Comparison
235/40 R18 vs 275/40 R18
Stepping from 235/40 R18 to 275/40 R18 keeps the 18-inch wheel but widens the section by 40 mm. This sizing approach moves rolling diameter well outside the usual OEM tolerance. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 275/40 R18 is 32.0 mm taller than 235/40 R18, shifting the speedometer by +4.96%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+32.0 mm
4.96%
Speedometer at 100
105.0 km/h
+4.96% error
Ground clearance
+16.0 mm
ride height delta
Sidewall change
+16.0 mm
revs/km: 470.0
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/compare/235-40-r18-vs-275-40-r18Detailed comparison
| Metric | 235/40 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 677.2 mm | +32.0 mm (+4.96%) |
| Sidewall height | 94.0 mm | 110.0 mm | +16.0 mm |
| Circumference | 2.027 m | 2.127 m | +100.5 mm |
| Revs / km | 493.4 | 470.0 | -23.3 |
| Ground clearance | reference | +16.0 mm | +16.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 105.0 km/h | +4.96 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 105.0 km/h after switching to 275/40 R18 — a +4.96% 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 +16.0 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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235/40 R18
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275/40 R18
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