Comparison
255/40 R18 vs 265/40 R18
On the same 18-inch wheel, 265/40 R18 grows the section width by 10 mm versus 255/40 R18. This swap lands within OEM rolling-diameter tolerance. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff.
The speedometer offset is mild and well inside what most cars can tolerate without recalibration. 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: 265/40 R18 is 8.0 mm taller than 255/40 R18, shifting the speedometer by +1.21%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.0 mm
1.21%
Speedometer at 100
101.2 km/h
+1.21% error
Ground clearance
+4.0 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 475.7
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/compare/255-40-r18-vs-265-40-r18Detailed comparison
| Metric | 255/40 R18 | 265/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 661.2 mm | 669.2 mm | +8.0 mm (+1.21%) |
| Sidewall height | 102.0 mm | 106.0 mm | +4.0 mm |
| Circumference | 2.077 m | 2.102 m | +25.1 mm |
| Revs / km | 481.4 | 475.7 | -5.8 |
| Ground clearance | reference | +4.0 mm | +4.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.2 km/h | +1.21 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 101.2 km/h after switching to 265/40 R18 — a +1.21% 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 +4.0 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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255/40 R18
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265/40 R18
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