Comparison
215/45 R18 vs 245/40 R17
Going from 215/45 R18 to 245/40 R17 is a minus-1 setup that adds sidewall on a smaller 17-inch wheel. This alternative fitment 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. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. The smaller wheel is also lighter and easier to find affordable winter rubber for. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 245/40 R17 is 22.9 mm shorter than 215/45 R18, shifting the speedometer by -3.52%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-22.9 mm
-3.52%
Speedometer at 100
96.5 km/h
-3.52% error
Ground clearance
-11.5 mm
ride height delta
Sidewall change
+1.3 mm
revs/km: 507.0
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/compare/215-45-r18-vs-245-40-r17Detailed comparison
| Metric | 215/45 R18 | 245/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 650.7 mm | 627.8 mm | -22.9 mm (-3.52%) |
| Sidewall height | 96.8 mm | 98.0 mm | +1.3 mm |
| Circumference | 2.044 m | 1.972 m | -71.9 mm |
| Revs / km | 489.2 | 507.0 | +17.8 |
| Ground clearance | reference | -11.5 mm | -11.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.5 km/h | -3.52 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 96.5 km/h after switching to 245/40 R17 — a -3.52% 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 -11.5 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
215/45 R18
Back to
245/40 R17
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