Gear Speed Calculator
Road speed at a given engine speed in a chosen gear, plus the wheel speed and overall ratio.
Results
Speed
69.23
km/h
Speed
43.02
mph
Rotational speed
591.7
rpm
Ratio
5.0700
What this tool does
This is the calculation behind every gearing change: a shorter final drive lifts acceleration and costs top speed, a taller one does the reverse. Tyre circumference is easily measured — mark the tyre, roll the car one full turn and measure the ground between the marks.
Formula
v = rpm × circumference ÷ (ratio gearbox × final ratio)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
n | Rotational speed | rpm |
gr | Gear ratio | — |
fd | Final drive ratio | — |
tc | Tyre rolling circumference | m |
V | Speed | km/h |
VM | Speed | mph |
WR | Rotational speed | rpm |
TR | Ratio | — |
Worked example
- Rotational speed3000 rpm
- Gear ratio1.3
- Final drive ratio3.9
- Tyre rolling circumference1.95 m
- Speed69.23 km/h
- Speed43.02 mph
- Rotational speed591.7 rpm
- Ratio5.0700
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.