Comparison
245/45 R17 vs 275/40 R18
Going from 245/45 R17 to 275/40 R18 steps up to a 18-inch rim while trimming sidewall to stay near OEM rolling diameter. This swap moves rolling diameter well outside the usual OEM tolerance.
Indicated speed will drift far enough that recalibration is worth considering. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. The larger wheel shows more of the brake hardware and tightens up the wheel-gap look. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 275/40 R18 is 24.9 mm taller than 245/45 R17, shifting the speedometer by +3.82%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+24.9 mm
3.82%
Speedometer at 100
103.8 km/h
+3.82% error
Ground clearance
+12.5 mm
ride height delta
Sidewall change
-0.3 mm
revs/km: 470.0
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/compare/245-45-r17-vs-275-40-r18Detailed comparison
| Metric | 245/45 R17 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 652.3 mm | 677.2 mm | +24.9 mm (+3.82%) |
| Sidewall height | 110.3 mm | 110.0 mm | -0.3 mm |
| Circumference | 2.049 m | 2.127 m | +78.2 mm |
| Revs / km | 488.0 | 470.0 | -17.9 |
| Ground clearance | reference | +12.5 mm | +12.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.8 km/h | +3.82 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 103.8 km/h after switching to 275/40 R18 — a +3.82% 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 +12.5 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.
Back to
245/45 R17
Back to
275/40 R18
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