235/50R20 vs 255/40R21 tire size
255/40R21 vs 235/50R20, diameter
-0.8% shorter
- Speedometer
- 60.5 mph
- At a true 60 mph
- Diameter
- 29.03 in
- Was 29.25 in
- Revs per mile
- 695
- Was 689
- 3% guideline
- Within
Car built for 235/50R20, now on 255/40R21.
235/50R20 and 255/40R21
| Measure | 235/50R20 | 255/40R21 | Difference |
|---|---|---|---|
| Width, mm | 235 | 255 | +20 |
| Sidewall, % of width | 50 | 40 | -10 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 4.63 | 4.02 | -0.61 |
| Diameter, in | 29.25 | 29.03 | -0.22 (-0.8%) |
| Circumference, in | 91.9 | 91.2 | -0.7 |
| Revs per mile | 689 | 695 | +5 (+0.8%) |
Fitting 255/40R21 instead of 235/50R20
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 235/50R20
Cars with 255/40R21
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