285/40R21 — what does it mean?
- 285 stands for tread width in millimeters
- 40 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 285 40R21 to inches?
First of all, we need to divide 285 mm (width) by 25.4 (mm to inch conversion), which will give us a width of 11.2″. Then, 40% of the 11.2″ will result in 4.5″ 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 30″ total tire diameter (or height).
For your convenience, below is a table for 285/40R21 conversion to inches:
| Inches | Metric | |
|---|---|---|
| Overall diameter (height) | 30″ | 762 mm |
| Tread width | 11.2″ | 285 mm |
| Wheel diameter | 21″ | 762 mm |
| Sidewall height | 4.5″ | 114 mm |
| Circumference | 94.2″ | 2393 mm |
| Revolutions | 673 / ml | 418 / km |
Alternatives to a 285/40R21 tire
If you're looking to upsize your 285 40R21 tires, try to stay within 3% deviation of an overall diameter for safety reasons.
| Tire | Tire diameter | Width | Wheel Size |
|---|---|---|---|
| 235/45R21 | 29.4″ -0.5% | 9.3″ | 21″ |
| 245/45R21 | 29.6″ -0.33% | 9.6″ | 21″ |
| 255/45R21 | 30″ 0% | 10″ | 21″ |
| 265/40R21 | 29.4″ -0.5% | 10.4″ | 21″ |
| 265/45R21 | 30.4″ 0.33% | 10.4″ | 21″ |
| 275/40R21 | 29.6″ -0.33% | 10.8″ | 21″ |
| 275/45R21 | 30.8″ 0.65% | 10.8″ | 21″ |
| 295/35R21 | 29.2″ -0.66% | 11.6″ | 21″ |
| 295/40R21 | 30.2″ 0.16% | 11.6″ | 21″ |
| 305/35R21 | 29.4″ -0.5% | 12″ | 21″ |