225/55R17 tyre size
679.3 mm diameter
26.74 in · 123.8 mm sidewall · 2.13 m rolling circumference · 469 rev/km
Reading 225/55R17
| 225 | Tread width in millimetres |
| 55 | Aspect ratio — sidewall height as a percentage of the width, so 225 × 55% = 123.8 mm |
| R | Radial construction, which is almost every road tyre made since the 1970s |
| 17 | Rim diameter in inches — 431.8 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 225/55R17 and a size with a smaller aspect number on a larger rim can be the same overall diameter.
The numbers
| Tread width | 225 mm · 8.86 in |
| Sidewall height | 123.8 mm · 4.87 in |
| Rim diameter | 17 in · 431.8 mm |
| Overall diameter | 679.3 mm · 26.74 in |
| Rolling circumference | 2134.1 mm · 2.13 m |
| Revolutions per kilometre | 469 |
| Revolutions per mile | 754 |
Sizes that fit in place of 225/55R17
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 |
|---|---|---|---|
| 245/45R18 | 677.7 mm | -0.24% | 99.8 km/h actual |
| 275/35R19 | 675.1 mm | -0.62% | 99.4 km/h actual |
| 205/65R16 | 672.9 mm | -0.94% | 99.1 km/h actual |
| 215/65R16 | 685.9 mm | +0.97% | 101.0 km/h actual |
| 255/40R19 | 686.6 mm | +1.07% | 101.1 km/h actual |
| 255/45R18 | 686.7 mm | +1.09% | 101.1 km/h actual |
| 215/60R17 | 689.8 mm | +1.55% | 101.5 km/h actual |
| 215/55R17 | 668.3 mm | -1.62% | 98.4 km/h actual |
| 235/55R17 | 690.3 mm | +1.62% | 101.6 km/h actual |
| 305/30R20 | 691.0 mm | +1.72% | 101.7 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 17-inch sizes
| Size | Sidewall | Diameter |
|---|---|---|
| 205/50R17 | 102.5 mm | 636.8 mm |
| 215/45R17 | 96.8 mm | 625.3 mm |
| 215/55R17 | 118.3 mm | 668.3 mm |
| 215/60R17 | 129.0 mm | 689.8 mm |
| 225/45R17 | 101.3 mm | 634.3 mm |
| 225/50R17 | 112.5 mm | 656.8 mm |
| 225/60R17 | 135.0 mm | 701.8 mm |
| 225/65R17 | 146.3 mm | 724.3 mm |
Frequently asked questions
What does 225/55R17 mean?
225 is the tread width in millimetres, 55 is the sidewall height as a percentage of that width — so 225 × 55% = 123.8 mm of sidewall — and R17 is a radial tyre on a 17-inch rim. Overall diameter is 17 × 25.4 + 2 × 123.8 = 679.3 mm.
What is the overall diameter of a 225/55R17?
679.3 mm (26.74 inches), with a rolling circumference of 2.13 m — about 469 revolutions per kilometre.
What size is equivalent to a 225/55R17?
245/45R18 (-0.24%), 275/35R19 (-0.62%), 205/65R16 (-0.94%) — 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.