245/50R20 vs 275/40R21
275/40R21 is a safe swap for 245/50R20 by the usual ±3% rule: the diameter differs by +0.05%.
Speedometer and odometer
With 275/40R21 on a car calibrated for 245/50R20, the speedometer reads 60.0 mph when you're really doing 60, and the odometer under-counts by 0.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.0 mph |
| 45 mph | 45.0 mph |
| 60 mph | 60.0 mph |
| 70 mph | 70.0 mph |
| 80 mph | 80.0 mph |
Other sizes close to 245/50R20
- 245/50R20 vs 245/45R20-3.25%
- 245/50R20 vs 255/45R20-2.06%
- 245/50R20 vs 255/50R20+1.33%
- 245/50R20 vs 275/40R20-3.32%
- 245/50R20 vs 265/50R20+2.66%
- 245/50R20 vs 275/45R20+0.33%
- 245/50R20 vs 255/55R20+4.71%
- 245/50R20 vs 235/55R20+1.79%
- 245/50R20 vs 245/55R19-0.12%
- 245/50R20 vs 265/45R20-0.86%
- 245/50R20 vs 265/50R19-0.72%
- 245/50R20 vs 315/35R20-3.25%
Questions
Can I replace 245/50R20 with 275/40R21?
275/40R21 is a safe swap for 245/50R20 by the usual ±3% rule: the diameter differs by +0.05%.
What's the difference between 245/50R20 and 275/40R21?
275/40R21 is 0.02" taller and 30 mm wider; the sidewall is -0.49". At an indicated 60 mph you'd actually be doing 60.0 mph.
Will 275/40R21 fit on 245/50R20 wheels?
No — 245/50R20 needs a 20" wheel and 275/40R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.