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As for the formula for figuring out RPM's, I think it is circumfrence divided into 5280.
I cheated by using the chart the state of WA uses in the "SPECIFICATIONS FOR SCHOOL BUSES".
It is so much easier using someone else's work. <G>
Mark O.
To use the formula above for revolutions (by the tire) per mile, the tire diameter needs to be expressed in feet, or alternatively, the 5280 (ft/mile) value could be converted to inches.
The following is a formula I use for relating rpm (motor revs per minute, not tire revs per mile) to mph, final drive gearing, transmission gearing and tire diameter.
rpm = (mph X rearend ratio X trans. ratio) / (tire dia. X .002975)
Notes 1. trans. ratio in high gear is generally 1:1 (trans. ratio =1 )unless the transmission is an overdrive 2. The actual rpm in an automatic transmission vehicle will usually be higher than the formula will calculate due to torque converter slippage. The formula is still usefull for approximating rpm differences due to changes in tire diameter and gearing. |
email Will B.
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