Comparison
215/55 R17 vs 235/40 R18
Switching from 215/55 R17 to 235/40 R18 is a plus-1 upgrade that wraps a shorter sidewall around a larger 18-inch wheel. This tire combination swings rolling diameter far enough to feel on the road.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Visually, the bigger wheel fills the arch and gives the car a more aggressive stance. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 235/40 R18 is 23.1 mm shorter than 215/55 R17, shifting the speedometer by -3.46%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-23.1 mm
-3.46%
Speedometer at 100
96.5 km/h
-3.46% error
Ground clearance
-11.5 mm
ride height delta
Sidewall change
-24.3 mm
revs/km: 493.4
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/compare/215-55-r17-vs-235-40-r18Detailed comparison
| Metric | 215/55 R17 | 235/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 668.3 mm | 645.2 mm | -23.1 mm (-3.46%) |
| Sidewall height | 118.3 mm | 94.0 mm | -24.3 mm |
| Circumference | 2.100 m | 2.027 m | -72.6 mm |
| Revs / km | 476.3 | 493.4 | +17.1 |
| Ground clearance | reference | -11.5 mm | -11.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.5 km/h | -3.46 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 96.5 km/h after switching to 235/40 R18 — a -3.46% 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 -11.5 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.
Back to
215/55 R17
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235/40 R18
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