Vehicle Gear Ratio Calculator
Speed from RPM
Calculate vehicle speed from engine RPM and gearing
RPM from Speed
Calculate engine RPM from vehicle speed and gearing
Formula
Speed (mph) = (RPM x Tire Diameter) / (Gear Ratio x Final Drive x 336); RPM = (Speed x Gear x Final x 336) / Tire Diameter
Frequently Asked Questions
What is a final drive ratio?
The final drive ratio (also called axle ratio or differential ratio) is the last gear reduction between the transmission and the wheels. A higher number (e.g., 4.10) provides more acceleration but lower top speed and higher RPM at highway speeds. A lower number (e.g., 3.08) provides better highway fuel economy but slower acceleration.
How do I find my tire diameter?
Tire diameter can be calculated from the tire size. For example, 265/70R17: width is 265mm, aspect ratio is 70%, rim is 17 inches. Sidewall height = 265 x 0.70 = 185.5mm = 7.3 inches. Diameter = (7.3 x 2) + 17 = 31.6 inches. Many online tools can calculate this from your tire size.
What gear ratio is best for towing?
Higher numerical ratios like 3.73 or 4.10 are better for towing because they provide more torque multiplication. This makes pulling heavy loads easier, especially from a stop and on hills. The trade-off is lower highway fuel economy.
You may also need
A
0-60 Acceleration Time Calculator
Free 0-60 acceleration time calculator. Estimate a vehicle's acceleration time based on horsepower, weight, drivetrain, and conditions.
Science~
Wheel Offset Calculator
Free wheel offset calculator. Compare wheel and tire fitment, calculate offset differences, and check if new wheels will fit your vehicle.
EverydayA
Motorcycle Gear Ratio Calculator
Free motorcycle gear ratio calculator. Calculate sprocket ratios, top speed, and RPM for different front and rear sprocket combinations.
Science