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ULTRA-STIFF bikes, carbon rim, sprints =====> real questions(10 posts)

ULTRA-STIFF bikes, carbon rim, sprints =====> real questionscyclomoteur
Oct 30, 2001 5:48 PM
First : we need to know if stiffness increases acceleration when hammering the pedals in sprints.

Second : Do carbon fibre rims, such has Zipp 280, has lower degree of stiffness then Aluminium deep V's rim, such has Velocity Deep V ?

Third : If stiffness increases accel., do a racer need to get a 20lbs ULTRA-stiff bike or the advantage due to stiffness is too low to justified that gain of weight (assuming that boosting stiffness = boosting weight of components)?

Let's resolve the "stiffnesses" questions once and for all : Everybody would appreciate a scientific proof to justified your writings !

-Guillaume
That's tough,TJeanloz
Oct 30, 2001 5:56 PM
1. Yes, a laterally stiffer bike will accellerate faster. The stiffer the frame, the less energy is lost in a side-to-side direction, hence more in the front-to-back vector.

2. Not necessarily. A carbon rim can be very stiff, and an aluminum rim can be quite flexy- there are other variables, like spoke tension, hub flange height and spoke length that effect overall wheel stiffness.

3. A heavier, stiffer frame might help acceleration; but a heavier, stiffer wheel will hurt acceleration. More mass at the rim of the wheel requires more energy to accelerate. With wheels, there needs to be a balance between weight and lateral stiffness.

If the stiffness question could be resolved, it would have been already. Different people have different stiffness requirements, and as such, the question will never be fully answered.
Ask a sprintercyclequip
Oct 31, 2001 6:20 AM
Instead of wanting scientific proof, why not ask a sprinter?
I know Eric Zabel prefers stiffness over all else!
Stiffnessbrider
Oct 31, 2001 9:14 AM
I remember an interview with Ken Carpenter (America's premier track sprinter before Marty Nothstien), and he talked about his bike quite a bit. Basically he called it a "girder on wheels", stiffness above all else. Steel frame, made ultra stiff, 40 spoke wheels so tight the spokes would pucker the rim. Of course, he was a very big guy, extrememly strong, would tear apart a normal bike in very little time, and didn't ride hills.

You kind of have the same considerations for stiffness as a climbing bike -- more stiffness means more power to the wheel. Also, spoke tension is going to be a big factor to wheel flex. Rim depth will give the wheel more vertical stiffness, but the side-to-side is still determined by spoke count and tension.

Talking frames, the configuration of the bike will make more of a difference than material (and consequently weight). C'dales are pretty light, but also very stiff due to tube configuration. The flip side of that is if you have such an ultra stiff bike, it's going to beat you up pretty badly and fatigue you before you get to the finish line. There's a balance to achieve here, and usually you find it over years of riding and trying different things to see what works best for you.
re: ULTRA-STIFF bikes, carbon rim, sprints =====> real questionsEric
Oct 31, 2001 9:18 AM
I don't know of any real world data for Q#1.

For Q#2, I'll defer to the following:
http://www.sheldonbrown.com/rinard/wheel/index.htm

For Q#3, the question is whether one is trying to achieve a fast bike for sprinting which will never be needed for climbing, or whether one is trying to balance stiffness and weight for the overall effect. A very stiff 20+ lb bike might be slightly advantageous in a very flat, very fast race. But it will be a liability if the race has climbs and/or accelerations from slow speeds because of its weight.
read thisJohn Brown
Oct 31, 2001 10:34 AM
http://www.bontrager.com/keith/rants.asp?id=32
read thisTJeanloz
Oct 31, 2001 12:21 PM
I slogged through 5 pages of a Keith Bontrager rant, something I almost always hate to do, and didn't come out with any more knowledge than I went in with. I will paraphrase his 5 pages of muck: "stiffness is too complicated for you or me to figure out." I agree, it's damn complicated. His problem was that he didn't really have a thesis- or the thesis he wanted to have "Stiffness doesn't matter" turned out to not be provable.

He argues quite well that the cumulative effects of flex might be very, very small; but he is unable to say that there is no effect- because there is one. He is at most able to say: "there is an effect, but dude, trust me that you can't tell."
read thisCyclorocket
Nov 1, 2001 3:27 PM
I don't like Trek services so I don't like to read their bull$hits, but I reed on... I agree with out : what tha hell is he talking about...tell your point o shut up !!
Keith ... I've lost my time with your writings
re: stiffnesss and accelerationguido
Oct 31, 2001 1:34 PM
Yes, stiff bikes transmit intense pedaling to a straight line on the road. But the bike doesn't have to be super stiff all around, unless you're a big heavy rider like Marty Nothstein.

You need stiff wheels, bottom bracket and chainstays. A little vertical flex can be tuned into the frame and fork for comfort, that won't affect acceleration, as in a sprint for example. Only big massive riders need really stiff frames to handle the weight of their upper bodies. Torsional loads on the crank from pedaling are handled by the bottom bracket and chainstays, mainly.
Ask Sean KellyKerry Irons
Oct 31, 2001 5:14 PM
He won the TdF sprinter's jersey several times, along with a load of classics, on an Alan aluminum bike. The Alan was probably one of the flexiest frames every made in the modern bike era. No special alloys, and small diameter tubes. Yes stiffness is important, we just don't know how, when mixed with all the other factors that enter the equation.