315/30R22 vs 275/40R21
275/40R21 is a safe swap for 315/30R22 by the usual ±3% rule: the diameter differs by +0.75%.
Speedometer and odometer
With 275/40R21 on a car calibrated for 315/30R22, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.6 mph |
Other sizes close to 315/30R22
- 315/30R22 vs 265/40R21-0.32%
- 315/30R22 vs 275/40R22+4.15%
- 315/30R22 vs 265/40R22+3.08%
- 315/30R22 vs 265/35R22-0.47%
- 315/30R22 vs 285/35R22+1.40%
- 315/30R22 vs 315/35R21+0.82%
- 315/30R22 vs 275/35R22+0.47%
- 315/30R22 vs 295/35R22+2.34%
- 315/30R22 vs 315/35R22+4.21%
- 315/30R22 vs 285/30R22-2.41%
- 315/30R22 vs 295/30R22-1.60%
- 315/30R22 vs 245/45R21+0.82%
Questions
Can I replace 315/30R22 with 275/40R21?
275/40R21 is a safe swap for 315/30R22 by the usual ±3% rule: the diameter differs by +0.75%.
What's the difference between 315/30R22 and 275/40R21?
275/40R21 is 0.22" taller and 40 mm narrower; the sidewall is +0.61". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 275/40R21 fit on 315/30R22 wheels?
No — 315/30R22 needs a 22" wheel and 275/40R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.