Drivetrain

Gear Ratio Calculator

Calculate vehicle speed at any RPM based on tire size, axle ratio, and transmission gear. Perfect for gear selection and engine tuning.

Quick Presets

Results

Enter drivetrain specs to calculate speed and RPM

Common Gear Ratios

2.73-3.08 — Highway economy
3.21-3.55 — Balanced performance
3.73-4.10 — Towing/acceleration
4.30+ — Off-road/drag racing

How to Use

Enter your axle (differential) ratio
Enter the transmission gear ratio
Input total tire diameter
Set RPM to calculate speed

FAQs

What is a good highway RPM?

Most engines are efficient at 1800-2500 RPM at highway speed. Higher RPMs increase fuel consumption and wear.

Higher or lower axle ratio for towing?

Higher numerical ratios (like 4.10 vs 3.21) provide more torque multiplication, better for towing and acceleration but worse fuel economy.

Where do I find my axle ratio?

Check the door jamb sticker, owner's manual, or differential cover tag. You can also calculate it by counting driveshaft rotations per wheel rotation.

What's overdrive?

Overdrive gears have ratios less than 1.0 (like 0.75), meaning the output spins faster than the input. This reduces RPM at highway speeds for better fuel economy.

Limitations

Assumes no drivetrain losses
Does not account for tire slip
Transfer case ratio not included
Actual speed varies with conditions

Gear Ratio Calculator

Drivetrain Specs

Tire & Engine

Quick Presets

Results

RPM at Highway Speeds