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. Here’s what it all means, using the code for the tested size, P195/65R15 91V:
P — stands for passenger tyre.
195 — 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.
65 — 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 65%.
R — stands for radial, which is the most common construction method for passenger car tyres.
15 — this refers to the diameter (in inches) of the rim the tyre should be fitted to.
91 — this is the load rating index and tells you the maximum weight one tyre can carry (in this case it means 615 kg). Other examples: 84 (500 kg), 86 (530 kg), 89 (580 kg), 93 (650 kg), 95 (690 kg).
V — this is the speed rating index and tells you the maximum speed the tyre can travel at (in this case 240 km/h). Other examples: S (180 km/h), T (190 km/h), H (210 km/h), W (270 km/h).
How old is my tyre?
All tyres are stamped with the date of manufacture. You'll see this in two varieties: 3 digits for pre-2000, and 4 digits for after 2000.
Pre-2000: the first 2 digits stand for the week in the year and the last digit stands for the year. So a 3 digit of 078 stands for the seventh week in 1998.
After-2000: the first two digits stand for the week in the year and the last two digits stand for the year. So a 4 digit of 0209 stands for the second week in 2009.
Tread wear rating
Tyre models that are marketed in the US have to have a tread wear rating as part of the Uniform Tyre Quality Grading System (UTQG) operated by the US government National Highway Traffic Safety Administration. If the same tyre is available here you can use the information too. It's printed on the tyre sidewall.
Under the system, a tyre’s tread wear is measured under controlled conditions involving an 11,500 km drive on a specified test course, and compared to a ‘standard’ tyre with a rating of 100. A rating of 200 indicates that the tested tyre should last twice as long as the standard model. So the higher the number, the longer you can expect a tyre to last.
However, the rating is comparative only. Real-life wear of a tyre depends on a number of aspects, such as the road surface, tyre pressure, wheel alignment and driving style.
Also part of the UTQG, and printed on the tyre sidewall next to the tread wear rating, are:
- A traction rating that grades the tyre’s wet braking traction (AA, A, B or C, with AA being best).
- A temperature rating, which indicates a tyre’s ability to dissipate heat (A, B, C, with A being best).
Special tyre designs
- Some tyres are one-directional, which means they’re designed to be fitted to the car so their tread pattern faces a particular way (usually marked with an arrow on the sidewall). Fitting them on the wrong side may affect the car’s handling and reduce the tyre’s life. These are usually premium tyres. If you use these and don’t have a conventional tyre as a spare, be aware that a one-directional spare only fits one side of the car. If you have to use it on the wrong side, drive carefully and replace the damaged tyre as quickly as you can.
- Don’t confuse one-directional tyres with asymmetric models designed to be fitted to the rim so that a particular side (marked on the tyre’s sidewall) faces outwards. With these, the spare can replace any of the other tyres.
- Some car models have an emergency space-saver (narrower) spare instead of a full-size one. If you have to use it, follow the instructions in your user manual. There’s likely to be a speed limitation, and you’re only supposed to drive on it for a short distance to get you home or to the nearest tyre fitter. If you use it over longer distances or at higher speeds, you may damage your car.