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Old 08-14-2019, 11:02 AM   #47 (permalink)
aerohead
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math

Quote:
Originally Posted by RedDevil View Post
Of course. But not 65 times as much, and not linear to weight. Bigger wheels, relatively less contact area in the moving parts does reduce friction.

NO!
We are talking energy efficiency here. To move an object twice as fast the drag quadruples (as it is squared) and the distance covered doubles (as it is linear with speed). So you need 8 times as much power, but you cover twice the distance, hence the economy only suffers to the square.

Call them liars or accept their claim expecting they know their math better than we do. I hinge on the latter.
*If they're comparing the two vehicles,side-by-side,at the same velocity,and if the R-R coefficient were the same,from the equations I've got,then the rolling resistance would vary arithmetrically (monotonically?) as a function of (mass)weight.For instance,a doubling of weight would see a doubling of power to overcome rolling resistance,at any given velocity,up to the standing-wave velocity.
*If the R-R coefficient is different (and the skinny tires/wheels could certainly do that!),then that must be accounted for.
*At the same velocity,the vehicle's aerodynamic power requirement,should only vary as a function of the percentage difference in drag-factor (CdA),from one car to the other.A doubling of the CdA would double the aero- power requirement.(we've already accounted for velocity-cubed/power function).
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