Gear Ratio

This Gear Ratio calculator computes the rear end gear ratio, or axle ratio, or how many times the driveshaft spins for one full rotation of the tires. 

INSTRUCTIONS: Choose units and enter the following:

• (d) Number of Driveshaft Rotations
• (t) Number of Tire Rotations

Gear Ratio: The value is returned as a ratio (ex: 3.73:1)

The Math / Science

Calculating the rear end gear ratio, or axle ratio, is a straightforward process that involves knowing the number of revolutions of the driveshaft compared to the number of revolutions of the rear wheels. Here's a step-by-step method to determine it:

1.  Jack Up the Vehicle: Ensure the vehicle is safely lifted and securely supported, so the rear wheels can rotate freely.
2.  Mark the Driveshaft and Tire: Mark a reference point on the driveshaft and a corresponding mark on the rear tire. You can use chalk or a piece of tape for this.
3.  ** Rotate the Driveshaft**: Rotate the driveshaft by hand (or have someone rotate it) while counting the number of complete revolutions. Keep in mind, you may need to rotate it several times to get an accurate count.
4.  ** Count the Tire Revolutions**:  Count how many times the rear tire rotates for each complete revolution of the driveshaft.
5.  Calculate the Gear Ratio:

Use the following formula:

Gear Ratio=Number of Driveshaft RevolutionsNumber of Tire Revolutions\text{Gear Ratio} = \frac{\text{Number of Driveshaft Revolutions}}{\text{Number of Tire Revolutions}}Gear Ratio=Number of Tire RevolutionsNumber of Driveshaft Revolutions​

For example, if the driveshaft makes 4.11 revolutions for every 1 revolution of the tire, then the gear ratio is 4.11:1.

Example Calculation

Rotate the driveshaft 4.11 times.

The rear wheel makes 1 complete revolution.

Thus, the rear end gear ratio is 4.11:1.

Note:

Ensure the vehicle is safely secured and follow all safety procedures.

Accurate measurement is crucial; consider using a helper or a more precise method if necessary.

If you're measuring this to verify a specific gear ratio or to adjust it for performance reasons, you may also check your vehicle’s specifications or use a gear ratio calculator if you have the number of teeth on the ring and pinion gears.