315/35R21 vs 285/35R22
285/35R22 is a safe swap for 315/35R21 by the usual ±3% rule: the diameter differs by +0.58%.
Speedometer and odometer
With 285/35R22 on a car calibrated for 315/35R21, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.5 mph |
Other sizes close to 315/35R21
- 315/35R21 vs 245/50R20-0.12%
- 315/35R21 vs 275/45R20+0.21%
- 315/35R21 vs 265/45R20-0.98%
- 315/35R21 vs 265/40R21-1.13%
- 315/35R21 vs 275/35R21-3.71%
- 315/35R21 vs 295/35R21-1.86%
- 315/35R21 vs 275/45R21+3.58%
- 315/35R21 vs 255/40R21-2.19%
- 315/35R21 vs 265/35R21-4.64%
- 315/35R21 vs 295/40R21+2.06%
- 315/35R21 vs 285/45R21+4.78%
- 315/35R21 vs 285/40R21+0.99%
Questions
Can I replace 315/35R21 with 285/35R22?
285/35R22 is a safe swap for 315/35R21 by the usual ±3% rule: the diameter differs by +0.58%.
What's the difference between 315/35R21 and 285/35R22?
285/35R22 is 0.17" taller and 30 mm narrower; the sidewall is -0.41". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 285/35R22 fit on 315/35R21 wheels?
No — 315/35R21 needs a 21" wheel and 285/35R22 a 22" wheel. This is a plus/minus-size swap that changes wheels too.