285/45R20 vs 295/40R21
295/40R21 is a safe swap for 285/45R20 by the usual ±3% rule: the diameter differs by +0.64%.
Speedometer and odometer
With 295/40R21 on a car calibrated for 285/45R20, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.5 mph |
Other sizes close to 285/45R20
- 285/45R20 vs 245/45R20-4.71%
- 285/45R20 vs 255/45R20-3.53%
- 285/45R20 vs 255/50R20-0.20%
- 285/45R20 vs 275/40R20-4.77%
- 285/45R20 vs 265/50R20+1.11%
- 285/45R20 vs 245/50R20-1.50%
- 285/45R20 vs 275/45R20-1.18%
- 285/45R20 vs 255/55R20+3.14%
- 285/45R20 vs 235/55R20+0.26%
- 285/45R20 vs 265/45R20-2.35%
- 285/45R20 vs 255/55R19-0.18%
- 285/45R20 vs 315/35R20-4.71%
Questions
Can I replace 285/45R20 with 295/40R21?
295/40R21 is a safe swap for 285/45R20 by the usual ±3% rule: the diameter differs by +0.64%.
What's the difference between 285/45R20 and 295/40R21?
295/40R21 is 0.19" taller and 10 mm wider; the sidewall is -0.40". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 295/40R21 fit on 285/45R20 wheels?
No — 285/45R20 needs a 20" wheel and 295/40R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.