Comparison
235/35 R19 vs 255/40 R18
Minus-sizing from 235/35 R19 to 255/40 R18 pairs a smaller 18-inch wheel with more rubber between the rim and road. This tire combination moves rolling diameter a touch off the original spec. 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. 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: 255/40 R18 is 14.1 mm taller than 235/35 R19, shifting the speedometer by +2.18%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+14.1 mm
2.18%
Speedometer at 100
102.2 km/h
+2.18% error
Ground clearance
+7.1 mm
ride height delta
Sidewall change
+19.8 mm
revs/km: 481.4
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/compare/235-35-r19-vs-255-40-r18Detailed comparison
| Metric | 235/35 R19 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 647.1 mm | 661.2 mm | +14.1 mm (+2.18%) |
| Sidewall height | 82.3 mm | 102.0 mm | +19.8 mm |
| Circumference | 2.033 m | 2.077 m | +44.3 mm |
| Revs / km | 491.9 | 481.4 | -10.5 |
| Ground clearance | reference | +7.1 mm | +7.1 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.2 km/h | +2.18 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 102.2 km/h after switching to 255/40 R18 — a +2.18% 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 +7.1 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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235/35 R19
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255/40 R18
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