex quite differently from seat stays. Picture it this way; rear dropouts can not move fore and aft since the chain stays prevent that movement. Since most of a front dropout's movement in response to road shock is fore and aft, most of the actual flex in a modern fork comes from the top third of the fork. The paradox is that ideally, we want lots of longitudinal movement of the dropouts on rough roads, BUT we don't want them to move in the same way when we are braking hard on descents. In theory, that is the advantage to a steel blade style that was typical on British and French bikes in the fifties and sixties (and Paramounts of the early seventies). The upper part of the blade that gets the most force during braking remains pretty stiff but that sharply curved lower portion of the blade can still allow the dropout a bit of vertical movement. At least that is the theory.

All of that is out the window with modern composite forks though. Dimensional section and materials determine the way composite forks work now. Straight V. Curved composite forks is a complete red herring from a functional point of view. Go with the fork that works properly for you and if need be, tolerate the appearance.

[David Kirk]

Originally Posted by Tom Kellogg

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.

Now it's my turn to say thanks. It feels good to know that someone of your caliber agrees. Thanks for stating your opinion.

Dave

[Ray]

Originally Posted by Xyzzy

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

First off, lemme join the chorus in saying THANKS to Tom and Dave and Obtuse and others for a most interesting, illuminating, and educational set of posts.

Second, lemme just say that this post has mostly been about REAL changes in stiffness, compliance, etc. But I think there's also a PERCEIVED change based more on the length of the stays than anything else. Grant Peterson pushes this view a lot and I fully agree with him on this one. All else being equal (which, of course, all else never is) bikes with shorter stays FEEL quicker, stiffer, more like a manual tranny car. Which I think has more to do with the side to side movement induced by the pedal stroke than with anything else. This lateral movement is so instantaneous it makes it feel like the bike is reacting more quickly. But I don't believe it translates into more or faster forward movement, just the perception changes. Grant had an article about this in an early Riv Reader. He compared a bike with radically short stays (I think there was a split seat tube to allow the rear wheel to actually come forward between the two halves of the seat tube to a bike with real long stays. The bike with long stays could be stomped on with no perception of lateral movement - the bike with the radically short stays felt like you were making a u-turn with every pedal stroke. Didn't make the shorter stay bike any faster, but it sure felt different. Real world differences are smaller and the perception more subtle. ATMO contends that you'd never feel a difference of 1 cm and I can't argue with him. But my old RB-1 and my '97 Riv were just about identical bikes except the Riv had stays that were about 25 mm longer and I could damn-straight feel the difference there.

Anyway, just sayin'

-Ray