Comparison
225/40 R18 vs 235/40 R18
On the same 18-inch wheel, 235/40 R18 grows the section width by 10 mm versus 225/40 R18. This tire combination barely shifts the rolling circumference. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 235/40 R18 is 8.0 mm taller than 225/40 R18, shifting the speedometer by +1.26%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.0 mm
1.26%
Speedometer at 100
101.3 km/h
+1.26% error
Ground clearance
+4.0 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 493.4
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/compare/225-40-r18-vs-235-40-r18Detailed comparison
| Metric | 225/40 R18 | 235/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 637.2 mm | 645.2 mm | +8.0 mm (+1.26%) |
| Sidewall height | 90.0 mm | 94.0 mm | +4.0 mm |
| Circumference | 2.002 m | 2.027 m | +25.1 mm |
| Revs / km | 499.5 | 493.4 | -6.2 |
| Ground clearance | reference | +4.0 mm | +4.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.3 km/h | +1.26 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 101.3 km/h after switching to 235/40 R18 — a +1.26% 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 +4.0 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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235/40 R18
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