Comparison
255/45 R18 vs 265/40 R18
Stepping from 255/45 R18 to 265/40 R18 keeps the 18-inch wheel but widens the section by 10 mm. This setup moves rolling diameter a touch off the original spec.
Expect a slight but noticeable shift in indicated speed compared to the original tires. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 265/40 R18 is 17.5 mm shorter than 255/45 R18, shifting the speedometer by -2.55%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.5 mm
-2.55%
Speedometer at 100
97.5 km/h
-2.55% error
Ground clearance
-8.8 mm
ride height delta
Sidewall change
-8.8 mm
revs/km: 475.7
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/compare/255-45-r18-vs-265-40-r18Detailed comparison
| Metric | 255/45 R18 | 265/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 686.7 mm | 669.2 mm | -17.5 mm (-2.55%) |
| Sidewall height | 114.8 mm | 106.0 mm | -8.8 mm |
| Circumference | 2.157 m | 2.102 m | -55.0 mm |
| Revs / km | 463.5 | 475.7 | +12.1 |
| Ground clearance | reference | -8.8 mm | -8.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.5 km/h | -2.55 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 -2.55% 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 -8.8 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.
Back to
255/45 R18
Back to
265/40 R18
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