Comparison
225/40 R19 vs 255/45 R18
Going from 225/40 R19 to 255/45 R18 is a minus-1 setup that adds sidewall on a smaller 18-inch wheel. This alternative fitment 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. More sidewall typically improves comfort and curb protection, especially on city streets. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/45 R18 is 24.1 mm taller than 225/40 R19, shifting the speedometer by +3.64%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+24.1 mm
3.64%
Speedometer at 100
103.6 km/h
+3.64% error
Ground clearance
+12.1 mm
ride height delta
Sidewall change
+24.8 mm
revs/km: 463.5
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/compare/225-40-r19-vs-255-45-r18Detailed comparison
| Metric | 225/40 R19 | 255/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 662.6 mm | 686.7 mm | +24.1 mm (+3.64%) |
| Sidewall height | 90.0 mm | 114.8 mm | +24.8 mm |
| Circumference | 2.082 m | 2.157 m | +75.7 mm |
| Revs / km | 480.4 | 463.5 | -16.9 |
| Ground clearance | reference | +12.1 mm | +12.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 103.6 km/h | +3.64 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 103.6 km/h after switching to 255/45 R18 — a +3.64% 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 +12.1 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.
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225/40 R19
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255/45 R18
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