255/55R20 vs 285/45R21 tire size
285/45R21 vs 255/55R20, diameter
+0.2% taller
- Speedometer
- 59.9 mph
- At a true 60 mph
- Diameter
- 31.10 in
- Was 31.04 in
- Revs per mile
- 649
- Was 650
- 3% guideline
- Within
Car built for 255/55R20, now on 285/45R21.
255/55R20 and 285/45R21
| Measure | 255/55R20 | 285/45R21 | Difference |
|---|---|---|---|
| Width, mm | 255 | 285 | +30 |
| Sidewall, % of width | 55 | 45 | -10 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 5.52 | 5.05 | -0.47 |
| Diameter, in | 31.04 | 31.10 | +0.06 (+0.2%) |
| Circumference, in | 97.5 | 97.7 | +0.2 |
| Revs per mile | 650 | 649 | -1 (-0.2%) |
Fitting 285/45R21 instead of 255/55R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
- 30 mm wider. Check rubbing at full lock.
Cars with 255/55R20
Cars with 285/45R21
What this cannot tell you
Diameter within 3% is a common shop guideline, not a maker spec.
Load index, offset and clearance are not in this data.
- Two or more sources agree
- One source
- Model-level or estimate
- Sources differ