Free · Physics models
Ideal Gear and Tire Road Speed
Estimate road speed from engine revolutions, tire diameter and the transmission and final-drive ratios.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
A 600 mm tire at 3,000 engine RPM with a 1:1 gear and 3:1 final drive gives about 113.10 km/h.
Speed = engine RPM × tire circumference / (gear ratio × final-drive ratio), with time and length converted.
Worked example
Enter these known values and leave the other values blank.
- Tire diameter
- 600 mm
- Engine RPM
- 3000 rpm
- Transmission gear ratio
- 1
- Differential gear ratio
- 3
- Speed
- 113.1 km/h
Assumptions and limitations
- Tire diameter is the effective rolling diameter; slip, deformation and converter losses are omitted.
- Ratios divide engine speed to obtain wheel speed. The retained domain uses positive values and engine speed below 30,000 RPM.
- The circumference calculation retains π ≈ 3.14159265359 from the captured model; results are estimates rather than measured road speeds.
- Enter known quantities and leave the unknown blank. Editable quantities support inverse solutions and locks; inconsistent locked quantities are reported. Unit selectors convert the quantity independently of its display.
Common questions
Which tire diameter should I enter?
Use effective rolling diameter. A nominal unloaded tire dimension can differ from the diameter that describes actual distance per wheel turn.
What does a larger final-drive ratio do?
At the same engine RPM and tire diameter, it reduces wheel RPM and ideal road speed.
How do I use the inverse calculation?
Clear the quantity you want to find and enter the remaining known values in their selected units. The model can only solve branches with enough independent information.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.