Comparison
255/35 R20 vs 265/40 R18
Going from 255/35 R20 to 265/40 R18 is a minus-2 setup that adds sidewall on a smaller 18-inch wheel. This sizing approach shifts overall diameter slightly from OEM. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. More sidewall typically improves comfort and curb protection, especially on city streets. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 265/40 R18 is 17.3 mm shorter than 255/35 R20, shifting the speedometer by -2.52%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.3 mm
-2.52%
Speedometer at 100
97.5 km/h
-2.52% error
Ground clearance
-8.6 mm
ride height delta
Sidewall change
+16.8 mm
revs/km: 475.7
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/compare/255-35-r20-vs-265-40-r18Detailed comparison
| Metric | 255/35 R20 | 265/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 686.5 mm | 669.2 mm | -17.3 mm (-2.52%) |
| Sidewall height | 89.3 mm | 106.0 mm | +16.8 mm |
| Circumference | 2.157 m | 2.102 m | -54.3 mm |
| Revs / km | 463.7 | 475.7 | +12.0 |
| Ground clearance | reference | -8.6 mm | -8.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.5 km/h | -2.52 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 97.5 km/h after switching to 265/40 R18 — a -2.52% 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 -8.6 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 R20
Back to
265/40 R18
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