Originally Posted by
dougmc
Qualitatively, you are correct -- mass on your wheel has a larger impact on your total inertia than mass on your frame (or your body.) But qualitatively, you're wrong -- mass at the outer edge of your wheel, no matter what its radius, only counts twice as much as mass on your frame or at the hub.
Mass at the hub is close enough to the center that it counts approximately as much as mass on your frame, but mass at your rim and wheel is close enough to the outer edge of your wheel that it counts approximately twice as much as mass on the frame.
And note that this is only about inertia -- accelerating and deaccelerating -- not climbing. For climbing purposes, it doesn't matter where the mass is on your bike, it has the same effect.
And yes, in general the only time that such things are really important is during a race. A few lbs extra on the bike really only matters when 1) every second counts (i.e. a race) or 2) if you're carrying the bike. But if it is a race, it's better to have the weight on the frame or hub than at the outer part of the wheel.
I don't see where you get that the force required to overcome inertia due to mass at the rim is twice that needed to overcome inertia due to the same mass on the frame. Can you explain that? I have reviewed my math and concluded that my factor of 66 was correct for moment of inertia, but not for the force required to accelerate the wheel, driving it from the hub. I think the force required is actually half:
F_applied = (total_mass_at_rim x bike_acceleration)/2.