Comparison
255/45 R18 vs 275/40 R18
On the same 18-inch wheel, 275/40 R18 grows the section width by 20 mm versus 255/45 R18. This alternative fitment keeps overall diameter very close to stock. Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 275/40 R18 is 9.5 mm shorter than 255/45 R18, shifting the speedometer by -1.38%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-9.5 mm
-1.38%
Speedometer at 100
98.6 km/h
-1.38% error
Ground clearance
-4.8 mm
ride height delta
Sidewall change
-4.8 mm
revs/km: 470.0
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/compare/255-45-r18-vs-275-40-r18Detailed comparison
| Metric | 255/45 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 686.7 mm | 677.2 mm | -9.5 mm (-1.38%) |
| Sidewall height | 114.8 mm | 110.0 mm | -4.8 mm |
| Circumference | 2.157 m | 2.127 m | -29.8 mm |
| Revs / km | 463.5 | 470.0 | +6.5 |
| Ground clearance | reference | -4.8 mm | -4.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.6 km/h | -1.38 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 98.6 km/h after switching to 275/40 R18 — a -1.38% 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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255/45 R18
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275/40 R18
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225/50 R18 vs 275/40 R18
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235/50 R18 vs 255/45 R18
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245/45 R18 vs 255/45 R18
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235/50 R18 vs 275/40 R18
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