Comparison
225/50 R17 vs 235/40 R18
Switching from 225/50 R17 to 235/40 R18 is a plus-1 upgrade that wraps a shorter sidewall around a larger 18-inch wheel. This wheel and tire pairing trims or stretches rolling diameter by a small margin. Expect a slight but noticeable shift in indicated speed compared to the original tires. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 235/40 R18 is 11.6 mm shorter than 225/50 R17, shifting the speedometer by -1.77%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-11.6 mm
-1.77%
Speedometer at 100
98.2 km/h
-1.77% error
Ground clearance
-5.8 mm
ride height delta
Sidewall change
-18.5 mm
revs/km: 493.4
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/compare/225-50-r17-vs-235-40-r18Detailed comparison
| Metric | 225/50 R17 | 235/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 656.8 mm | 645.2 mm | -11.6 mm (-1.77%) |
| Sidewall height | 112.5 mm | 94.0 mm | -18.5 mm |
| Circumference | 2.063 m | 2.027 m | -36.4 mm |
| Revs / km | 484.6 | 493.4 | +8.7 |
| Ground clearance | reference | -5.8 mm | -5.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.2 km/h | -1.77 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 98.2 km/h after switching to 235/40 R18 — a -1.77% 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 -5.8 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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225/50 R17
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235/40 R18
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