Gear Ratio Calculator

Calculate gear ratios, find optimal transmission setups, and determine speed-to-RPM relationships. Perfect for automotive tuning and performance optimization.

Calculate Gear Ratios

Input gear (motor/engine side)

Output gear (wheel/load side)

Quick Reference

Gear Ratio Formula:
Driven Teeth ÷ Driving Teeth
Speed Formula:
RPM × Circumference ÷ Gear Ratio
Common Ratios:
• 1st: 2.5-4.0:1
• 5th/6th: 0.6-0.9:1
• Final: 2.5-4.5:1

Performance Tips

Lower ratios = more acceleration, less top speed
Higher ratios = higher top speed, less acceleration
Overdrive gears (0.5-0.9:1) improve fuel economy
Close ratio gears keep engine in power band

Common Applications

Racing
Close ratios, higher final drive
Street
Balanced ratios, overdrive top gear
Economy
Tall gears, deep overdrive
Off-Road
Low ratios, high torque multiplication

Understanding Gear Ratios

How Gear Ratios Work

Gear ratios determine the relationship between input and output speed and torque. A 3:1 ratio means the driving gear must turn 3 times for the driven gear to turn once. This trades speed for torque - you get 3 times the torque but 1/3 the speed.

In automotive applications, multiple gear ratios in the transmission work with the final drive ratio to provide the optimal balance of acceleration and top speed for different driving conditions.

Practical Applications

  • • Choose gear ratios based on engine power band and intended use
  • • Lower numerical ratios provide better acceleration from a stop
  • • Higher numerical ratios allow for higher top speeds
  • • Overdrive ratios (less than 1:1) improve fuel economy at cruise
  • • Close-ratio transmissions keep the engine in its optimal RPM range

Optimization Tips

Track Racing

Use close ratios and match top gear to track's longest straight. Aim for peak power at the end of straights.

Street Performance

Balance acceleration and cruising ability. Keep highway RPM between 2000-2500 for best efficiency.

Fuel Economy

Use tall gears and deep overdrive. Target 1500-2000 RPM at cruise speeds for maximum efficiency.

Drag Racing

Optimize for peak power through each gear. Calculate to hit rev limiter just past the finish line.