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Aerodynamics Seminar # 7 - by Phil Knox
This post was originally written by Phil Knox (aerohead), and it first appeared on the MaxMPG group. Phil has done a lot of work educating the masses about the critical role aerodynamics play in efficiency, and has spurred many in the DIY crowd to take matters into their own hands.
This is the seventh in a series which I'm reproducing here with permission.
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Here's a formula that will allow you to estimate the horsepower necessary at the drivewheel to overcome your tires rolling resistance (power absorption).
The formula is for radial tires only,and is for 70-degrees F,smooth road,dry road, proper inflation pressure.
Horsepower HP= V/375 times[0.01184 W + 0.000353(V-66) W].
Velocity V is in miles per hour, Weight W is in pounds.
If your speed is below 66-mph,then the second term within the parenthesis falls out.
Again,to get flywheel power,take your result and divide by 0.95. This yields Bhp the engine or electric motor must provide to the powertrain,at 95% mechanical efficiency for the powertrain.
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