Gearing Formulas

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Gear Ratio means 'Overall Gear Ratio', in the gear you want to calculate,
that includes the Primary drive gear ratio on a motorcycle gearbox.

To figure miles per hour, multiply the engine RPM by the Wheel Diameter in inches and divide this by the Gear Ratio times 336

MPH =	RPM x wheel diameter (in inches)	or:	2,275 x 26.5	= 59.81 MPH

	gear ratio X 336		3.0 x 336

To figure tire diameter of Radial tires, multiply the Section Width by 2. Multiply that by the Aspect Ratio. Divide that by 24.5 and add the wheel diameter

TD =	(section width x 2) x (aspect ratio x .01)	+	wheel diameter	=	tire diameter

	24.5

or:

TD =	(235 x 2) x .60	+	15	=	26.5"

	24.5

To figure engine speed (RPM), multiply by the Speed in MPH, by the rear axle gear ratio times 336. Divide this by the tire diameter in inches.

RPM =	MPH x gear ratio x 336	or:	60 x 3.0 x 336	= 2,282 RPM

	tire diameter		26.5

To figure tire diameter, multiply the speed in MPH by the rear axle ratio. Divide that by the RPM and multiply the result by 336

TD =	MPH x gear ratio	x	336	=	tire diameter

	RPM

or:

TD =	60 x 3.0	x	336	=	26.5 inches

	2,275

To figure the rear axle ratio, multiply the engine speed in RPM by tire diameter. Divide this by speed in MPH and divide that by 336.

Gear Ratio =	RPM x tire diameter	divide by:	336	=	ratio

	MPH

or:

Gear Ratio =	2,275 x 26.5	divide by:	336	=	2.99:1

	60

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