Comparison
225/55 R17 vs 245/40 R18
Switching from 225/55 R17 to 245/40 R18 is a plus-1 upgrade that wraps a shorter sidewall around a larger 18-inch wheel. This sizing approach moves rolling diameter well outside the usual OEM tolerance. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input.
Indicated speed will drift far enough that recalibration is worth considering. 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: 245/40 R18 is 26.1 mm shorter than 225/55 R17, shifting the speedometer by -3.84%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-26.1 mm
-3.84%
Speedometer at 100
96.2 km/h
-3.84% error
Ground clearance
-13.0 mm
ride height delta
Sidewall change
-25.8 mm
revs/km: 487.3
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/compare/225-55-r17-vs-245-40-r18Detailed comparison
| Metric | 225/55 R17 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 679.3 mm | 653.2 mm | -26.1 mm (-3.84%) |
| Sidewall height | 123.8 mm | 98.0 mm | -25.8 mm |
| Circumference | 2.134 m | 2.052 m | -82.0 mm |
| Revs / km | 468.6 | 487.3 | +18.7 |
| Ground clearance | reference | -13.0 mm | -13.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.2 km/h | -3.84 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 96.2 km/h after switching to 245/40 R18 — a -3.84% 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 -13.0 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.
Back to
225/55 R17
Back to
245/40 R18
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