Comparison
255/45 R19 vs 275/40 R18
275/40 R18 drops the rim from 19 to 18 inches versus 255/45 R19, trading wheel size for taller sidewall. This setup noticeably changes overall diameter compared to OEM.
Indicated speed will drift far enough that recalibration is worth considering. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. The smaller wheel is also lighter and easier to find affordable winter rubber for. 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: 275/40 R18 is 34.9 mm shorter than 255/45 R19, shifting the speedometer by -4.90%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-34.9 mm
-4.90%
Speedometer at 100
95.1 km/h
-4.90% error
Ground clearance
-17.4 mm
ride height delta
Sidewall change
-4.8 mm
revs/km: 470.0
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/compare/255-45-r19-vs-275-40-r18Detailed comparison
| Metric | 255/45 R19 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 712.1 mm | 677.2 mm | -34.9 mm (-4.90%) |
| Sidewall height | 114.8 mm | 110.0 mm | -4.8 mm |
| Circumference | 2.237 m | 2.127 m | -109.6 mm |
| Revs / km | 447.0 | 470.0 | +23.0 |
| Ground clearance | reference | -17.4 mm | -17.4 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.1 km/h | -4.90 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 95.1 km/h after switching to 275/40 R18 — a -4.90% 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 -17.4 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
255/45 R19
Back to
275/40 R18
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