155/70R13 tyre size
547.2 mm diameter
21.54 in · 108.5 mm sidewall · 1.72 m rolling circumference · 582 rev/km
Reading 155/70R13
| 155 | Tread width in millimetres |
| 70 | Aspect ratio — sidewall height as a percentage of the width, so 155 × 70% = 108.5 mm |
| R | Radial construction, which is almost every road tyre made since the 1970s |
| 13 | Rim diameter in inches — 330.2 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 155/70R13 and a size with a smaller aspect number on a larger rim can be the same overall diameter.
The numbers
| Tread width | 155 mm · 6.10 in |
| Sidewall height | 108.5 mm · 4.27 in |
| Rim diameter | 13 in · 330.2 mm |
| Overall diameter | 547.2 mm · 21.54 in |
| Rolling circumference | 1719.1 mm · 1.72 m |
| Revolutions per kilometre | 582 |
| Revolutions per mile | 936 |
Frequently asked questions
What does 155/70R13 mean?
155 is the tread width in millimetres, 70 is the sidewall height as a percentage of that width — so 155 × 70% = 108.5 mm of sidewall — and R13 is a radial tyre on a 13-inch rim. Overall diameter is 13 × 25.4 + 2 × 108.5 = 547.2 mm.
What is the overall diameter of a 155/70R13?
547.2 mm (21.54 inches), with a rolling circumference of 1.72 m — about 582 revolutions per kilometre.
Is 155/70R13 an unusual size?
Nothing else in this list is within 1% of its diameter, so replacements need checking against the vehicle's placard rather than picked by eye.
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.