How to read a tire size
Everything on the sidewall, from left to right, with one example: P225/65R17 102H.
- P
- Passenger car tire. LT means light truck. Many tires show no letter.
- 225
- Width, sidewall to sidewall, in millimetres.
- 65
- Aspect ratio: the sidewall height is 65 percent of the width.
- R
- Radial construction.
- 17
- Wheel diameter, in inches.
- 102
- Load index: the most weight one tire may carry. In Volvo's example, 95 equals 1,521 lb (690 kg). Load index chart.
- H
- Speed rating: the highest speed the tire is built for (table below, every letter in the speed rating chart).
Speed ratings
| Letter | Up to | Metric |
|---|---|---|
| M | 81 mph | 130 km/h |
| Q | 99 mph | 160 km/h |
| T | 118 mph | 190 km/h |
| H | 130 mph | 210 km/h |
| V | 149 mph | 240 km/h |
| W | 168 mph | 270 km/h |
| Y | 186 mph | 300 km/h |
The DOT date code
The DOT number ends with four digits: the week and the year the tire was made. 0717 means week 7 of 2017. Rubber ages even when the tread looks fine, so check this date on any used tire.
How much tread is left
NHTSA recommends replacing tires at 2/32 of an inch of tread, and earlier, around 4/32, for better grip in rain and snow. The penny test: put a penny in the tread with Lincoln's head upside down. If you can see all of his head, there is 2/32 or less left. The small bars across the grooves are wear indicators: when the tread is level with them, the tire is worn out.
Sources: Volvo Cars Support, "Tire sidewall designations" (volvocars.com), read October 14, 2026; Ford Support, "Why does tread wear matter on my Ford?" (ford.com), citing NHTSA, read October 14, 2026.