Rim size chart
Rim size describes the wheel itself: its diameter, its width, and its offset. This chart covers diameter and the tyre sizes commonly fitted to each.
| Rim diameter | In mm | Common tyre sizes | Rolling diameter range | Examples |
|---|---|---|---|---|
| 15 in | 381 mm | 4 | 615–648 mm | 185/65R15, 195/65R15, 205/65R15 |
| 16 in | 406 mm | 6 | 621–664 mm | 195/55R16, 205/55R16, 215/55R16 |
| 17 in | 432 mm | 6 | 634–668 mm | 205/50R17, 215/55R17, 225/45R17 |
| 18 in | 457 mm | 6 | 636–669 mm | 225/40R18, 225/45R18, 235/40R18 |
| 19 in | 483 mm | 5 | 642–663 mm | 225/40R19, 235/35R19, 245/35R19 |
| 20 in | 508 mm | 3 | 673–687 mm | 245/35R20, 255/35R20, 275/30R20 |
The three numbers that describe a wheel
Diameter is the bead seat measurement in inches — the 16 in 205/55R16. It must match the tyre exactly; a 16-inch tyre will not go on a 17-inch rim.
Width is also in inches, measured between the bead seats, and is usually stamped as something like 7J. Unlike diameter, this has a range of acceptable tyre widths rather than one answer.
Offset, marked ET, is in millimetres and sets how far the mounting face sits from the wheel's centreline. It decides where the wheel sits in the arch. See wheel offset explained.
Going up a rim size
Fitting a larger rim usually means a lower-profile tyre to keep rolling diameter roughly the same — a plus-size. Keeping rolling diameter within about 1% keeps the speedometer accurate and the ABS and traction systems calibrated. Each of the tyre size comparisons shows the exact figure.
Related
How are these fitment figures calculated?
Fitment North calculates declared wheel and tyre geometry from the dimensions shown on the page, using the same tested method as the wheel-offset and tyre-size calculator. Tyre diameter uses rim diameter plus two calculated sidewalls; offset comparisons split width changes across inner and outer edges before applying the offset difference. Results are measurement aids, not vehicle approval. Confirm ratings, clearances and manufacturer guidance before fitting parts.