Tool
Motorcycle Speed in Gear Calculator
The calculator estimates road speed from engine RPM, the primary ratio, each gearbox ratio you enter, the sprockets, and the rear tire. MPH equals RPM × wheel circumference in miles × 60 ÷ overall reduction.
Model at the RPM you entered
Overall reduction is primary × gearbox × (rear ÷ front). MPH is an estimate, not a GPS reading.
| Gear | Gearbox | Overall | Speed |
|---|
When to use this calculator
Use it when you want a speed table before you change sprockets, or when you want to see how tall sixth gear is at a cruise RPM. You enter the gearbox yourself. The page does not guess a model-year transmission.
The tire can come from a size stamp or from a tape around the loaded tire. A size-based circumference is an unloaded geometric estimate. A measured circumference is better if you already have the tape figure.
Primary ratio is not the same as first gear. If you omit primary, or set it to 1 when the motorcycle is not 1:1, every MPH figure will be wrong by that factor.
Empty gears are skipped. Zero teeth or zero RPM produce a field error instead of Infinity.
Worked speeds
With the default primary, gearbox, and 180/55-17 tire, sixth gear is the tallest row in the table. Change the rear sprocket and watch that row move.
One fewer front tooth raises overall reduction and lowers MPH in every gear. Does that trade match the roads you actually ride?
If you enter 80 inches instead of the 180/55-17 estimate, the table uses 80 ÷ 63,360 miles per revolution. That is the clean way to test the formula against a tape.
Technical questions
What is overall reduction in the formula?
Overall reduction is primary × gearbox ratio × (rear teeth ÷ front teeth). Wheel revolutions per minute are engine RPM divided by that product. Miles per hour are then wheel RPM × circumference in miles × 60.
How is 180/55-17 turned into circumference?
Sidewall height is 180 × 0.55 = 99 mm. Diameter is 17 × 25.4 + 2 × 99 = 629.8 mm. Circumference is π × 629.8 mm. That figure becomes miles for the speed equation.
Why does the table disagree with my GPS?
The model assumes the tire rolls without slip at the geometric circumference. A GPS reading includes lean, wear, pressure, and any speedometer offset. Treat the table as a comparison tool.