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Old 12-09-2008, 03:32 PM   #6 (permalink)
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bearings and such

Originally Posted by MetroMPG View Post
Thought of another flaw in the calculator: CRR entered is supposed to be for the tires' resistance, but rolling resistance involves some drivetrain resistance as well (bearings, possible brake drag, CV/U joints, differential).

Determining your actual Crr experimentally and entering it would be best. See:

Darin,the SAE considers bearing losses to be so low,they are basically ignored with respect to RR.-------------------------------

Power-train efficiency is a consideration,once road-load power is determined,to calculate engine power required to overcome loads.-----------------------

I've been using 95 % efficiency for manual-transmission vehicles,as this is a value ascertained by the SAE in early research on pickups and big trucks.Basically,once you've arrived at aero and RR horsepower necessary at the drive wheels,you divide that value by 0.95,and it spits-out Bhp at the flywheel.Multiplying that value by BSFC yields pounds of fuel,and dividing that figure by 6.1626 pounds/gallon( for gasoline ),it spits out gallons,then divided by distance for mpg.Sorry for the US Standards!--------------

Sorry,I do not have any data for automatic transmission vehicles.-----------------------

Thanks for creating the calculation tool as I'm sure it will pay dividends to anyone who uses it. Way cool!!!!!!!!!!!
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