285/45R22 tyre size
815.3 mm diameter
32.10 in · 128.3 mm sidewall · 2.56 m rolling circumference · 390 rev/km
Reading 285/45R22
| 285 | Tread width in millimetres |
| 45 | Aspect ratio — sidewall height as a percentage of the width, so 285 × 45% = 128.3 mm |
| R | Radial construction, which is almost every road tyre made since the 1970s |
| 22 | Rim diameter in inches — 558.8 mm |
The aspect ratio is the part that catches people: it is a percentage of the width, not a fixed height. Widen the tread and keep the same aspect number and the tyre also gets taller. That is why 285/45R22 and a size with a smaller aspect number on a larger rim can be the same overall diameter.
The numbers
| Tread width | 285 mm · 11.22 in |
| Sidewall height | 128.3 mm · 5.05 in |
| Rim diameter | 22 in · 558.8 mm |
| Overall diameter | 815.3 mm · 32.10 in |
| Rolling circumference | 2561.3 mm · 2.56 m |
| Revolutions per kilometre | 390 |
| Revolutions per mile | 628 |
Sizes that fit in place of 285/45R22
A replacement is judged on rolling diameter, because that is what the speedometer, the ABS and the gearing all depend on. Anything within about 1% is treated as interchangeable; beyond 3% the speedometer error stops being ignorable.
| Size | Diameter | Difference | Speedometer at an indicated 100 |
|---|---|---|---|
| 275/55R20 | 810.5 mm | -0.59% | 99.4 km/h actual |
| 265/70R17 | 802.8 mm | -1.53% | 98.5 km/h actual |
Diameter is only half the question — the replacement also has to suit the rim width and the vehicle's load and speed ratings. Check the placard in the door frame before buying.
Frequently asked questions
What does 285/45R22 mean?
285 is the tread width in millimetres, 45 is the sidewall height as a percentage of that width — so 285 × 45% = 128.3 mm of sidewall — and R22 is a radial tyre on a 22-inch rim. Overall diameter is 22 × 25.4 + 2 × 128.3 = 815.3 mm.
What is the overall diameter of a 285/45R22?
815.3 mm (32.10 inches), with a rolling circumference of 2.56 m — about 390 revolutions per kilometre.
What size is equivalent to a 285/45R22?
275/55R20 (-0.59%) — all within 1% of this diameter, which is the band inside which a manufacturer will list alternatives for the same car. Width and rim differ; rolling diameter does not.
How much does changing tyre size affect the speedometer?
A speedometer counts wheel revolutions, so it reads in proportion to the rolling diameter it was calibrated for. Fitting a tyre 1% larger makes the speedometer read 1% low — at an indicated 100 km/h you are doing 101. Most jurisdictions expect a speedometer to never under-read, which is why replacements are kept within about 3% and why the factory tyre usually reads a little high to begin with.