Quick Answer
- 225/55R17 reads: 225 mm section width, sidewall 55% of that width, R for radial, 17 inch rim. Add 91V and the 91 is the load index and V the speed rating.
- Overall diameter = rim + 2 x sidewall: 17 + 2 x 123.75 mm / 25.4 = 26.74 in. Width is 225 / 25.4 = 8.86 in.
- A metric size is not an inch size: for 33x12.50R17 the closest metric size is 315/65R17 (calculated), see the chart below.
To convert a size now, use the metric tire calculator.
What Each Part of a Metric Tire Size Means
Meanings from Michelin USA's tire markings guide; inches, pounds and speeds are calculated or from the load and speed tables.
| In P225/55R17 91V | Name | Meaning | Example |
|---|---|---|---|
| P | Service type prefix | Michelin: P is passenger car, LT is light truck, C is commercial van, T is a temporary spare. XL, HL or Reinforced mark tires built to carry higher loads. | P225/55R17 |
| 225 | Section width | Nominal section width in millimetres. | 8.86 in |
| 55 | Aspect ratio | Sidewall height as a percentage of the width. | 123.75 mm sidewall |
| R | Construction | R is radial construction. | Radial |
| 17 | Rim diameter | Wheel diameter in inches. It must match your wheel. | 17 in |
| 91 V | Service description | Load rating and speed rating. The load rating is the maximum weight one tire can carry when properly inflated; the speed rating is the maximum speed at which it can carry that load under specified conditions. | 1355 lb, 149 mph |
Converting a Metric Tire Size to Inches
1. Sidewall height in mm
Width x aspect / 100. For 225/55: 225 x 55 / 100 = 123.75 mm.
2. Sidewall in inches
Divide by 25.4: 123.75 / 25.4 = 4.87 in.
3. Overall diameter
Rim + 2 x sidewall = 17 + 2 x 4.87 = 26.74 in (679 mm).
4. Circumference and revs
Pi x diameter = 84.0 in, and 63,360 / circumference = 754 revs per mile.
How the Aspect Ratio Changes the Diameter
A 225 mm wide tire on a 17 inch rim, changing only the aspect ratio. Calculated.
| Size | Sidewall in | Overall diameter in |
|---|---|---|
| 225/35R17 | 3.10 | 23.20 |
| 225/40R17 | 3.54 | 24.09 |
| 225/45R17 | 3.99 | 24.97 |
| 225/50R17 | 4.43 | 25.86 |
| 225/55R17 | 4.87 | 26.74 |
| 225/60R17 | 5.31 | 27.63 |
| 225/65R17 | 5.76 | 28.52 |
Metric Tire Sizes in Inches
Calculated overall dimensions for common sizes.
| Size | Width in | Sidewall in | Diameter in | Diameter mm | Rim in |
|---|---|---|---|---|---|
| 195/65R15 | 7.68 | 4.99 | 24.98 | 635 | 15 |
| 205/55R16 | 8.07 | 4.44 | 24.88 | 632 | 16 |
| 215/60R16 | 8.46 | 5.08 | 26.16 | 664 | 16 |
| 225/55R17 | 8.86 | 4.87 | 26.74 | 679 | 17 |
| 225/65R17 | 8.86 | 5.76 | 28.52 | 724 | 17 |
| 235/55R18 | 9.25 | 5.09 | 28.18 | 716 | 18 |
| 245/45R18 | 9.65 | 4.34 | 26.68 | 678 | 18 |
| 255/55R19 | 10.04 | 5.52 | 30.04 | 763 | 19 |
| 265/70R17 | 10.43 | 7.30 | 31.61 | 803 | 17 |
| 275/65R18 | 10.83 | 7.04 | 32.07 | 815 | 18 |
| 285/70R17 | 11.22 | 7.85 | 32.71 | 831 | 17 |
| 315/70R17 | 12.40 | 8.68 | 34.36 | 873 | 17 |
| Width mm | Inches |
|---|---|
| 185 | 7.28 |
| 205 | 8.07 |
| 225 | 8.86 |
| 245 | 9.65 |
| 265 | 10.43 |
| 285 | 11.22 |
| 305 | 12.01 |
| 315 | 12.40 |
| Width in | mm |
|---|---|
| 10.5 | 266.7 |
| 11.5 | 292.1 |
| 12.5 | 317.5 |
| 13.5 | 342.9 |
| Diameter in | mm |
|---|---|
| 31 | 787 |
| 32 | 813 |
| 33 | 838 |
| 34 | 864 |
| 35 | 889 |
| 37 | 940 |
33 and 35 Inch Tires in Metric
Inch sizes are nominal, so these are the closest metric sizes (calculated). The full chart, with the method, is on the metric tire calculator.
| Inch size | Closest metric | Metric diameter | Difference |
|---|---|---|---|
| 31x10.50R15 | 265/75R15 | 30.6" | -0.4" |
| 33x12.50R15 | 315/70R15 | 32.4" | -0.6" |
| 33x12.50R17 | 315/65R17 | 33.1" | +0.1" |
| 35x12.50R17 | 315/70R17 | 34.4" | -0.6" |
| 35x12.50R18 | 305/70R18 | 34.8" | -0.2" |
| 37x12.50R17 | 315/80R17 | 36.8" | -0.2" |
Load Index and Speed Rating After the Size
Examples from the tables behind the load index calculator and the speed rating calculator. Michelin says replacements should meet or exceed the vehicle maker's ratings.
| Load index | Pounds | Kilograms |
|---|---|---|
| 85 | 1135 | 515 |
| 90 | 1325 | 600 |
| 95 | 1520 | 690 |
| 100 | 1765 | 800 |
| 105 | 2040 | 925 |
| 110 | 2335 | 1060 |
| Speed rating | mph | km/h |
|---|---|---|
| S | 112 | 180 |
| T | 118 | 190 |
| H | 130 | 210 |
| V | 149 | 240 |
| W | 168 | 270 |
| Y | 186 | 300 |
Frequently Asked Questions
Sources: Michelin USA, How to Read Tire Markings and Sidewall Codes; Bridgestone International Load Index table; Continental plus-sizing guidance. Dimensions are calculated. Also see the tire size guide and the plus sizing options calculator.