Comparison
235/40 R19 vs 255/45 R18
Minus-sizing from 235/40 R19 to 255/45 R18 pairs a smaller 18-inch wheel with more rubber between the rim and road. This tire combination shifts overall diameter slightly from OEM. The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/45 R18 is 16.1 mm taller than 235/40 R19, shifting the speedometer by +2.40%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+16.1 mm
2.40%
Speedometer at 100
102.4 km/h
+2.40% error
Ground clearance
+8.1 mm
ride height delta
Sidewall change
+20.8 mm
revs/km: 463.5
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/compare/235-40-r19-vs-255-45-r18Detailed comparison
| Metric | 235/40 R19 | 255/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 670.6 mm | 686.7 mm | +16.1 mm (+2.40%) |
| Sidewall height | 94.0 mm | 114.8 mm | +20.8 mm |
| Circumference | 2.107 m | 2.157 m | +50.6 mm |
| Revs / km | 474.7 | 463.5 | -11.1 |
| Ground clearance | reference | +8.1 mm | +8.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.4 km/h | +2.40 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 102.4 km/h after switching to 255/45 R18 — a +2.40% 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 +8.1 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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235/40 R19
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255/45 R18
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