Comparison
245/40 R19 vs 255/40 R18
Switching from 245/40 R19 to 255/40 R18 steps down to a 18-inch wheel — a familiar move for winter and dedicated all-terrain sets. This swap shifts overall diameter slightly from OEM.
Expect a slight but noticeable shift in indicated speed compared to the original tires. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. Minus-sizing keeps replacement costs down and opens up a wider range of winter and all-terrain tires. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/40 R18 is 17.4 mm shorter than 245/40 R19, shifting the speedometer by -2.56%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-17.4 mm
-2.56%
Speedometer at 100
97.4 km/h
-2.56% error
Ground clearance
-8.7 mm
ride height delta
Sidewall change
+4.0 mm
revs/km: 481.4
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/compare/245-40-r19-vs-255-40-r18Detailed comparison
| Metric | 245/40 R19 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 678.6 mm | 661.2 mm | -17.4 mm (-2.56%) |
| Sidewall height | 98.0 mm | 102.0 mm | +4.0 mm |
| Circumference | 2.132 m | 2.077 m | -54.7 mm |
| Revs / km | 469.1 | 481.4 | +12.3 |
| Ground clearance | reference | -8.7 mm | -8.7 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.4 km/h | -2.56 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 97.4 km/h after switching to 255/40 R18 — a -2.56% 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 -8.7 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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245/40 R19
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255/40 R18
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