235/50R17 vs 255/40R18 tire size
255/40R18 vs 235/50R17, diameter
-0.8% shorter
- Speedometer
- 60.5 mph
- At a true 60 mph
- Diameter
- 26.03 in
- Was 26.25 in
- Revs per mile
- 775
- Was 768
- 3% guideline
- Within
Car built for 235/50R17, now on 255/40R18.
235/50R17 and 255/40R18
| Measure | 235/50R17 | 255/40R18 | Difference |
|---|---|---|---|
| Width, mm | 235 | 255 | +20 |
| Sidewall, % of width | 50 | 40 | -10 |
| Rim, in | 17 | 18 | +1 |
| Section height, in | 4.63 | 4.02 | -0.61 |
| Diameter, in | 26.25 | 26.03 | -0.22 (-0.8%) |
| Circumference, in | 82.5 | 81.8 | -0.7 |
| Revs per mile | 768 | 775 | +7 (+0.8%) |
Fitting 255/40R18 instead of 235/50R17
Within the usual 3% diameter guideline.
- Needs 18 in wheels.
- 20 mm wider. Check rubbing at full lock.
- Shorter sidewall: 0.6 in less.
Cars with 235/50R17
Cars with 255/40R18
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