Choose a method and enter values
Example data table
Use these samples to sanity-check your inputs and units.
| Method | Inputs | Slip | Expected speed |
|---|---|---|---|
| Distance & time | Distance: 12 km, Time: 0.2 h | — | ≈ 60 km/h |
| Wheel rpm & tire | Wheel: 900 rpm, Diameter: 26 in | 2% | ≈ 107 km/h |
| Engine rpm & gearing | Engine: 3000 rpm, Gear: 1.82, Final: 3.73, Tire: 26 in | 0% | ≈ 83 km/h |
Formulas used
- Distance method: speed = distance ÷ time.
- Wheel rpm method: v = (RPM × π × D) ÷ 60.
- Gearing method: wheelRPM = engineRPM ÷ (gear × final × transfer).
- Slip correction: veffective = videal × (1 − slip/100).
- Unit conversions: km/h = m/s × 3.6, mph = m/s × 2.23694.
How to use this calculator
- Select a method that matches your available measurements.
- Enter values and choose the correct units for each field.
- Optionally set slip and enable breakdown for extra details.
- Press Submit to view the result above the form.
- Use the export buttons to download CSV or PDF.
FAQs
1) Which method should I choose?
Use distance and time for road tests. Use wheel rpm when you have sensor data. Use engine rpm and ratios when estimating speed from drivetrain specs.
2) Why does tire diameter affect speed so much?
Speed depends on rolling circumference. A small diameter change multiplies across every wheel revolution, so the effect becomes large at high rpm.
3) What does slip mean here?
Slip models loss between ideal rolling speed and real travel speed. It can represent tire slip on low traction, or small effective-radius errors from tire deformation.
4) Can I compute speed for multiple gears?
Yes. In the gearing method, paste gear ratios separated by commas or spaces. The tool builds a gear speed table at your entered engine rpm.
5) Why is my calculated speed higher than GPS?
Common causes are optimistic tire diameter, ignoring slip, or using indicated rpm values that differ from true rpm. Try enabling breakdown and adjusting slip slightly.
6) How do I get more accurate tire diameter?
Use the loaded rolling radius from manufacturer data when available. Otherwise, measure rolling circumference by marking the tire and counting one full revolution under load.
7) Does gear efficiency change speed?
Efficiency mainly affects torque and power delivered, not kinematic speed. Speed is set by rotation ratios and tire circumference; slip is the practical correction factor.
8) Is this suitable for engineering reports?
For quick checks, yes. Export the CSV or PDF for documentation, and note assumptions like rolling radius, slip, and measurement uncertainty.