225/45R17
Sidewall 101.25 mm and overall diameter about 634.3 mm (24.97 in).
Tire Size Calculator
Decode tire sizes like 225/45R17 and compare two sizes, with the speedometer difference.
km/h or mph
Result
Diameter change
+0.38%
- Actual speed when the speedometer shows 100
- 100.4
Tire dimensions
| Measurement | 205/55R16 | 225/45R17 |
|---|---|---|
| Sidewall height | 112.8 mm | 101.3 mm |
| Overall diameter | 631.9 mm (24.88 in) | 634.3 mm (24.97 in) |
| Circumference | 1,985 mm | 1,993 mm |
| Revolutions per km | 503.7 | 501.8 |
| Revolutions per mile | 810.7 | 807.6 |
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How the Tire Size Calculator works
A tire size like 225/45R17 means a tire 225 mm wide, with a sidewall 45% as tall as it is wide, on a 17-inch wheel. Enter a size to see the sidewall, overall diameter, circumference and revolutions per kilometre and mile; add a second size to compare them and see how much faster you really go when the speedometer shows a given speed.
Formulas
Diameter
diameter = wheel × 25.4 + 2 × (width × aspect ÷ 100)
Speedometer
actual speed = shown speed × new diameter ÷ old diameter
Examples
205/55R16 → 225/45R17
The new tire is 0.38% larger, so at an indicated 100 you're really doing about 100.4.
Frequently asked questions
How big a change is safe?
Most tire makers suggest staying within about 3% of the original diameter; always check load and speed ratings.
What does R mean?
Radial construction — almost all car tires today.
Why does the speedometer change?
It counts wheel turns; a larger tire travels further per turn.
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