255/50R18 vs 315/40R18 tire size
315/40R18 vs 255/50R18, diameter
-0.4% shorter
- Speedometer
- 60.3 mph
- At a true 60 mph
- Diameter
- 27.92 in
- Was 28.04 in
- Revs per mile
- 722
- Was 719
- 3% guideline
- Within
Car built for 255/50R18, now on 315/40R18.
255/50R18 and 315/40R18
| Measure | 255/50R18 | 315/40R18 | Difference |
|---|---|---|---|
| Width, mm | 255 | 315 | +60 |
| Sidewall, % of width | 50 | 40 | -10 |
| Rim, in | 18 | 18 | 0 |
| Section height, in | 5.02 | 4.96 | -0.06 |
| Diameter, in | 28.04 | 27.92 | -0.12 (-0.4%) |
| Circumference, in | 88.1 | 87.7 | -0.4 |
| Revs per mile | 719 | 722 | +3 (+0.4%) |
Fitting 315/40R18 instead of 255/50R18
Within the usual 3% diameter guideline.
- 60 mm wider. Check rubbing at full lock.
Cars with 315/40R18
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