Tyre size comparison
Compare two tyre sizes.
Diameter change
+1.6%
Speedo reads 100 km/h, you’re doing
101.6
Within the usual ±3% rule of thumb, so ABS, stability control and the speedometer should cope. Check clearance to the guards and suspension at full lock and full compression, and that the new width suits your rim. With a bigger tyre your speedo under-reads: you're travelling faster than it shows.
| Current | New | Change | |
|---|---|---|---|
| Diameter | 637 | 647 | +10 |
| Sidewall | 90 | 82 | -8 |
| Width | 225 | 235 | +10 |
| Revs/km | 500 | 492 | -8 |
Current, with the new size dashed
Tyre size comparison questions
Will bigger tyres affect my speedometer?
Yes, if the overall diameter changes. A tyre 3% taller means you travel about 3% faster than the speedometer shows. Keep the change within about 3%, and check your state's rules on modified wheel and tyre sizes.
What is plus sizing?
Fitting a larger rim with a lower-profile tyre so the overall diameter stays about the same, for example 225/45 R17 to 225/40 R18. Steering gets sharper; ride gets firmer and the rims are easier to damage on potholes.
Can I fit a different tyre size to my car?
Usually only sizes listed on your tyre placard, or ones within the limits your state allows for modified vehicles. The load index and speed rating must still match or beat the placard. Ask a tyre fitter, and check with your insurer.