Speedometer Error Table: Actual speed by Original tyre diameter
Reference table of actual speed for Speedometer Error across a range of original tyre diameter values — exact, engine-computed figures you can read off at a glance.
Speedometer Error Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Actual speed
102.85
- Speedometer error
- 2.85%
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Speedometer Error Calculator
The Speedometer Error Calculator works out your actual speed, along with 1 related figure in an instant. Enter original tyre diameter, new tyre diameter and indicated speed and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the original tyre diameter.
- Enter the new tyre diameter.
- Enter the indicated speed.
- Read off your actual speed, together with speedometer error — the calculator updates automatically, with no button to press.
Formula
The Speedometer Error Calculator uses the formula:
Actual speed = Indicated speed × New tyre diameter ÷ Original tyre diameter
Worked example
For example, with original tyre diameter of 632 mm, new tyre diameter of 650 mm and indicated speed of 100 km/h, the actual speed is 102.85.
| Original tyre diameter | 632 mm |
|---|---|
| New tyre diameter | 650 mm |
| Indicated speed | 100 km/h |
| Actual speed | 102.85 |
|---|---|
| Speedometer error | 2.85% |
Results are estimates for educational use, not professional advice.
Key terms explained
- Diameter
- The distance across a circle through its centre — twice the radius.
Frequently asked questions
A larger tyre travels further per turn, so you actually go faster than the speedometer shows, and the odometer under-counts.
Multiply the indicated speed by the ratio of new to old tyre diameter. Bigger tyres raise the true speed.
A few percent is common and usually legal, but large changes can cause speeding tickets and odometer errors.
Use the tyre's specification or measure the overall diameter. Both tyres must be entered in the same units.
The Speedometer Error Calculator uses the formula: Actual speed = Indicated speed × New tyre diameter ÷ Original tyre diameter. For example, with original tyre diameter of 632 mm, new tyre diameter of 650 mm and indicated speed of 100 km/h, the actual speed is 102.85.
Enter the original tyre diameter. Enter the new tyre diameter. Enter the indicated speed. Read off your actual speed, together with speedometer error — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Speedometer Error: Formula, Steps & Examples
Learn how to calculate Speedometer Error — the formula explained step by step, with worked examples and a free calculator to check your answer.