265/40R20 vs 315/30R21
315/30R21 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +0.33%.
Speedometer and odometer
With 315/30R21 on a car calibrated for 265/40R20, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.3 mph |
Other sizes close to 265/40R20
- 265/40R20 vs 245/45R20+1.18%
- 265/40R20 vs 255/45R20+2.43%
- 265/40R20 vs 275/40R20+1.11%
- 265/40R20 vs 245/40R20-2.22%
- 265/40R20 vs 245/50R20+4.58%
- 265/40R20 vs 275/45R20+4.93%
- 265/40R20 vs 255/35R20-4.65%
- 265/40R20 vs 255/40R20-1.11%
- 265/40R20 vs 275/35R20-2.71%
- 265/40R20 vs 235/50R19-0.33%
- 265/40R20 vs 265/45R20+3.68%
- 265/40R20 vs 285/35R20-1.74%
Questions
Can I replace 265/40R20 with 315/30R21?
315/30R21 is a safe swap for 265/40R20 by the usual ±3% rule: the diameter differs by +0.33%.
What's the difference between 265/40R20 and 315/30R21?
315/30R21 is 0.09" taller and 50 mm wider; the sidewall is -0.45". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 315/30R21 fit on 265/40R20 wheels?
No — 265/40R20 needs a 20" wheel and 315/30R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.