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I think that the difference in displacements is that the smooth drum test is essentially modelling a steady state contact patch at only one tire deflection, a deflection which is relatively small. On rough roads, the contact patch is constantly changing shape due to road surface so the tire is deflecting in various ways which range from less than to more than that seen on the drum.
However, the mechanism that gives tubulars higher RR on a smooth drum (hysteresis) is present both when the deflection is steady state vs. varying. Are you surmising that the somehow there is a difference in the hysteresis performance during changes in deformation amplitude?....and that it favors the tubular construction despite it having a structure with higher inherent losses (i.e. glue)?
I guess I'm trying to figure out how tubulars could have more RR at any given deflection amplitude at steady-state (just differences in wheel load or air pressure would cause this) yet they would somehow "magically" have less losses during the transitions between varying maximum amplitudes.
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On mildly rolling terrain, we really couldn't see any difference between the two taken as an average over time, but maybe the better RR of the clincher wheels was offsetting the weight penalty :-)
Exactly! Of course, data taken from a race isn't exactly "controlled", now is it?
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