Comparison
225/45 R19 vs 245/40 R18
Going from 225/45 R19 to 245/40 R18 is a minus-1 setup that adds sidewall on a smaller 18-inch wheel. This swap swings rolling diameter far enough to feel on the road. 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: 245/40 R18 is 31.9 mm shorter than 225/45 R19, shifting the speedometer by -4.66%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-31.9 mm
-4.66%
Speedometer at 100
95.3 km/h
-4.66% error
Ground clearance
-15.9 mm
ride height delta
Sidewall change
-3.3 mm
revs/km: 487.3
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/compare/225-45-r19-vs-245-40-r18Detailed comparison
| Metric | 225/45 R19 | 245/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 685.1 mm | 653.2 mm | -31.9 mm (-4.66%) |
| Sidewall height | 101.3 mm | 98.0 mm | -3.3 mm |
| Circumference | 2.152 m | 2.052 m | -100.2 mm |
| Revs / km | 464.6 | 487.3 | +22.7 |
| Ground clearance | reference | -15.9 mm | -15.9 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.3 km/h | -4.66 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 95.3 km/h after switching to 245/40 R18 — a -4.66% 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 -15.9 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.
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225/45 R19
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245/40 R18
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