255/45R20 vs 235/45R21 tire size
235/45R21 vs 255/45R20, diameter
+1.0% taller
- Speedometer
- 59.4 mph
- At a true 60 mph
- Diameter
- 29.33 in
- Was 29.04 in
- Revs per mile
- 688
- Was 695
- 3% guideline
- Within
Car built for 255/45R20, now on 235/45R21.
255/45R20 and 235/45R21
| Measure | 255/45R20 | 235/45R21 | Difference |
|---|---|---|---|
| Width, mm | 255 | 235 | -20 |
| Sidewall, % of width | 45 | 45 | 0 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 4.52 | 4.16 | -0.35 |
| Diameter, in | 29.04 | 29.33 | +0.29 (+1.0%) |
| Circumference, in | 91.2 | 92.1 | +0.9 |
| Revs per mile | 695 | 688 | -7 (-1.0%) |
Fitting 235/45R21 instead of 255/45R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
Cars with 255/45R20
Cars with 235/45R21
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