305/30R21 — what does it mean?
- 305 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
- 21 is a wheel diameter (or rim) in inches
How to convert 305 30R21 to inches?
First of all, we need to divide 305 mm (width) by 25.4 (mm to inch conversion), which will give us a width of 12″. Then, 30% of the 12″ will result in 3.6″ sidewall.
To get the total height or tire diameter, we need to sum the 21″ rim diameter with two of the sidewall heights. It will result in a 28.2″ total tire diameter (or height).
For your convenience, below is a table for 305/30R21 conversion to inches:
| Inches | Metric | |
|---|---|---|
| Overall diameter (height) | 28.2″ | 716 mm |
| Tread width | 12″ | 305 mm |
| Wheel diameter | 21″ | 716 mm |
| Sidewall height | 3.6″ | 92 mm |
| Circumference | 88.5″ | 2248 mm |
| Revolutions | 716 / ml | 445 / km |
Alternatives to a 305/30R21 tire
If you're looking to upsize your 305 30R21 tires, try to stay within 3% deviation of an overall diameter for safety reasons.
| Tire | Tire diameter | Width | Wheel Size |
|---|---|---|---|
| 235/35R21 | 27.4″ -0.71% | 9.3″ | 21″ |
| 245/35R21 | 27.8″ -0.35% | 9.6″ | 21″ |
| 245/40R21 | 28.8″ 0.55% | 9.6″ | 21″ |
| 255/35R21 | 28″ -0.18% | 10″ | 21″ |
| 255/40R21 | 29″ 0.72% | 10″ | 21″ |
| 265/35R21 | 28.4″ 0.17% | 10.4″ | 21″ |
| 275/30R21 | 27.6″ -0.53% | 10.8″ | 21″ |
| 275/35R21 | 28.6″ 0.35% | 10.8″ | 21″ |
| 285/30R21 | 27.8″ -0.35% | 11.2″ | 21″ |
| 285/35R21 | 28.8″ 0.55% | 11.2″ | 21″ |