265/45R21 vs 315/40R21
315/40R21 is a safe swap for 265/45R21 by the usual ±3% rule: the diameter differs by +1.75%.
Speedometer and odometer
With 315/40R21 on a car calibrated for 265/45R21, the speedometer reads 59.0 mph when you're really doing 60, and the odometer under-counts by 1.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.5 mph |
| 45 mph | 45.8 mph |
| 60 mph | 61.0 mph |
| 70 mph | 71.2 mph |
| 80 mph | 81.4 mph |
Other sizes close to 265/45R21
- 265/45R21 vs 265/50R20+0.14%
- 265/45R21 vs 235/55R20-0.70%
- 265/45R21 vs 265/40R21-3.43%
- 265/45R21 vs 295/35R21-4.15%
- 265/45R21 vs 275/40R22+0.89%
- 265/45R21 vs 275/45R21+1.17%
- 265/45R21 vs 265/40R22-0.14%
- 265/45R21 vs 255/40R21-4.47%
- 265/45R21 vs 295/40R21-0.32%
- 265/45R21 vs 285/45R21+2.33%
- 265/45R21 vs 285/40R21-1.36%
- 265/45R21 vs 275/40R21-2.40%
Questions
Can I replace 265/45R21 with 315/40R21?
315/40R21 is a safe swap for 265/45R21 by the usual ±3% rule: the diameter differs by +1.75%.
What's the difference between 265/45R21 and 315/40R21?
315/40R21 is 0.53" taller and 50 mm wider; the sidewall is +0.27". At an indicated 60 mph you'd actually be doing 61.0 mph.
Will 315/40R21 fit on 265/45R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.