Gear Ratio Calculator

Calculate gear ratios, speed ratios, and torque ratios for simple and compound gear trains.

Inputs

Gear Type

Input Speed (RPM)

Input Torque (N·m)

Stage 1 Gears

Driving Gear Teeth

Driven Gear Teeth

Efficiency (%)

About Gear Ratios

Calculate gear ratios, speed ratios, and torque ratios for simple and compound gear trains.

Common Applications

Calculate transmission gear ratios and vehicle speed
Design gear trains for mechanical systems
Analyze torque multiplication in gearboxes

Results

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How Gear Ratio Calculation Works

Overall Ratio = Transmission Ratio × Final Drive Ratio | Speed = (RPM × Tire Diameter) / (Overall Ratio × 336)

Gear ratios determine the mechanical advantage between engine RPM and wheel speed. Lower numerical ratios provide higher top speeds, while higher numerical ratios provide more torque multiplication for acceleration. This calculator helps optimize gearing for performance or efficiency.

1
Enter Transmission Ratios
Input the gear ratio for each transmission gear
2
Enter Final Drive Ratio
Provide the differential or final drive ratio
3
Enter Tire Size
Input tire diameter to calculate actual road speed
4
View Speed Chart
See calculated speeds at various RPM points for each gear

Use Cases

Performance Optimization

Optimize gear ratios for drag racing, autocross, or track performance

Final Drive Selection

Choose the right ring and pinion ratio for your driving needs

Tire Size Impact

Calculate how changing tire size affects effective gearing and speedometer accuracy

RPM Planning

Determine what RPM you will be at for cruising speeds or at the end of a quarter mile

Tips

1
Shorter gears (higher numerical ratio) improve acceleration but reduce top speed and fuel economy
2
Taller gears (lower numerical ratio) improve highway fuel economy and reduce engine wear
3
Consider where your engine makes peak power when selecting final drive ratios
4
Tire size changes effectively change your gear ratio - larger tires act like taller gearing
5
Calculate RPM at highway speeds to ensure engine stays in efficient operating range

Common Mistakes

Confusing 'shorter' and 'taller' gearing terminology with numerical values
Not accounting for tire size when calculating speed from RPM
Choosing gears based only on acceleration without considering highway RPM
Forgetting that changing final drive affects ALL gears proportionally

Frequently Asked Questions

What is the difference between transmission and final drive ratio?

Transmission ratio changes with each gear shift. Final drive ratio (differential) is constant and multiplies all transmission ratios. Overall ratio is transmission ratio times final drive ratio.

Should I get shorter or taller gears?

Shorter gears (higher number like 4.10) improve acceleration and towing but increase highway RPM. Taller gears (lower number like 3.23) improve fuel economy and reduce engine wear but slow acceleration.

How do tire size changes affect gearing?

Larger tires effectively create taller gearing (slower acceleration, lower RPM at speed). A 10% larger tire is like changing from 3.73 to 3.39 gears. Smaller tires do the opposite.

What RPM should I cruise at on the highway?

Most modern engines are efficient between 1,500-2,500 RPM. Higher RPM increases fuel consumption and wear. Calculate your cruise RPM when selecting final drive ratio.

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