235/40R20 vs 305/30R20 tire size
305/30R20 vs 235/40R20, diameter
-0.7% shorter
- Speedometer
- 60.4 mph
- At a true 60 mph
- Diameter
- 27.20 in
- Was 27.40 in
- Revs per mile
- 741
- Was 736
- 3% guideline
- Within
Car built for 235/40R20, now on 305/30R20.
235/40R20 and 305/30R20
| Measure | 235/40R20 | 305/30R20 | Difference |
|---|---|---|---|
| Width, mm | 235 | 305 | +70 |
| Sidewall, % of width | 40 | 30 | -10 |
| Rim, in | 20 | 20 | 0 |
| Section height, in | 3.70 | 3.60 | -0.10 |
| Diameter, in | 27.40 | 27.20 | -0.20 (-0.7%) |
| Circumference, in | 86.1 | 85.5 | -0.6 |
| Revs per mile | 736 | 741 | +5 (+0.7%) |
Fitting 305/30R20 instead of 235/40R20
Within the usual 3% diameter guideline.
- 70 mm wider. Check rubbing at full lock.
Cars with 235/40R20
Cars with 305/30R20
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