Thanks for the clarification RChung.
Originally Posted by
RChung
For two tires A and B, if Crr(A) > Crr(B) on drums then *almost always* Crr(A) > Crr(B) on the road (below the impedance breakpoint).
Yes, and this also holds for the two sets of data I referenced. But, at recommended pressures the rollingresistance.com site has the 32c tires as 7% worse than the 25c (11.4 vs 10.7 watts) whereas eyeballing the FLO data it looks like it is ~7% in the opposite direction so a 14% discrepancy between the two data sets (note the recommended pressures from the rolling resistance site are 100psi for the 25s which in fact is just into the impedance breakpoint, if we did 95psi instead it would be before it; it is 75psi for the 32c). So, even below the breakpoint there is a discrepancy. There still are impedance effects below the breakpoint, that is just the point where impedance dominates. So maybe that is why the drum and road data are not agreeing here.