Originally Posted by
john m flores
I just looked at my data on this same descent from 2014 on what I think was my 650c Serotta - max speed 40.5mph (65.2kph). So ~1.7mph faster on a bigger-wheeled bike.
This confirms what I've been thinking, smaller-wheeled bikes don't descend as quickly. Is the reduced rotational inertia? Or something with the aerodynamics of smaller wheels spinning faster? Frictional losses in the faster-spinning bearings?
I've only recently learned that smaller wheels and tires are less efficient overall even with the aerodynamic bonus.
I think it's due to the contact patch.
The smaller the diameter, the shorter distance the contact pressure increases over a specific distance.
(Smaller tire, less eccentric the oval shaped contact patch)
((so the tire has to deform more going from more round to contacting flat))
I think, with a skinny enough tire and high enough pressure, the deforming loss no longer negates the mass and aerodynamic advantages.
Then the ride would suuuuuuuuuuuuck.