255/50R20 vs 285/40R21 tire size
285/40R21 vs 255/50R20, diameter
-0.2% shorter
- Speedometer
- 60.1 mph
- At a true 60 mph
- Diameter
- 29.98 in
- Was 30.04 in
- Revs per mile
- 673
- Was 671
- 3% guideline
- Within
Car built for 255/50R20, now on 285/40R21.
255/50R20 and 285/40R21
| Measure | 255/50R20 | 285/40R21 | Difference |
|---|---|---|---|
| Width, mm | 255 | 285 | +30 |
| Sidewall, % of width | 50 | 40 | -10 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 5.02 | 4.49 | -0.53 |
| Diameter, in | 30.04 | 29.98 | -0.06 (-0.2%) |
| Circumference, in | 94.4 | 94.2 | -0.2 |
| Revs per mile | 671 | 673 | +1 (+0.2%) |
Fitting 285/40R21 instead of 255/50R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
- 30 mm wider. Check rubbing at full lock.
- Shorter sidewall: 0.5 in less.
Cars with 255/50R20
Cars with 285/40R21
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