Industry Guide
How to Read Tire Sizes: Width, Ratio, and Diameter
Decode tire size markings and understand what each number means for your vehicle.
Last updated: 2026-03-15
Tire Size Breakdown: 225/65R17 91H
| Code | Meaning | Value |
|---|---|---|
| 225 | Tire width | 225 mm (8.86 in) |
| 65 | Aspect ratio | Sidewall = 65% of width |
| R | Construction | Radial |
| 17 | Wheel diameter | 17 inches |
| 91 | Load index | 1,356 lbs (615 kg) per tire |
| H | Speed rating | 130 mph (210 km/h) max |
Overall Diameter Calculation
Diameter (in) = (2 × Width mm × Aspect% / 2,540) + Wheel diameter
Example: 225/65R17
- Sidewall height: 225 × 0.65 = 146.25 mm = 5.758 inches
- Overall diameter: (2 × 5.758) + 17 = 28.52 inches (724.4 mm)
- Circumference: 28.52 × π = 89.6 inches = 7.47 feet
Common Tire Sizes Reference
| Tire Size | Width (in) | Sidewall (in) | Diameter (in) |
|---|---|---|---|
| 195/65R15 | 7.68 | 4.99 | 24.98 |
| 205/55R16 | 8.07 | 4.44 | 24.88 |
| 215/60R16 | 8.46 | 5.08 | 26.16 |
| 225/65R17 | 8.86 | 5.76 | 28.52 |
| 235/55R18 | 9.25 | 5.09 | 28.18 |
| 245/75R16 | 9.65 | 7.24 | 30.47 |
| 265/70R17 | 10.43 | 7.30 | 31.61 |
Speed Ratings
| Rating | Max Speed (mph) | Max Speed (km/h) |
|---|---|---|
| S | 112 | 180 |
| T | 118 | 190 |
| H | 130 | 210 |
| V | 149 | 240 |
| W | 168 | 270 |
| Y | 186 | 300 |
Convert tire dimensions with our length converter.