255/50R20 vs 295/40R21
295/40R21 is a safe swap for 255/50R20 by the usual ±3% rule: the diameter differs by +0.84%.
Speedometer and odometer
With 295/40R21 on a car calibrated for 255/50R20, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.7 mph |
Other sizes close to 255/50R20
- 255/50R20 vs 245/45R20-4.52%
- 255/50R20 vs 255/45R20-3.34%
- 255/50R20 vs 275/40R20-4.59%
- 255/50R20 vs 265/50R20+1.31%
- 255/50R20 vs 245/50R20-1.31%
- 255/50R20 vs 275/45R20-0.98%
- 255/50R20 vs 255/55R20+3.34%
- 255/50R20 vs 235/55R20+0.46%
- 255/50R20 vs 265/45R20-2.16%
- 255/50R20 vs 255/55R19+0.01%
- 255/50R20 vs 315/35R20-4.52%
- 255/50R20 vs 275/50R20+2.62%
Questions
Can I replace 255/50R20 with 295/40R21?
295/40R21 is a safe swap for 255/50R20 by the usual ±3% rule: the diameter differs by +0.84%.
What's the difference between 255/50R20 and 295/40R21?
295/40R21 is 0.25" taller and 40 mm wider; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 295/40R21 fit on 255/50R20 wheels?
No — 255/50R20 needs a 20" wheel and 295/40R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.