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Isn't the force applied to a disc rotor greater than that applied to a rim?
If a wheel has to stop in say 1 turn, then that is roughly 2 metres long at the rim, but a lot less at the rotor, which means you need more friction at the rotor, hence more force...Am I talking nonsense here?
ugosantalucia-
Am I talking nonsense here?
No, you're quite right. In fact, if you want to bandy apparently impressive numbers based on an oversimplification, the total shear load on the rotor bolts is about 15 times that on the rim brake pad bolts. However, the question isn't "how big are the loads on the braking components?", it's "how big are the braking loads on the spokes?"
gbj_tester
I'm not assuming they don't, I'm just countering the frequent assertion that there's magic involved in rim-braked wheels which somehow allows braking to occur without affecting the spokes, and that by contrast everything which happens to the spokes under disc-braking is the fault of the torque applied to the hub by the rotor.
What is certainly different is that brake loads from rim brakes are shared equally between the left and right sets of spokes, but disc brake loads bear more heavily on the rotor side. This makes me wonder whether the aero bike makers ought to consider two discs, as each could be smaller than a single disc, and halving the torque load on the rotor side would permit a lower spoke count.