255/45R20 vs 295/35R21
295/35R21 is a safe swap for 255/45R20 by the usual ±3% rule: the diameter differs by +0.33%.
Speedometer and odometer
With 295/35R21 on a car calibrated for 255/45R20, 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 | 45.1 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.3 mph |
Other sizes close to 255/45R20
- 255/45R20 vs 235/55R19+0.49%
- 255/45R20 vs 245/45R20-1.22%
- 255/45R20 vs 255/50R19+0.01%
- 255/45R20 vs 275/40R20-1.29%
- 255/45R20 vs 255/50R20+3.46%
- 255/45R20 vs 245/40R20-4.54%
- 255/45R20 vs 265/50R20+4.81%
- 255/45R20 vs 245/50R20+2.10%
- 255/45R20 vs 275/45R20+2.44%
- 255/45R20 vs 235/55R20+3.93%
- 255/45R20 vs 255/40R20-3.46%
- 255/45R20 vs 265/45R20+1.22%
Questions
Can I replace 255/45R20 with 295/35R21?
295/35R21 is a safe swap for 255/45R20 by the usual ±3% rule: the diameter differs by +0.33%.
What's the difference between 255/45R20 and 295/35R21?
295/35R21 is 0.09" taller and 40 mm wider; the sidewall is -0.45". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 295/35R21 fit on 255/45R20 wheels?
No — 255/45R20 needs a 20" wheel and 295/35R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.