How to read a tyre size
Take 205/55 R16 91V as an example:
| Part | Means |
|---|---|
| 205 | Tyre width in millimetres, wall to wall. |
| 55 | Profile or aspect ratio: the sidewall height is 55% of the width, so 112.75mm. |
| R | Radial construction. Almost every car tyre is radial. |
| 16 | Wheel (rim) diameter in inches. |
| 91 | Load index: the most weight each tyre can carry, here 615kg. |
| V | Speed rating: the top sustained speed, here 149mph. |
You may also see XL or RF (extra load, a stronger tyre), RFT or similar (run-flat), and M+S or a snowflake symbol for winter and all-season tyres.
Speed rating table
| Symbol | Maximum speed |
|---|---|
| L | 75 mph (121 km/h) |
| M | 81 mph (130 km/h) |
| N | 87 mph (140 km/h) |
| P | 93 mph (150 km/h) |
| Q | 99 mph (159 km/h) |
| R | 106 mph (171 km/h) |
| S | 112 mph (180 km/h) |
| T | 118 mph (190 km/h) |
| U | 124 mph (200 km/h) |
| H | 130 mph (209 km/h) |
| V | 149 mph (240 km/h) |
| W | 168 mph (270 km/h) |
| Y | 186 mph (299 km/h) |
| (Y) | over 186 mph |
Load index table
| Index | Max load per tyre | Index | Max load per tyre |
|---|---|---|---|
| 70 | 335 kg | 91 | 615 kg |
| 71 | 345 kg | 92 | 630 kg |
| 72 | 355 kg | 93 | 650 kg |
| 73 | 365 kg | 94 | 670 kg |
| 74 | 375 kg | 95 | 690 kg |
| 75 | 387 kg | 96 | 710 kg |
| 76 | 400 kg | 97 | 730 kg |
| 77 | 412 kg | 98 | 750 kg |
| 78 | 425 kg | 99 | 775 kg |
| 79 | 437 kg | 100 | 800 kg |
| 80 | 450 kg | 101 | 825 kg |
| 81 | 462 kg | 102 | 850 kg |
| 82 | 475 kg | 103 | 875 kg |
| 83 | 487 kg | 104 | 900 kg |
| 84 | 500 kg | 105 | 925 kg |
| 85 | 515 kg | 106 | 950 kg |
| 86 | 530 kg | 107 | 975 kg |
| 87 | 545 kg | 108 | 1000 kg |
| 88 | 560 kg | 109 | 1030 kg |
| 89 | 580 kg | 110 | 1060 kg |
| 90 | 600 kg |
Fitting a different size
Keep the overall diameter within about 3% of the original, or the speedometer and ABS readings will be off. Never fit a lower load index or speed rating than the car's handbook states: it can invalidate your insurance and is a reason for an MOT failure if the tyre is not suitable for the vehicle.
Legal tread depth
The legal minimum for cars in the UK is 1.6mm across the central three-quarters of the tread, all the way round. The penalty is up to £2,500 and 3 points per tyre. Many experts recommend replacing at 3mm, because wet braking distances grow quickly below that.
Sources
Rates and rules last checked 15 October 2026. These figures are a guide. For a decision that matters, confirm with the official source.