carbon seatstays + aluminum frame - Page 3

But Alu aren't much better when it gets a hard ding.

Recently saw a forum discussion on the value of that silicone Zert insert seen on Specialized bikes. This guy is just adamant that it works, and the "great ride" was all attributable to the silicone.

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Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac

Yeah, i can feel a differance in the bikes, of coarse you have to add those factors in, but I'm sure material plays a role in it, no matter how significant it is, it does play a role

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“(Training) doesn't get easier; you just get faster”
-Greg Lemond

I say "hypothetically" is your most important word because you are only offering opinion - you say Cf frames or stays "do not" or Al "is not" - with no evidence at all.

I could cut and paste your argument and simply take out all the "nots", leaving an argument that is just as valid - but in support of cf stays reducing "bumps".

I do not necessarily disagree with you, but hey - show me the money.

The crux of my statement is this: a rear triangle does not realistically deflect in the vertical plane regardless of material.

Following on from your last comment, you are saying that this is equally valid: a rear triangle does realistically deflect in the vertical plane regardless of material.

Why then is it the case that few/ none of the frame testing services try to test rear triangle vertical deflection under load, if it is a frame variable? This is from Damon Rinard, an engineer and frame tester working in the cycling field and endorsed by Sheldon Brown: "I ignored any vertical loads on the frame, as I believe a traditional diamond frame resists such loads easily due to its truss design in the vertical plane."

One of the indices of a material's merit is the modulus / density, which is a good measure of a frame's stiffness if they are all built to approximately the same tube weight and tube diameter (which they are not). CF gets 54 MN m /kg, while Al gets 25. This means that CF is stiffer than Al, and is less likely to deflect than Al, even if we accept that there is realistic deflection of a truss structure (which I do not accept).

In summary, I would say 1) a rear triangle does not deflect vertically to any realistically detectable extent and 2) even if a rear triangle did deflect realistically, a CF rear triangle is going to deflect less than an Al one, given similar tube diameters and tube weights.

Happy?

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"All that we see and seem is but a dream, within a dream..."

Well, it's a very small role in comfort, and it's guaranteed that there's no way to say that the two bikes you mention ride differently because of material differences. Can't be done.

unrelated: have you seen these 'piss-take' reviews by Bike Snob NYC?

Funny(ish)

http://bikesnobnyc.blogspot.com/2007...-shootout.html

As I said, I think, already, Bill Holland--a well known custom frame maker here in the US--tested various rear triangle configs on bikes and found in all cases that the seatpost deflected more than the rear triangle. He said rear triangle deflection in the vertical plane was virtually non-existent.

You only gave them funny(ish)? They're only not funny because they are substantially the same as gets written in the mags.

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"All that we see and seem is but a dream, within a dream..."

Yes I have. The man does funny stuff. You gotta keep tunin' in, 'cuz invariably there's a belly buster right around the corner.

The man do make me laugh. Nothing makes a day more sunny than a good piss-taking.

Then, there's this.

OK I'm getting into this one late, but not really taking side, rather asking a few questions.

If a rear triangle does not deflect in the verticle plane, then why do most roubaix special builds have longer stays? I thought the theory was better stabily in the rough and more compliance for comfort.

Also since carbon fibre lay ups can be designed to have directional stiffness, and less prone to fatigue, surely a carbon fibre rear triangle can be designed (by a good designer) to be laterally stiff, but give more compliance in the verticle plane? That must also apply to carbon stays on Al front triangle. CHances are these bikes are usually cost optimised rather than performance optimised though.

I was also of the understanding that an Al frame could be made as light as LW carbon, but wouldn't be very stiff or strong as the tube diameters and wall thicknesses would be too small. Also a steel frame could be designed as stiff as an Al frame, but would be heavy as the tube size would add too much dense material. There is also 953 stainless which builds frames under 1000gms, but it flexes like a noodle.

From my understanding, you can use any material to get any one desired property, but carbon gives the opportunity to mix these often conflicting desires more.

I would love a carbon fibre bike, but considering the cost of quality carbon, and my belief that I shouldn't ride what I can afford to crash, I'm more likely to go custom steel or maybe full Al, and have a good carbon fork and seat post and wheels. I'm going to look to optimise the ride comfort with things other than the frame, but concentrate of body comfort with geometry.

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Precision Sports

pissa!

The stability effect comes from the longer wheelbase. Whether there is any real comfort effect, who knows? Whatever the stay length, it is still a truss structure.

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"All that we see and seem is but a dream, within a dream..."

They could, perhaps, if the rear triangle were not a truss. The vertical compliance thing is real marketing BS, except, of course, for the fork.

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"All that we see and seem is but a dream, within a dream..."

True, as I understand it. Strength is not really relevant, as frames don't get loaded to more than a small fraction of yield or breaking stress. Stiffness depends on your needs, but a superstiff bike is not necessarily faster than a slightly noodly one. The problem with your light Al frame would be fatigue, as the stiffer they are, the slower they fatigue.

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"All that we see and seem is but a dream, within a dream..."