What Size Tyre Do I Need?

Each tyre has standard markings that allow you to pick the right type for your car. It’s a confusing mix of letters and numbers, and of measurements in mm and inches.

All cars manufactured since 1973 have a placard containing information about correct tyre use. This placard indicates recommended tyre sizes, correct inflation pressures for front and rear tyres under normal driving, heavy loads and sustained high-speed operation. The placard is usually contained in the glove box, on the driver’s door pillar or under the front bonnet.

Here’s what it all means, using the code from the tyre below, P185/75R14 82S:

  • P — stands for passenger tyre.
  • 185 — this is the section width (in mm) when the tyre is fitted to the recommended rim, and inflated to the recommended pressure, and not under load. The section width is the distance between the tyre’s exterior sidewalls.
  • 75 — this is a percentage describing the tyre’s profile or aspect ratio. It’s the ratio between the tyre’s section height (distance from the wheel bead seat to the top of the tyre) and its section width — in this case 75%.
  • R — stands for radial, which is the most common construction method for passenger car tyres.
  • 14 — this refers to the diameter (in inches) of the rim the tyre should be fitted to.
  • 82 — this is the load rating index and tells you the maximum weight one tyre can carry (in this case it means 475 kg). Other examples include: 84 (500 kg), 86 (530 kg), 89 (580 kg), 93 (650 kg), 95 (690 kg).
  • S — this is the speed rating index and tells you the maximum speed the tyre can travel at (in this case 180 km/h). Other examples include: T (190 km/h), H (210 km/h), W (270 km/h).