Comparison
215/45 R18 vs 275/40 R18
275/40 R18 is a wider variation of 215/45 R18 on the same 18-inch rim, adding 60 mm of tread footprint. This tire combination swings rolling diameter far enough to feel on the road. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides.
Indicated speed will drift far enough that recalibration is worth considering. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 275/40 R18 is 26.5 mm taller than 215/45 R18, shifting the speedometer by +4.07%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+26.5 mm
4.07%
Speedometer at 100
104.1 km/h
+4.07% error
Ground clearance
+13.3 mm
ride height delta
Sidewall change
+13.3 mm
revs/km: 470.0
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/compare/215-45-r18-vs-275-40-r18Detailed comparison
| Metric | 215/45 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 650.7 mm | 677.2 mm | +26.5 mm (+4.07%) |
| Sidewall height | 96.8 mm | 110.0 mm | +13.3 mm |
| Circumference | 2.044 m | 2.127 m | +83.3 mm |
| Revs / km | 489.2 | 470.0 | -19.1 |
| Ground clearance | reference | +13.3 mm | +13.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.1 km/h | +4.07 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 104.1 km/h after switching to 275/40 R18 — a +4.07% 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 +13.3 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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215/45 R18
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275/40 R18
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