Damon wrote:
This is only true if loss due to tyre deformation is linear, which it isn't. You lose more energy from one deep deformation than from two shallow ones.
Why? The tyre carcass deforms more on large impacts, and a tyre loses energy each time it stretches and returns to a position (it's not a perfect spring, it has hysteresis). The most efficient system varies the deformation of the tyre as little as possible.
So suspension is better for rolling resistance.
Not true, radial deformation of tires doesn't exhibit hysteresis but it has viscous damping.
Tom A. wrote:
If you truly believe what you wrote above, then you have a complete misunderstanding of the sources of rolling resistance in a bicycle tire and how the pneumatic tire construction acts as the most "efficient" suspension you can get.
In short, you WANT the tire to take up the deflection because it can actually RETURN the energy (most of it...minus tire internal losses) back to the road surface in the trailing half of the contact patch. Use a tire with low internal losses, and "Voila!", you have low rolling resistance on ALL surfaces. Remember, it's the "torque arm" caused by the difference in energy absorbed in the leading half of the contact patch and the energy returned in the trailing half of the contact patch that is the source of rolling resistance.
In contrast, any energy that makes it "past" the tires (e.g. if they are too stiff) cannot be returned to the road surface as the tire does. It needs to be dissipated somewhere...either in the rider, or in a damper of some sort (i.e. read "beam"). That energy needs to be supplied by YOU to keep going forward. Sure, you may have actually reduced the rolling resistance of the
tire by stiffening it up,
but the total "resistance to forward" motion is overall higher.
Tom, I think you are mixing two concepts here: the effects of tire carcass stiffness in rolling resistance and the effects of reduced normal load in rolling resistance. Everything you have said here it's true but you have to take into account that Crr isn't constant for zero slip conditions. As you know, Crr depends of the pressure for a given load or, alternatively, it depends of the sinkage depth, the bigger the sinkage depth, the bigger the Crr.
A more compliant rear end can reduce the effective load in the contact between the tire and the ground and reduce the average Crr during the fluctuations of the sinkage depth. So we have to consider two aspects, the losses caused by the viscous damping and the variations of Crr of the tire and the losses caused by rear end's deformation. As you can imagine, there isn't an easy answer
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