1) OEM (stock)
Find OEM pressure on the door pillar or fuel flap. Sidewall example: 225/45R17 94Y XL.
2) New setup (aftermarket)
Corrections are applied on top of the calculated base pressure.
3) Result
About speed index
The speed index (letter after the size, e.g. 91V) indicates the max speed the tire is designed for. We apply a small correction: 200–240 km/h ≈ +0.2 bar; ≥270 km/h ≈ +0.4 bar. Z (240+) is treated as +0.3 bar. Always verify with the tire manufacturer.
| Index | Max speed (km/h) | Typical vehicle |
|---|---|---|
| L | 120 | Off-road, light truck |
| M | 130 | Temporary spare |
| N | 140 | Temporary spare |
| P | 150 | — |
| Q | 160 | Winter 4×4 |
| R | 170 | Trucks |
| S | 180 | Saloons, vans |
| T | 190 | Saloons, vans |
| U | 200 | Saloons, coupés |
| H | 210 | Sport saloons |
| V | 240 | Sports cars |
| Z | 240+ | Sports cars |
| W | 270 | Luxury sports cars |
| Y | 300 | Luxury sports cars |
| (Y) | 300+ | Luxury sports cars |
How to Read Your Tire Size
If you’re unsure which tires are fitted to your vehicle, the complete size and rating information is printed on the tire’s sidewall. A typical sequence looks like 195/65 R15 91T. Each element has a specific meaning:
Tire width (e.g. 195)
The section width in millimeters when properly inflated. Passenger-car tires typically range from 125 mm to 335 mm, in 10 mm steps.
Aspect ratio / sidewall height (e.g. 65)
The sidewall height as a percentage of the width. In this example, 65 means the height is 65% of 195 mm.
Construction type (R)
R indicates a radial tire — the modern standard, where steel cord plies run radially for flexibility and consistent road contact.
Rim diameter (e.g. 15)
The rim diameter in inches that the tire fits. One inch equals 25.4 mm. Many modern cars use 15–19 inch wheels for handling and load capacity.
Load index (e.g. 91)
A number indicating the maximum load per tire. For example, 91 = 615 kg. Always fit tires with at least the OEM load index — especially if your vehicle specifies XL (Extra Load).
Speed index (e.g. T)
A letter indicating the maximum speed for the tire (e.g., T = up to 190 km/h). Never go below the manufacturer’s recommendation; higher ratings are acceptable.
Other markings you may see
- RunFlat — can drive short distances after a puncture; use only on vehicles with TPMS.
- Extra Load (XL) — reinforced tires with higher load capacity (common on SUVs, vans, caravans).
- Tubeless (TL) — tire without an inner tube; nearly all modern passenger tires are tubeless.