Comparison
255/35 R21 vs 295/40 R20
Switching from 255/35 R21 to 295/40 R20 steps down to a 20-inch wheel — a familiar move for winter and dedicated all-terrain sets. This swap moves rolling diameter well outside the usual OEM tolerance. More sidewall typically improves comfort and curb protection, especially on city streets.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 295/40 R20 is 32.1 mm taller than 255/35 R21, shifting the speedometer by +4.51%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+32.1 mm
4.51%
Speedometer at 100
104.5 km/h
+4.51% error
Ground clearance
+16.1 mm
ride height delta
Sidewall change
+28.8 mm
revs/km: 427.8
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/compare/255-35-r21-vs-295-40-r20Detailed comparison
| Metric | 255/35 R21 | 295/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 711.9 mm | 744.0 mm | +32.1 mm (+4.51%) |
| Sidewall height | 89.3 mm | 118.0 mm | +28.8 mm |
| Circumference | 2.236 m | 2.337 m | +100.8 mm |
| Revs / km | 447.1 | 427.8 | -19.3 |
| Ground clearance | reference | +16.1 mm | +16.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.5 km/h | +4.51 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 104.5 km/h after switching to 295/40 R20 — a +4.51% 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 +16.1 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.
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255/35 R21
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295/40 R20
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