Comparison
225/55 R16 vs 235/40 R18
Going from 225/55 R16 to 235/40 R18 steps up to a 18-inch rim while trimming sidewall to stay near OEM rolling diameter. This tire combination lands within OEM rolling-diameter tolerance. Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. 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 8.7 mm shorter than 225/55 R16, shifting the speedometer by -1.33%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-8.7 mm
-1.33%
Speedometer at 100
98.7 km/h
-1.33% error
Ground clearance
-4.3 mm
ride height delta
Sidewall change
-29.8 mm
revs/km: 493.4
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/compare/225-55-r16-vs-235-40-r18Detailed comparison
| Metric | 225/55 R16 | 235/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 653.9 mm | 645.2 mm | -8.7 mm (-1.33%) |
| Sidewall height | 123.8 mm | 94.0 mm | -29.8 mm |
| Circumference | 2.054 m | 2.027 m | -27.3 mm |
| Revs / km | 486.8 | 493.4 | +6.6 |
| Ground clearance | reference | -4.3 mm | -4.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.7 km/h | -1.33 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 98.7 km/h after switching to 235/40 R18 — a -1.33% 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 -4.3 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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225/55 R16
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235/40 R18
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