Comparison
245/40 R18 vs 275/40 R18
275/40 R18 is a wider variation of 245/40 R18 on the same 18-inch rim, adding 30 mm of tread footprint. This setup swings rolling diameter far enough to feel on the road.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 275/40 R18 is 24.0 mm taller than 245/40 R18, shifting the speedometer by +3.67%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+24.0 mm
3.67%
Speedometer at 100
103.7 km/h
+3.67% error
Ground clearance
+12.0 mm
ride height delta
Sidewall change
+12.0 mm
revs/km: 470.0
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/compare/245-40-r18-vs-275-40-r18Detailed comparison
| Metric | 245/40 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 653.2 mm | 677.2 mm | +24.0 mm (+3.67%) |
| Sidewall height | 98.0 mm | 110.0 mm | +12.0 mm |
| Circumference | 2.052 m | 2.127 m | +75.4 mm |
| Revs / km | 487.3 | 470.0 | -17.3 |
| Ground clearance | reference | +12.0 mm | +12.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.7 km/h | +3.67 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 103.7 km/h after switching to 275/40 R18 — a +3.67% 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 +12.0 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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245/40 R18
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275/40 R18
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