Speedometer gear calculator

Calculate the appropriate speedometer gear ratio based on your vehicle's specifications

Input Parameters

Calculation Results

Required Speedometer Gear Ratio

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Calculation Formula

Gear Ratio = (Wheel Circumference × Odometer Speed) / (Tire Circumference × 63360 × Cluster Ratio × Final Drive Ratio)

Where:
Wheel Circumference: Distance traveled in one revolution of the wheel (in inches)
Odometer Speed: The desired reading on the speedometer at 60 mph
Tire Circumference: Distance traveled in one revolution of the tire (in inches)
Cluster Ratio: Transmission gear ratio
Final Drive Ratio: Rear axle ratio
63360: Number of inches in a mile

Notes

The calculated gear ratio is for the speedometer gear that will mount to your speedometer cable. Ensure you select a gear that matches your speedometer's available range. For most applications, a 0.300" to 0.400" speedometer gear is standard.

Speedometer gear calculator Calculator Usage Guide

Learn how to use the Speedometer gear calculator and its working principles

How to use the calculator

  1. Enter your vehicle's wheel diameter in inches
  2. Enter your tire's circumference in inches
  3. Enter the recommended odometer speed at 60 mph (e.g., 60 mph is the standard value)
  4. Enter your transmission cluster ratio (e.g., 3.55)
  5. Enter your final drive ratio (e.g., 4.10)
  6. Click the "Calculate" button to determine the required speedometer gear ratio

Understanding the results

The calculator provides the speedometer gear ratio needed for your vehicle. This ratio ensures that your speedometer reads accurately at highway speeds. The formula used is based on the relationship between wheel rotation, tire size, transmission ratio, and the speedometer's reading.

Example Calculation

If you have a vehicle with a 30-inch diameter wheel, 30.5-inch circumference tire, and uses a 3.55:1 transmission ratio with a 4.10:1 final drive ratio, you would enter these values and click "Calculate" to determine the correct speedometer gear.

Important Notes

  • Always use accurate measurements for your wheel diameter and tire circumference
  • The recommended odometer speed at 60 mph is typically 60 mph, but some manufacturers may specify a different value
  • Once installed, speedometer gear ratios cannot be easily adjusted, so ensure your calculation is accurate
  • If you're replacing a speedometer gear, note that different speedometers may use different gear sizes