Rob, here are a couple:
(tire diameter in inches) x 3.1415(pi) x (RPM) x 60(minutes in an
hour) / (final drive ratio e.g. 3.7) / 63360 (inches in a mile) = MPH
or
(tire circumference in inches) x (RPM) x 60(minutes in an hour) / (final
drive ratio e.g. 3.7) / 63360 (inches in a mile) = MPH
Examples using Hoosier Vintage TD 5.50 / 15 which has a stated diameter of
24.7 inches, 5800 RPM at end of straight, 3.7 final drive (assuming 4th is 1:1)
24.7 x 3.1415 x 5800 x 60 / 3.7 / 63360 = 115.1851 mph
or using a measured tire circumference of 77.5 inches, the rest the same...
77.5 x 5800 x 60 / 3.7 / 63360 = 115.044 mph
- Tony Drews
Here are the conversions that are combined into the formulas
engine RPM / final drive = wheel RPM
RPM x 60 = Rotations per Hour
one rotation = circumference worth of movement
1 mile = 63360 inches
diameter x pi (approx. 3.1415) = circumference
At 05:52 PM 7/13/2005, rob wrote:
>Does any one have the fromula handy that will calcuate mph?
>Useing engine rpm ,final drive R/O, tire size etc . thanks
>
> rob
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