P315/30R18 — what does it mean?
- P means "passenger car"
- 315 stands for tread width in millimeters
- 30 is an aspect ration between the tread width and the sidewall in percents
- R means that the tire has a radial construction
- 18 is a wheel diameter (or rim) in inches
How to convert P315 30R18 to inches?
First of all, we need to divide 315 mm (width) by 25.4 (mm to inch conversion), which will give us a width of 12.4″. Then, 30% of the 12.4″ will result in 3.7″ sidewall.
To get the total height or tire diameter, we need to sum the 18″ rim diameter with two of the sidewall heights. It will result in a 25.4″ total tire diameter (or height).
For your convenience, below is a table for P315/30R18 conversion to inches:
| Inches | Metric | |
|---|---|---|
| Overall diameter (height) | 25.4″ | 645 mm |
| Tread width | 12.4″ | 315 mm |
| Wheel diameter | 18″ | 645 mm |
| Sidewall height | 3.7″ | 95 mm |
| Circumference | 79.8″ | 2025 mm |
| Revolutions | 795 / ml | 494 / km |
Alternatives to a P315/30R18 tire
If you're looking to upsize your P315 30R18 tires, try to stay within 3% deviation of an overall diameter for safety reasons.
| Tire | Tire diameter | Width | Wheel Size |
|---|---|---|---|
| 245/40R18 | 25.8″ 0.38% | 9.6″ | 18″ |
| 125/70R18 | 25″ -0.39% | 4.9″ | 18″ |
| 135/70R18 | 25.4″ 0% | 5.3″ | 18″ |
| 145/65R18 | 25.4″ 0% | 5.7″ | 18″ |
| 145/70R18 | 26″ 0.57% | 5.7″ | 18″ |
| 155/60R18 | 25.4″ 0% | 6.1″ | 18″ |
| 185/55R18 | 26″ 0.57% | 7.3″ | 18″ |
| 205/45R18 | 25.2″ -0.19% | 8.1″ | 18″ |
| 205/50R18 | 26.2″ 0.76% | 8.1″ | 18″ |
| 215/40R18 | 24.8″ -0.59% | 8.5″ | 18″ |