245/45R20 vs 285/35R21
285/35R21 is a safe swap for 245/45R20 by the usual ±3% rule: the diameter differs by +0.60%.
Speedometer and odometer
With 285/35R21 on a car calibrated for 245/45R20, 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 245/45R20
- 245/45R20 vs 255/45R20+1.24%
- 245/45R20 vs 275/40R20-0.07%
- 245/45R20 vs 255/50R20+4.74%
- 245/45R20 vs 245/40R20-3.36%
- 245/45R20 vs 245/50R20+3.36%
- 245/45R20 vs 275/45R20+3.71%
- 245/45R20 vs 225/55R19+0.22%
- 245/45R20 vs 255/40R20-2.26%
- 245/45R20 vs 275/35R20-3.84%
- 245/45R20 vs 265/45R20+2.47%
- 245/45R20 vs 285/35R20-2.88%
- 245/45R20 vs 315/35R200.00%
Questions
Can I replace 245/45R20 with 285/35R21?
285/35R21 is a safe swap for 245/45R20 by the usual ±3% rule: the diameter differs by +0.60%.
What's the difference between 245/45R20 and 285/35R21?
285/35R21 is 0.17" taller and 40 mm wider; the sidewall is -0.41". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 285/35R21 fit on 245/45R20 wheels?
No — 245/45R20 needs a 20" wheel and 285/35R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.