Comparison
245/40 R17 vs 245/40 R18
Plus-sizing from 245/40 R17 to 245/40 R18 keeps overall diameter close to factory while opening room for a larger 18-inch wheel. This setup swings rolling diameter far enough to feel on the road. Visually, the bigger wheel fills the arch and gives the car a more aggressive stance.
Indicated speed will drift far enough that recalibration is worth considering. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 245/40 R18 is 25.4 mm taller than 245/40 R17, shifting the speedometer by +4.05%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+25.4 mm
4.05%
Speedometer at 100
104.0 km/h
+4.05% error
Ground clearance
+12.7 mm
ride height delta
Sidewall change
0.0 mm
revs/km: 487.3
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/compare/245-40-r17-vs-245-40-r18Detailed comparison
| Metric | 245/40 R17 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 627.8 mm | 653.2 mm | +25.4 mm (+4.05%) |
| Sidewall height | 98.0 mm | 98.0 mm | 0.0 mm |
| Circumference | 1.972 m | 2.052 m | +79.8 mm |
| Revs / km | 507.0 | 487.3 | -19.7 |
| Ground clearance | reference | +12.7 mm | +12.7 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.0 km/h | +4.05 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 104.0 km/h after switching to 245/40 R18 — a +4.05% 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 +12.7 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 R17
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245/40 R18
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