## Speedometer Gear Calculator

**Recommended Driven Gear Teeth:**

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## How to Calculate Speedometer Gear Teeth

When changing the size of wheels and tires on a vehicle, it is often necessary to recalibrate the speedometer to ensure accurate readings. For a manual speedometer, this involves replacing the driven gear. The number of teeth required for the driven gear depends on factors such as tire size, axle ratio, and the number of teeth on the drive gear in the speedometer. To calculate the number of teeth needed for the driven gear, follow the formulas below:

### 1. Calculate the revolutions per mile for the wheel:

rev/mile = 20,168 / tire diameter(alert-success)

Use a tire size calculator or try our tire size calculator to determine the tire diameter.

### 2. Calculate the number of teeth for the driven gear:

driven teeth = (drive teeth × axle ratio × rev/mile) / 1,001(alert-success)

The number of driven teeth is obtained by multiplying the number of drive teeth by the axle ratio and the tire revolutions per mile, then dividing the result by 1,001.

Using these formulas, you can calculate the appropriate number of teeth needed for the driven gear to recalibrate the speedometer. Additionally, you may find our tire comparison calculator useful for comparing different tire sizes.