Comparison
225/45 R18 vs 255/40 R17
Minus-sizing from 225/45 R18 to 255/40 R17 pairs a smaller 17-inch wheel with more rubber between the rim and road. This swap noticeably changes overall diameter compared to OEM. Indicated speed will drift far enough that recalibration is worth considering. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 255/40 R17 is 23.9 mm shorter than 225/45 R18, shifting the speedometer by -3.62%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-23.9 mm
-3.62%
Speedometer at 100
96.4 km/h
-3.62% error
Ground clearance
-12.0 mm
ride height delta
Sidewall change
+0.8 mm
revs/km: 500.6
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/compare/225-45-r18-vs-255-40-r17Detailed comparison
| Metric | 225/45 R18 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 659.7 mm | 635.8 mm | -23.9 mm (-3.62%) |
| Sidewall height | 101.3 mm | 102.0 mm | +0.8 mm |
| Circumference | 2.073 m | 1.997 m | -75.1 mm |
| Revs / km | 482.5 | 500.6 | +18.1 |
| Ground clearance | reference | -12.0 mm | -12.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.4 km/h | -3.62 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 96.4 km/h after switching to 255/40 R17 — a -3.62% 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 -12.0 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
225/45 R18
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255/40 R17
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