Quote:
Originally Posted by MetroMPG
Really?
The fancy drag & rolling resistance formulas disagree by a pretty wide margin.
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How so? The Cd of a bunny is .45 with around 20ft^2 of reference area IIRC. Weight is ~2300lbs with a driver, and the middle of the Crr range is ~.01 (.006 for LRRs to .015 for snow tires).
This calc gives 17+hp at 60mph and 21+hp at 65mph. Since that's at the wheels, we still have losses from the trans/CVs. Assuming the driveline is ~90-95% efficient, then the engine will need to make ~18-20hp@61mph.
Course, in terms of engine efficiency, there isn't much to be gained by an increase in load thanks to hills for example, going from ~220g/kWh to ~200g/kWh, but on the way down BSFC would drop into the ~300g/kWh area, so that's gonna hit mileage unless they have mostly flat driving or P&G on the way down.