Comparison
255/35 R21 vs 285/30 R20
Switching from 255/35 R21 to 285/30 R20 steps down to a 20-inch wheel — a familiar move for winter and dedicated all-terrain sets. This tire combination swings rolling diameter far enough to feel on the road. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 285/30 R20 is 32.9 mm shorter than 255/35 R21, shifting the speedometer by -4.62%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-32.9 mm
-4.62%
Speedometer at 100
95.4 km/h
-4.62% error
Ground clearance
-16.4 mm
ride height delta
Sidewall change
-3.8 mm
revs/km: 468.8
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/compare/255-35-r21-vs-285-30-r20Detailed comparison
| Metric | 255/35 R21 | 285/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 711.9 mm | 679.0 mm | -32.9 mm (-4.62%) |
| Sidewall height | 89.3 mm | 85.5 mm | -3.8 mm |
| Circumference | 2.236 m | 2.133 m | -103.4 mm |
| Revs / km | 447.1 | 468.8 | +21.7 |
| Ground clearance | reference | -16.4 mm | -16.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.4 km/h | -4.62 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 95.4 km/h after switching to 285/30 R20 — a -4.62% offset. Use the speedometer error calculator to recheck for other indicated speeds, and the speedometer error guide for the full background.
Ground clearance change
The new tire's half-diameter changes ride height by -16.4 mm. Small differences are absorbed by suspension travel, but anything beyond ±10 mm can affect headlight aim, fender clearance and bump-stop margin. See the plus-sizing guide before committing.
Back to
255/35 R21
Back to
285/30 R20
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