How to Read the Numbers on Your Tyre Sidewall
Every tyre has a string of letters and numbers moulded into its sidewall. It looks like code because it is one, and once you can read it you can check that a tyre fits your car, carries enough weight and is rated for the speeds you drive. Here is the most common example: 205/55 R16 91V.
Short version: 205 is the width in millimetres, 55 is the sidewall height as a percentage of that width, R means radial, 16 is the wheel size in inches, 91 is the load index and V is the speed rating.
Width: 205
The first number is the width of the tread in millimetres, measured from one sidewall edge to the other. A 205 tyre is about 20.5 centimetres wide. A wider tyre puts more rubber on the road, but it is not automatically better. Your car was designed around a small range of widths, and going outside that range can cause rubbing against the bodywork or suspension.
Aspect ratio: 55
The second number, after the slash, is the height of the sidewall expressed as a percentage of the width. Here the sidewall is 55 percent of 205 mm, which is roughly 113 mm. A lower number means a shorter, stiffer sidewall. A higher number means a taller sidewall that absorbs more of the bumps, which is useful on rough or potholed roads.
Construction: R
R stands for radial, which describes how the internal cords are laid. Nearly all modern car tyres are radial. You may occasionally see a D (diagonal or bias-ply) on older or specialist tyres.
Rim diameter: 16
This is the diameter of the wheel the tyre fits, in inches. It must match your wheel exactly. A 16-inch tyre cannot be fitted on a 15-inch or 17-inch wheel.
Load index: 91
The load index is a code for the maximum weight one tyre can carry when correctly inflated. It is not the weight itself. Index 91 means 615 kg per tyre. You can look up the full chart, but these are common values:
| Load index | Maximum load per tyre |
|---|---|
| 82 | 475 kg |
| 88 | 560 kg |
| 91 | 615 kg |
| 95 | 690 kg |
| 100 | 800 kg |
Never fit a tyre with a lower load index than the one your car maker specifies. If you regularly carry heavy loads or passengers, a higher index gives you more margin.
Speed rating: V
The final letter is the top speed the tyre is designed to sustain. V is 240 km/h. Other common ratings are:
| Letter | Maximum speed |
|---|---|
| S | 180 km/h |
| T | 190 km/h |
| H | 210 km/h |
| V | 240 km/h |
| W | 270 km/h |
You are unlikely to drive at these speeds, but the rating also reflects how well the tyre handles heat and stress, so stay at or above what your manual recommends.
Other markings you may see
- XL or Reinforced: an extra-load tyre built to carry more weight at the same size.
- M+S: mud and snow rating. Common on all-season and SUV tyres.
- DOT code: a manufacturing code that ends with four digits showing the week and year the tyre was made. See our guide on how to check how old a tyre is.
- Tubeless: the tyre seals directly against the rim and needs no inner tube.
Where to find the size your car needs
Do not guess from the tyres currently on the car, because a previous owner may have fitted the wrong size. Look for the tyre placard on the driver's door jamb, inside the fuel flap or in the owner's manual. It lists the correct size, load index and recommended pressures.