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'mechanical friction'
I'm throwing a caution flag on this play.
'Mechanical' friction would have to do with tribology ( hydrodynamic, viscous shearing forces associated with any lubricated, rotating or sliding components).
An engine's internal friction associated with pumping losses is a function of the square of the rpm. If an aero-modded road vehicle is evaluated at a given, constant test velocity ( fixed rpm ), once thermally equilibrated at the same ambient outdoor temperature as 'pre-modification' benchmarks were obtained, there'd be no change.
Same for transmission/transaxle, u-joints, differential, C-V joints, wheel bearings.
Brake-shoe and brake-pad drag would be presumed as a constant.
The mechanical efficiency of an automobiles powertrain is a constant percentage, although varies as a function of transmitted power.
As aero drag is reduced, Road Load falls, placing the engine under a lower load, and if proper gear-matching is not performed, the engine's BSFC will fall to a higher consumption 'island' on it's map, and we can lose up to 30% of some streamlining benefit, indicating 'less' of a drag reduction, if relying on some delta-mpg metric as an indirect measure of delta-CdA.
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Last edited by aerohead; 12-14-2023 at 11:03 AM..
Reason: typo
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