How to use the chart
- Choose the rim diameter of your wheels.
- Find your current size and note its overall diameter.
- Look at the sizes within about 3% of it: they are the usual candidates for a swap on the same wheels.
- Open a pair in the comparison to see the drawing and the speedometer change.
Popular sizes and their diameter
| Size | Diameter (in) | Diameter (mm) |
|---|---|---|
| 175/70R14 | 23.65 | 600.6 |
| 185/65R15 | 24.47 | 621.5 |
| 195/60R15 | 24.21 | 615.0 |
| 205/55R16 | 24.88 | 631.9 |
| 215/65R16 | 27.00 | 685.9 |
| 225/45R17 | 24.97 | 634.3 |
| 225/65R17 | 28.52 | 724.3 |
| 235/60R18 | 29.10 | 739.2 |
| 245/75R16 | 30.47 | 773.9 |
| 265/70R16 | 30.61 | 777.4 |
| 245/75R17 | 31.47 | 799.3 |
| 265/70R17 | 31.61 | 802.8 |
| 285/70R17 | 32.71 | 830.8 |
| 275/55R20 | 31.91 | 810.5 |
| 275/60R20 | 32.99 | 838.0 |
How the chart is built
Every value comes from one formula: rim diameter plus two sidewalls, where each sidewall is the width times the aspect ratio. No catalogue of tire models is involved, so the chart can list sizes that are rarely sold, and real tires of the same size differ by a few millimeters between brands.
Reading the chart
On the same rim, a lower aspect ratio means a shorter tire, and at the same ratio a wider tire is taller. On 17 in rims, 225/45R17 is 24.97 in tall and 225/65R17 is 28.52 in: same width, about 3.5 in apart. Bigger rims do not mean taller tires either: 205/55R16 and 225/45R17 are almost the same height.
Sizes in inches use their nominal diameter: a 33x12.50R17 counts as 33.0 in (838.2 mm). Use the converter to find their metric neighbors.
Questions
What size tire is 31 inches?
On 17 in rims, 265/70R17 (31.61 in) and 245/75R17 (31.47 in) are the closest common metric sizes. On 15 in rims, the usual choice is the inch size 31x10.50R15.
Does a bigger rim mean a bigger tire?
Not necessarily. The overall diameter depends on the sidewall too: 205/55R16 is 24.88 in tall and 225/45R17 is 24.97 in.
Why does my tire measure differently from the chart?
The chart shows nominal values. Brand, tread pattern, rim width, inflation and wear all change the real size by a few millimeters.