How to compare tyre sizes
- Type the Current tyre size from its sidewall, such as 225/45R17. Off-road sizes like 33x12.50R15 work too.
- Type the New tyre size you’re considering.
- Read the difference in overall diameter, the side-by-side comparison and what your speedometer will show with the new tyres.
Common 17 to 19 inch sizes
| Size | Overall diameter | Revs per mile |
|---|---|---|
| 205/55R16 | 631.9 mm | 810.7 |
| 225/45R17 | 634.3 mm | 807.6 |
| 225/40R18 | 637.2 mm | 803.9 |
| 235/40R18 | 645.2 mm | 794.0 |
| 245/35R19 | 654.1 mm | 783.2 |
Plus sizing
Fitting a larger wheel with a lower-profile tyre, such as moving from 205/55R16 to 225/45R17, is called plus sizing. Done well, the overall diameter stays almost the same (here 0.38% larger), so the speedometer and gearing barely change, while the shorter sidewall sharpens the steering. The trade-off is usually a firmer ride and wheels that are easier to damage on potholes. A wider tyre can also rub on suspension parts or arches, so check clearance before buying.