Comparison
235/40 R18 vs 255/35 R18
On the same 18-inch wheel, 255/35 R18 grows the section width by 20 mm versus 235/40 R18. This wheel and tire pairing barely shifts the rolling circumference. Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. 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.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 255/35 R18 is 9.5 mm shorter than 235/40 R18, shifting the speedometer by -1.47%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-9.5 mm
-1.47%
Speedometer at 100
98.5 km/h
-1.47% error
Ground clearance
-4.8 mm
ride height delta
Sidewall change
-4.8 mm
revs/km: 500.7
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/compare/235-40-r18-vs-255-35-r18Detailed comparison
| Metric | 235/40 R18 | 255/35 R18 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 635.7 mm | -9.5 mm (-1.47%) |
| Sidewall height | 94.0 mm | 89.3 mm | -4.8 mm |
| Circumference | 2.027 m | 1.997 m | -29.8 mm |
| Revs / km | 493.4 | 500.7 | +7.4 |
| Ground clearance | reference | -4.8 mm | -4.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.5 km/h | -1.47 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 98.5 km/h after switching to 255/35 R18 — a -1.47% 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 -4.8 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.
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235/40 R18
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255/35 R18
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