How to Calculate the Gear Ratio for a Tire
You can calculate the gear ratio for a tire manually or by utilizing an online calculator. Gear ratio is related to the size of the tire and the RPM output of the engine. When you decrease the size or diameter of the tires on your vehicle, the engine speed will increase. This increase will change the gear ratio.
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Instructions
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Manual
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1
Count the number of pinion gear teeth and ring gear teeth when installing a new gear set in your vehicle. The pinion is connected to the vehicle's driveshaft and turns the ring gear. The ring gear in connected to the axle and sits at a 90-degree angle to the pinion gear.
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2
Divide the ring gear teeth by the pinion teeth gear. The result is gear ratio.
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3
Measure the diameter of one of the tires on your vehicle with a tape measure.
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4
Calculate gear ratio by using the equation “rpm * tire diameter/mph * 336.” RPM and mph is the average speed of the vehicle when traveling on the road.
Online
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5
Go to an online gear ratio calculator. There is a link in the Resources section.
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Enter the diameter of the tires in the Original Tire Diameter field.
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7
Enter the diameter of a new set of tires in the New Tire Diameter field.
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Enter the current gear ratio for the vehicle.
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Click the “Compute” button to see the gear ratio for the new tires.
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1
Tips & Warnings
The diameter of the tire is measured from the outer edge of the tire, not from the inside of the wheel wall.
