325/35R20 vs 285/35R21 tire size
285/35R21 vs 325/35R20, diameter
-0.4% shorter
- Speedometer
- 60.2 mph
- At a true 60 mph
- Diameter
- 28.85 in
- Was 28.96 in
- Revs per mile
- 699
- Was 696
- 3% guideline
- Within
Car built for 325/35R20, now on 285/35R21.
325/35R20 and 285/35R21
| Measure | 325/35R20 | 285/35R21 | Difference |
|---|---|---|---|
| Width, mm | 325 | 285 | -40 |
| Sidewall, % of width | 35 | 35 | 0 |
| Rim, in | 20 | 21 | +1 |
| Section height, in | 4.48 | 3.93 | -0.55 |
| Diameter, in | 28.96 | 28.85 | -0.10 (-0.4%) |
| Circumference, in | 91.0 | 90.6 | -0.3 |
| Revs per mile | 696 | 699 | +2 (+0.4%) |
Fitting 285/35R21 instead of 325/35R20
Within the usual 3% diameter guideline.
- Needs 21 in wheels.
- Shorter sidewall: 0.6 in less.
Cars with 325/35R20
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