Comparison
235/40 R18 vs 245/45 R17
245/45 R17 drops the rim from 18 to 17 inches versus 235/40 R18, trading wheel size for taller sidewall. This alternative fitment barely shifts the rolling circumference. Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Extra sidewall absorbs impacts more readily — a sensible bias for daily commuting and broken pavement. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 245/45 R17 is 7.1 mm taller than 235/40 R18, shifting the speedometer by +1.10%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+7.1 mm
1.10%
Speedometer at 100
101.1 km/h
+1.10% error
Ground clearance
+3.5 mm
ride height delta
Sidewall change
+16.3 mm
revs/km: 488.0
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/compare/235-40-r18-vs-245-45-r17Detailed comparison
| Metric | 235/40 R18 | 245/45 R17 | Difference |
|---|---|---|---|
| Overall diameter | 645.2 mm | 652.3 mm | +7.1 mm (+1.10%) |
| Sidewall height | 94.0 mm | 110.3 mm | +16.3 mm |
| Circumference | 2.027 m | 2.049 m | +22.3 mm |
| Revs / km | 493.4 | 488.0 | -5.4 |
| Ground clearance | reference | +3.5 mm | +3.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.1 km/h | +1.10 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 101.1 km/h after switching to 245/45 R17 — a +1.10% 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 +3.5 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.
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235/40 R18
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245/45 R17
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