Comparison
225/45 R19 vs 255/40 R18
Switching from 225/45 R19 to 255/40 R18 steps down to a 18-inch wheel — a familiar move for winter and dedicated all-terrain sets. 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. Diameter delta falls in the cautious 3–5% range, where speedometer recalibration and a careful clearance check are worth doing.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 255/40 R18 is 23.9 mm shorter than 225/45 R19, shifting the speedometer by -3.49%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-23.9 mm
-3.49%
Speedometer at 100
96.5 km/h
-3.49% error
Ground clearance
-11.9 mm
ride height delta
Sidewall change
+0.8 mm
revs/km: 481.4
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/compare/225-45-r19-vs-255-40-r18Detailed comparison
| Metric | 225/45 R19 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 685.1 mm | 661.2 mm | -23.9 mm (-3.49%) |
| Sidewall height | 101.3 mm | 102.0 mm | +0.8 mm |
| Circumference | 2.152 m | 2.077 m | -75.1 mm |
| Revs / km | 464.6 | 481.4 | +16.8 |
| Ground clearance | reference | -11.9 mm | -11.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 96.5 km/h | -3.49 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 255/40 R18 — a -3.49% 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 -11.9 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 R19
Back to
255/40 R18
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