255/45R20 vs 255/40R21 tire size
255/40R21 vs 255/45R20, diameter
Same diameter
- Speedometer
- 60.0 mph
- At a true 60 mph
- Diameter
- 29.03 in
- Was 29.04 in
- Revs per mile
- 695
- Was 695
- 3% guideline
- Within
Car built for 255/45R20, now on 255/40R21.
255/45R20 and 255/40R21
| Measure | 255/45R20 | 255/40R21 | Difference |
|---|---|---|---|
| Width, mm | 255 | 255 | 0 |
| Sidewall, % of width | 45 | 40 | -5 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 4.52 | 4.02 | -0.50 |
| Diameter, in | 29.04 | 29.03 | 0 (-0.0%) |
| Circumference, in | 91.2 | 91.2 | -0.0 |
| Revs per mile | 695 | 695 | +0 (+0.0%) |
Fitting 255/40R21 instead of 255/45R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
- Shorter sidewall: 0.5 in less.
Cars with 255/45R20
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