Comparison
255/55 R18 vs 265/40 R20
Plus-sizing from 255/55 R18 to 265/40 R20 keeps overall diameter close to factory while opening room for a larger 20-inch wheel. This swap moves rolling diameter a touch off the original spec. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 265/40 R20 is 17.7 mm shorter than 255/55 R18, shifting the speedometer by -2.40%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.7 mm
-2.40%
Speedometer at 100
97.6 km/h
-2.40% error
Ground clearance
-8.9 mm
ride height delta
Sidewall change
-34.3 mm
revs/km: 442.1
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/compare/255-55-r18-vs-265-40-r20Detailed comparison
| Metric | 255/55 R18 | 265/40 R20 | Difference |
|---|---|---|---|
| Overall diameter | 737.7 mm | 720.0 mm | -17.7 mm (-2.40%) |
| Sidewall height | 140.3 mm | 106.0 mm | -34.3 mm |
| Circumference | 2.318 m | 2.262 m | -55.6 mm |
| Revs / km | 431.5 | 442.1 | +10.6 |
| Ground clearance | reference | -8.9 mm | -8.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.6 km/h | -2.40 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 97.6 km/h after switching to 265/40 R20 — a -2.40% 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 -8.9 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
255/55 R18
Back to
265/40 R20
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