Quote:
Originally Posted by COcyclist
"it doesn't change, regardless of shape"- Speed??? between 20 and 250 mph
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1) the 'shape' determines Cd.
2) the Cd is constant within this velocity range ( this is 'low-speed, subsonic, incompressible-flow aerodynamics ).
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Caveat:
You may see some researches, say, for some Teslas, which were specifically tested for ventilation drag for the different OEM wheels offered, which DOES alter the Cd slightly, however, the difference barely makes it onto to the 'radar screen' in relation to overall drag.
Precise road testing would respect these dynamics in order to parse out actual changes from R-R or aero mods.