Free tool
Tire reference
What does your tire size mean?
Decode a tire size into its real geometry — sidewall height, overall diameter, circumference, load capacity and speed rating — or compare two sizes for plus-sizing, with the diameter difference, speedometer error and a clear ±3% verdict.
Load index table
See the full table →Each load index maps to the maximum weight one tire can carry at its rated pressure.
| Load index | Max load (per tire) |
|---|---|
| 60 | 250 kg |
| 61 | 257 kg |
| 62 | 265 kg |
| 63 | 272 kg |
| 64 | 280 kg |
| 65 | 290 kg |
| 66 | 300 kg |
| 67 | 307 kg |
| 68 | 315 kg |
| 69 | 325 kg |
| 70 | 335 kg |
| 71 | 345 kg |
| 72 | 355 kg |
| 73 | 365 kg |
| 74 | 375 kg |
| 75 | 387 kg |
| 76 | 400 kg |
| 77 | 412 kg |
| 78 | 425 kg |
| 79 | 437 kg |
| 80 | 450 kg |
| 81 | 462 kg |
| 82 | 475 kg |
| 83 | 487 kg |
| 84 | 500 kg |
| 85 | 515 kg |
| 86 | 530 kg |
| 87 | 545 kg |
| 88 | 560 kg |
| 89 | 580 kg |
| 90 | 600 kg |
| 91 | 615 kg |
| 92 | 630 kg |
| 93 | 650 kg |
| 94 | 670 kg |
| 95 | 690 kg |
| 96 | 710 kg |
| 97 | 730 kg |
| 98 | 750 kg |
| 99 | 775 kg |
| 100 | 800 kg |
| 101 | 825 kg |
| 102 | 850 kg |
| 103 | 875 kg |
| 104 | 900 kg |
| 105 | 925 kg |
| 106 | 950 kg |
| 107 | 975 kg |
| 108 | 1000 kg |
| 109 | 1030 kg |
| 110 | 1060 kg |
| 111 | 1090 kg |
| 112 | 1120 kg |
| 113 | 1150 kg |
| 114 | 1180 kg |
| 115 | 1215 kg |
| 116 | 1250 kg |
| 117 | 1285 kg |
| 118 | 1320 kg |
| 119 | 1360 kg |
| 120 | 1400 kg |
| 121 | 1450 kg |
| 122 | 1500 kg |
| 123 | 1550 kg |
| 124 | 1600 kg |
| 125 | 1650 kg |
| 126 | 1700 kg |
Speed rating chart
See the full table →The speed symbol is the maximum sustained speed the tire is approved for.
| Symbol | Max speed |
|---|---|
| J | 100 km/h |
| K | 110 km/h |
| L | 120 km/h |
| M | 130 km/h |
| N | 140 km/h |
| P | 150 km/h |
| Q | 160 km/h |
| R | 170 km/h |
| S | 180 km/h |
| T | 190 km/h |
| U | 200 km/h |
| H | 210 km/h |
| V | 240 km/h |
| W | 270 km/h |
| Y | 300 km/h |
How to read a tire size
A marking like 225/45 R17 94V follows the ISO/ETRTO standard printed on every passenger tire. The first number (225) is the section width in millimetres. The second (45) is the aspect ratio — the sidewall height as a percentage of the width — so a lower number means a shorter, sportier sidewall. The letter (R) means radial construction, and 17 is the rim diameter in inches. The trailing 94V is the service description: the load index (94 = 670 kg per tire) and the speed symbol (V = 240 km/h).
Overall diameter is what matters when you change sizes. Because the speedometer is calibrated to the original rolling circumference, fitting a taller tire makes the car travel further per wheel revolution than the speedometer assumes — so it under-reads, and you're actually going faster than it shows. The industry rule of thumb is to stay within ±3% of the original diameter when plus-sizing; beyond that, speedometer accuracy, ABS and stability-control calibration and clearance can all be affected.
Frequently asked questions
What does 225/45 R17 mean?
225 is the tire's section width in millimetres. 45 is the aspect ratio — the sidewall height is 45% of the width, so 101.25 mm here. R means radial construction, and 17 is the wheel (rim) diameter in inches. If there's a trailing code like 94V, 94 is the load index (670 kg per tire) and V is the speed symbol (good for up to 240 km/h).
Can I fit a wider or taller tire than the original?
Often yes, within limits. The usual plus-sizing rule is to keep the overall diameter within about ±3% of the original so the rolling circumference — and therefore speedometer accuracy, ABS calibration and clearance — stays close to what the car expects. Width and rim changes also need to fit the wheel and bodywork, and the new tire must meet or exceed the original load and speed ratings. Always check your vehicle's tire placard and a tire professional before fitting.
How does tire size affect my speedometer?
A speedometer measures wheel rotation and converts it to speed assuming the original tire's circumference. A taller tire travels further per revolution, so the speedometer under-reads — you're actually going faster than it shows. A shorter tire does the opposite. The percentage error equals the percentage change in overall diameter, which is exactly what the compare mode reports.