Comparison
225/40 R18 vs 235/45 R17
235/45 R17 drops the rim from 18 to 17 inches versus 225/40 R18, trading wheel size for taller sidewall. This swap preserves rolling diameter within a hair of the original. The speedometer offset is mild and well inside what most cars can tolerate without recalibration. More sidewall typically improves comfort and curb protection, especially on city streets. 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: 235/45 R17 is 6.1 mm taller than 225/40 R18, shifting the speedometer by +0.96%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+6.1 mm
0.96%
Speedometer at 100
101.0 km/h
+0.96% error
Ground clearance
+3.0 mm
ride height delta
Sidewall change
+15.8 mm
revs/km: 494.8
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/compare/225-40-r18-vs-235-45-r17Detailed comparison
| Metric | 225/40 R18 | 235/45 R17 | Difference |
|---|---|---|---|
| Overall diameter | 637.2 mm | 643.3 mm | +6.1 mm (+0.96%) |
| Sidewall height | 90.0 mm | 105.8 mm | +15.8 mm |
| Circumference | 2.002 m | 2.021 m | +19.2 mm |
| Revs / km | 499.5 | 494.8 | -4.7 |
| Ground clearance | reference | +3.0 mm | +3.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.0 km/h | +0.96 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 101.0 km/h after switching to 235/45 R17 — a +0.96% 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 +3.0 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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225/40 R18
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235/45 R17
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