Comparison
225/50 R18 vs 245/40 R18
Switching from 225/50 R18 to 245/40 R18 drops the aspect ratio by 10 points on the same 18-inch wheel. This setup noticeably changes overall diameter compared to OEM. Indicated speed will drift far enough that recalibration is worth considering. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakeSuits drivers who value sharper steering and appearance over outright ride softness.
Quick math: 245/40 R18 is 29.0 mm shorter than 225/50 R18, shifting the speedometer by -4.25%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-29.0 mm
-4.25%
Speedometer at 100
95.7 km/h
-4.25% error
Ground clearance
-14.5 mm
ride height delta
Sidewall change
-14.5 mm
revs/km: 487.3
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/compare/225-50-r18-vs-245-40-r18Detailed comparison
| Metric | 225/50 R18 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 682.2 mm | 653.2 mm | -29.0 mm (-4.25%) |
| Sidewall height | 112.5 mm | 98.0 mm | -14.5 mm |
| Circumference | 2.143 m | 2.052 m | -91.1 mm |
| Revs / km | 466.6 | 487.3 | +20.7 |
| Ground clearance | reference | -14.5 mm | -14.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.7 km/h | -4.25 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 95.7 km/h after switching to 245/40 R18 — a -4.25% 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 -14.5 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
225/50 R18
Back to
245/40 R18
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