conducting a study on how crank stiffness effects speed

[kbbpll]

I'm not an engineer and failed as a physics major, so feel free to disregard. As purely a "thought experiment", it seems to me that the spring effect would result in a loss of energy going into forward motion. Energy would go into the spring during the power part of the stroke, and then spring back when power from the foot eases. Since one end of the spring is bone and muscle, I would think your foot/ankle/leg would absorb the energy rather than it going into crank rotation. If, however, you did the experiment with a pedaling machine with a high degree of stiffness, I think the spring energy would in fact go into crank rotation, since stiffness at the pedal would remain more constant throughout the stroke. Well, it's fun to think about.

[istigatrice]

The Garmin vector sounds like an interesting product, hopefully cost won't be prohibitive on that.

With someone's suggestion earlier on of not using custom cranks and standard market cranks, what cranks are generally known to be stiff and which ones not so? I've read the fairwheelbikes crank shootout and I was hoping there would a crank that flexes much more than the cranks on test... does such a crank exist?

[basilic]

to follow up on djconnel, why not measure power both at the pedal and at the hub? the difference is what you wasted in the crank, chain, sprocket.

[djconnel]

Right -- that would be a good approach if you trust both power meters to be accurate enough.

On dissipation in the leg: the leg follows a certain trajectory with a stiff crank and a slightly different trajectory with a flexible one. I see no reason to believe one versus the other would result in more or less internal dissipation. For perfect stiffness it's a perfect circle, for flexy it would be slightly eccentric. But it's not as if the foot is stationary in one case (stiff) and moving in the other (flexy).

[eric]

I was hoping there would a crank that flexes much more than the cranks on test... does such a crank exist?

I used to use FSA carbon ISIS cranks which flexed WAY more than anything else I have used.

[djconnel]

I'll bet Rene Herse flex a bit:

[djconnel]

Here's the loser in the Fairwheel test:

[istigatrice]

@Juanmoretime, interesting observations there, with your days in multisport, where your competitors on similar equipment to you? It could just be that everyone was experiencing the same "loss" as you.

Also, what are people's opinions on the Look Keo Power pedal? Since I have a Polar computer this would probably be easiest, but I'm concerned by the accuracy of it