Comparison
235/45 R18 vs 275/40 R18
On the same 18-inch wheel, 275/40 R18 grows the section width by 40 mm versus 235/45 R18. This setup preserves rolling diameter within a hair of the original.
Speedometer drift stays small enough that most drivers won't notice it day to day. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. 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.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 275/40 R18 is 8.5 mm taller than 235/45 R18, shifting the speedometer by +1.27%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.5 mm
1.27%
Speedometer at 100
101.3 km/h
+1.27% error
Ground clearance
+4.3 mm
ride height delta
Sidewall change
+4.3 mm
revs/km: 470.0
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/compare/235-45-r18-vs-275-40-r18Detailed comparison
| Metric | 235/45 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 677.2 mm | +8.5 mm (+1.27%) |
| Sidewall height | 105.8 mm | 110.0 mm | +4.3 mm |
| Circumference | 2.101 m | 2.127 m | +26.7 mm |
| Revs / km | 476.0 | 470.0 | -6.0 |
| Ground clearance | reference | +4.3 mm | +4.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.3 km/h | +1.27 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 101.3 km/h after switching to 275/40 R18 — a +1.27% 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 +4.3 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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235/45 R18
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275/40 R18
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