Math & Business Productivity

Gear Ratio Speed Calculator

Calculate vehicle speeds in MPH based on engine RPM, tire diameter, transmission gear ratio, and rear axle ratio.

Interactive Calculator

1. Provide Details

Engine RPM

RPM

Tire Diameter (inches)

Transmission Gear Ratio

Rear Axle / Differential Ratio

2. Output Results

Overall Gearing Ratio3.73 :1

Vehicle Speed (MPH)64.6 MPH

Vehicle Speed (km/h)104.0 km/h

How to Calculate: Formula & Steps

Computes ground speed by determining wheel RPM and multiplying by tire circumference.

Formula Used:Speed (MPH) = (RPM × Tire Diameter) ÷ (Transmission Ratio × Axle Ratio × 336)

Step-by-Step Calculation Example

At 3,000 RPM with 26" tires, 1.0 transmission gear, and 3.73 axle, the speed is 62.2 MPH.

Inputs and Assumptions

Enter values that match your project or situation. The calculator uses the following fields and defaults; update them before relying on the estimate.

Engine RPM: Default: 3000 RPM
Tire Diameter (inches): Default: 27 in
Transmission Gear Ratio: Default: 1 :1
Rear Axle / Differential Ratio: Default: 3.73 :1

Common Mistakes to Avoid

Confusing tire radius with tire diameter in inputs.

Practical Use Cases

Drivetrain gearing optimizations
Transmission speed checking

Expert Tips

A lower gear ratio increases acceleration, while a higher ratio improves highway fuel efficiency.

Disclaimer

This calculation tool is provided for educational and informational estimation purposes only. Results are based on mathematical formulas and user-supplied parameters. They do not constitute formal underwriting, financial, tax, engineering, or legal determinations.