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The formula:
MPH = RPM X LRTR / GR X 168
Where:
MPH = obvious
RPM = Engine RPM
LRTR = Loaded Rear Tire Radius. Axle center to pavement.
GR = Overall gear ration. Trans ratio X Rear end.
168 = Fudge factor. Handles conversion of revs per MINUTE to miles per HOUR, radius in INCHES to MILES per hour.
Some people use a bogus variation on this formula: Rear Tire diameter, fudge factor 336. Wrongo - portion of tire above the ground does not affect speed, this formula does not take loading into account. |
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