Comparison
255/35 R21 vs 255/45 R20
255/45 R20 drops the rim from 21 to 20 inches versus 255/35 R21, trading wheel size for taller sidewall. This tire combination noticeably changes overall diameter compared to OEM.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Minus-sizing keeps replacement costs down and opens up a wider range of winter and all-terrain tires. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/45 R20 is 25.6 mm taller than 255/35 R21, shifting the speedometer by +3.60%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+25.6 mm
3.60%
Speedometer at 100
103.6 km/h
+3.60% error
Ground clearance
+12.8 mm
ride height delta
Sidewall change
+25.5 mm
revs/km: 431.6
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/compare/255-35-r21-vs-255-45-r20Detailed comparison
| Metric | 255/35 R21 | 255/45 R20 | Difference |
|---|---|---|---|
| Overall diameter | 711.9 mm | 737.5 mm | +25.6 mm (+3.60%) |
| Sidewall height | 89.3 mm | 114.8 mm | +25.5 mm |
| Circumference | 2.236 m | 2.317 m | +80.4 mm |
| Revs / km | 447.1 | 431.6 | -15.5 |
| Ground clearance | reference | +12.8 mm | +12.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.6 km/h | +3.60 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 103.6 km/h after switching to 255/45 R20 — a +3.60% 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 +12.8 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
255/45 R20
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