Comparison
225/40 R18 vs 245/40 R17
Going from 225/40 R18 to 245/40 R17 is a minus-1 setup that adds sidewall on a smaller 17-inch wheel. This setup preserves rolling diameter within a hair of the original.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. Minus-sizing keeps replacement costs down and opens up a wider range of winter and all-terrain tires. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 245/40 R17 is 9.4 mm shorter than 225/40 R18, shifting the speedometer by -1.48%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-9.4 mm
-1.48%
Speedometer at 100
98.5 km/h
-1.48% error
Ground clearance
-4.7 mm
ride height delta
Sidewall change
+8.0 mm
revs/km: 507.0
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/compare/225-40-r18-vs-245-40-r17Detailed comparison
| Metric | 225/40 R18 | 245/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 637.2 mm | 627.8 mm | -9.4 mm (-1.48%) |
| Sidewall height | 90.0 mm | 98.0 mm | +8.0 mm |
| Circumference | 2.002 m | 1.972 m | -29.5 mm |
| Revs / km | 499.5 | 507.0 | +7.5 |
| Ground clearance | reference | -4.7 mm | -4.7 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.5 km/h | -1.48 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 98.5 km/h after switching to 245/40 R17 — a -1.48% 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 -4.7 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.
Back to
225/40 R18
Back to
245/40 R17
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