265/60R18 tyre size
775.2 mm diameter
30.52 in · 159.0 mm sidewall · 2.44 m rolling circumference · 411 rev/km
Reading 265/60R18
| 265 | Tread width in millimetres |
| 60 | Aspect ratio — sidewall height as a percentage of the width, so 265 × 60% = 159.0 mm |
| R | Radial construction, which is almost every road tyre made since the 1970s |
| 18 | Rim diameter in inches — 457.2 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 265/60R18 and a size with a smaller aspect number on a larger rim can be the same overall diameter.
The numbers
| Tread width | 265 mm · 10.43 in |
| Sidewall height | 159.0 mm · 6.26 in |
| Rim diameter | 18 in · 457.2 mm |
| Overall diameter | 775.2 mm · 30.52 in |
| Rolling circumference | 2435.4 mm · 2.44 m |
| Revolutions per kilometre | 411 |
| Revolutions per mile | 661 |
Sizes that fit in place of 265/60R18
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 |
|---|---|---|---|
| 265/65R17 | 776.3 mm | +0.14% | 100.1 km/h actual |
| 265/70R16 | 777.4 mm | +0.28% | 100.3 km/h actual |
| 275/45R20 | 755.5 mm | -2.54% | 97.5 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.
Other 18-inch sizes
| Size | Sidewall | Diameter |
|---|---|---|
| 225/40R18 | 90.0 mm | 637.2 mm |
| 235/40R18 | 94.0 mm | 645.2 mm |
| 235/60R18 | 141.0 mm | 739.2 mm |
| 245/40R18 | 98.0 mm | 653.2 mm |
| 245/45R18 | 110.3 mm | 677.7 mm |
| 255/45R18 | 114.8 mm | 686.7 mm |
| 255/55R18 | 140.3 mm | 737.7 mm |
Frequently asked questions
What does 265/60R18 mean?
265 is the tread width in millimetres, 60 is the sidewall height as a percentage of that width — so 265 × 60% = 159.0 mm of sidewall — and R18 is a radial tyre on a 18-inch rim. Overall diameter is 18 × 25.4 + 2 × 159.0 = 775.2 mm.
What is the overall diameter of a 265/60R18?
775.2 mm (30.52 inches), with a rolling circumference of 2.44 m — about 411 revolutions per kilometre.
What size is equivalent to a 265/60R18?
265/65R17 (+0.14%), 265/70R16 (+0.28%) — 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.