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:
- (DSR) Number of Driveshaft Rotations
- (WR) Number of Tire or Wheel 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:
- Jack Up the Vehicle: Ensure the vehicle is safely lifted and securely supported, so the rear wheels can rotate freely.
- 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.
- ** 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.
- ** Count the Tire Revolutions**: Count how many times the rear tire rotates for each complete revolution of the driveshaft.
- Calculate the Gear Ratio:
The Gear Raio formula is:
GR = DR/WR
where:
- GR = Gear Ratio
- DR = Number of Driveshaft Revolutions
- WR = Number of Tire or Wheel Revolutions
Example
For example, if the driveshaft makes 4.11 revolutions for every 1 revolution of the tire, then the gear ratio is 4.11:1. To find this, rotate the driveshaft 4.11 times and the rear wheel makes 1 complete revolution. Thus, the rear end gear ratio is 4.11:1.
Safty and Suggestion
Ensure the vehicle is safely secured and follow all safety procedures. If 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.
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