235/55R20 vs 255/45R21 tire size
255/45R21 vs 235/55R20, diameter
-0.5% shorter
- Speedometer
- 60.3 mph
- At a true 60 mph
- Diameter
- 30.04 in
- Was 30.18 in
- Revs per mile
- 671
- Was 668
- 3% guideline
- Within
Car built for 235/55R20, now on 255/45R21.
235/55R20 and 255/45R21
| Measure | 235/55R20 | 255/45R21 | Difference |
|---|---|---|---|
| Width, mm | 235 | 255 | +20 |
| Sidewall, % of width | 55 | 45 | -10 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 5.09 | 4.52 | -0.57 |
| Diameter, in | 30.18 | 30.04 | -0.14 (-0.5%) |
| Circumference, in | 94.8 | 94.4 | -0.4 |
| Revs per mile | 668 | 671 | +3 (+0.5%) |
Fitting 255/45R21 instead of 235/55R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
- 20 mm wider. Check rubbing at full lock.
- Shorter sidewall: 0.6 in less.
Cars with 235/55R20
Cars with 255/45R21
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