How to read a tire size
Take the size P225/65R17 102H as an example. Each part tells you something different.
| P | Tire type: P for passenger, LT for light truck, ST for trailer, none for European metric. |
|---|---|
| 225 | Section width in millimeters, sidewall to sidewall (8.86 inches). |
| 65 | Aspect ratio: the sidewall is 65% as tall as the tire is wide (5.76 inches). |
| R | Radial construction. |
| 17 | Wheel (rim) diameter in inches. |
| 102 | Load index: 1,874 lbs per tire. |
| H | Speed rating: up to 130 mph. |
Working out the height
Sidewall = 225 × 0.65 = 146.25 mm. There are two sidewalls, so 292.5 mm, or 11.52 inches. Add the 17 inch wheel and the tire is 28.52 inches tall. Our tire size calculator does this for any size.
Flotation sizes
Off-road truck tires are often sized like 33x12.50R20: 33 inches tall, 12.5 inches wide, for a 20 inch wheel. No math needed.
The date code
The DOT code on the sidewall ends with four digits showing the week and year the tire was made. Decode yours here.
Questions
- What does the P or LT before a tire size mean?
- P means a passenger car tire (P-metric). LT means light truck, built for heavier loads and higher pressures. No letter means a European (Euro-metric) size, which is the same dimensions as P.
- What does R mean in a tire size?
- R means radial construction, which almost every modern tire uses. D or B means bias-ply, found on some trailer and specialty tires.
- Is the aspect ratio the sidewall height?
- It is the sidewall height as a percentage of the width. A 225/65 tire has a sidewall 65% of 225 mm, or 146 mm. The lower the number, the shorter (lower-profile) the sidewall.