Gear Ratio & Speed Calculator
Calculate vehicle speed from gear ratios, RPM, and tire size. Enter values for instant results with step-by-step formulas.
Frequently Asked Questions
How do I find my gear ratios?
Check your car's owner manual or search online for '[Car Model] transmission ratios'. Common codes: T56, 4L60E, ZF8.
How does tire size affect speed?
Larger tires cover more ground per rotation. They increase top speed (theoretically) but decrease acceleration.
What is a 1:1 gear?
Usually 4th or 5th gear. Input shaft speed equals Output shaft speed. Most efficient gear (no reduction loss).
Why do dynos use 1:1 gear?
To get the most accurate horsepower reading by minimizing transmission friction losses.
What is 'Crawling Ratio'?
Used in off-roading. First Gear × Low Range × Axle Ratio. Can be 100:1 or more.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.