How to use this calculator
- Enter RPM and tire diameter. Use the shift RPM, rev limit or cruise RPM and the loaded tire diameter.
- Enter drivetrain ratios. Enter final drive, transfer ratio and each transmission gear ratio.
- Read speeds by gear. Compare the road speed in each gear at the same target RPM.
- Use adjacent checks. Use RPM drop, final drive and converter slip calculators to refine the setup.
How it works
Each gear starts with its overall ratio:
overall = gear_ratio x final_drive x transfer_ratio
Wheel speed is engine speed divided by that ratio:
wheel_rpm = engine_rpm / overall
Road speed follows from tire circumference:
speed = wheel_rpm x pi x tire_diameter / 60
Worked example
Verified against the live calculator
At 6500 rpm with a 26 in tire, 3.73 final
drive and 3.50 / 2.10 / 1.45 / 1.00 / 0.80 / 0.63 gears, first
overall ratio is 13.055 and sixth overall ratio is 2.35.
The calculator reports the speed in every gear at the same target RPM so the spread
is visible before changing final drive or tire size.
Frequently asked questions
How do you calculate speed in each gear?
Multiply the transmission gear ratio by final drive and transfer ratio to get overall ratio. Wheel RPM is engine RPM divided by overall ratio, and road speed is wheel RPM times tire circumference.
Should I use measured tire diameter?
Use loaded or measured tire diameter for the best match to real road speed. Catalog diameter and tire-size math can differ from the rolling diameter under load.
Does this include converter or clutch slip?
No. It is a mechanical ratio table. Torque-converter slip, clutch slip, tire growth and rev-limiter tolerance can move measured speed away from the table.
How does this differ from the vehicle speed calculator?
The vehicle speed calculator solves one gear at a time. This page calculates a six-gear table at the same target RPM so gear spacing is easier to compare.
Method & assumptions
- Mechanical ratio math only: no torque-converter slip, clutch slip, tire growth or wheelspin.
- Use loaded tire diameter for real-road agreement; use tire-size math only for early comparisons.
- For one-gear speed checks use the vehicle speed calculator. For cruise RPM use the engine RPM calculator.
- Use RPM drop, final drive ratio and converter slip for adjacent drivetrain checks.