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.
Set your size and see the real dimensions
Did you know?
Read the date code on your tire: if it has only 3 digits, the tire was made before 2000, so it is more than 26 years old.
Dates checked on two independent sources each.
- 1946Radial X Michelin's X, its radial car tire, dates from 1946.
- 1979UTQG US tire quality grades for treadwear, traction and temperature (UTQG) take effect.
- 20004-digit DOT The DOT date code on the sidewall grows to 4 digits: two for the week, two for the year.
- 2007TPMS Tire pressure monitoring (TPMS) becomes mandatory on all new light vehicles in the US.
Sources (two per date)
- 1946: Michelin · The Drive
- 1979: Tire Review · NHTSA
- 2000: Tire Rack · Federal Register
- 2007: Schrader TPMS Solutions · Federal Register