Comparison
235/40 R19 vs 245/45 R18
Minus-sizing from 235/40 R19 to 245/45 R18 pairs a smaller 18-inch wheel with more rubber between the rim and road. This setup lands within OEM rolling-diameter tolerance.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. The taller sidewall adds cushioning over potholes and rougher roads, with a softer overall ride. 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 change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakePractical direction for winter wheels, chains, or rougher pavement where cushioning matters.
Quick math: 245/45 R18 is 7.1 mm taller than 235/40 R19, shifting the speedometer by +1.06%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+7.1 mm
1.06%
Speedometer at 100
101.1 km/h
+1.06% error
Ground clearance
+3.6 mm
ride height delta
Sidewall change
+16.3 mm
revs/km: 469.7
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/compare/235-40-r19-vs-245-45-r18Detailed comparison
| Metric | 235/40 R19 | 245/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 670.6 mm | 677.7 mm | +7.1 mm (+1.06%) |
| Sidewall height | 94.0 mm | 110.3 mm | +16.3 mm |
| Circumference | 2.107 m | 2.129 m | +22.3 mm |
| Revs / km | 474.7 | 469.7 | -5.0 |
| Ground clearance | reference | +3.6 mm | +3.6 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.1 km/h | +1.06 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 101.1 km/h after switching to 245/45 R18 — a +1.06% 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 +3.6 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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245/45 R18
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