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Old August 3rd 07, 06:58 PM posted to rec.bicycles.racing
Dan Connelly
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Posts: 451
Default Climbing seated on the hoods vs on the tops...??

Tuschinski wrote:

Nope, pure and simple aerodynamics. Another nice one: Aerodynamics
have more effect than weight on TdF cols. The speed of the pros and
the gradient make weight a much smaller factor. It's why the
Lightweight (German Brand) wheels are popular, light AND aerodynamic.
The big disadvantage is that high rims are pretty unforgiving. Using
them 6-7 hours is very uncomfortable, even for most pros.

It's also one of the reasons why drafting behind a teammate still is
important in the mountains.


Wind resistance: 1/2 rho Cd A v^2, where rho ~ 1.1 kg/m^2, Cd A ~ 0.3 m^2
Mass-proportional force: M g (grade + Crr), where Crr is rolling resistance ( 0.6%, typical), M is total system mass (75 kg, typical), g is gravity (9.8 m/sec^2)

These are equal for:

v = sqrt [ 2 M g ( grade + Crr ) / (rho Cd A) ]

For example, a 7% grade: 19.3 mps = 69.5 kph

So if you can climb a 7% grade at 69.5 kph, then wind resistance is contributing as much as weight....

One issue with these wheels is due to the UCI limit, there's no advantage (except during some accelerations) to lighter wheels, since weight would need to be added somewhere else. That said, whether they are worthwhile depends on the relative advantages to wind resistance and weight; there's no magical grade at which weight becomes always more important.

Dan

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