Comparison
235/45 R18 vs 255/45 R18
Stepping from 235/45 R18 to 255/45 R18 keeps the 18-inch wheel but widens the section by 20 mm. This sizing approach moves rolling diameter a touch off the original spec. 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. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 255/45 R18 is 18.0 mm taller than 235/45 R18, shifting the speedometer by +2.69%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+18.0 mm
2.69%
Speedometer at 100
102.7 km/h
+2.69% error
Ground clearance
+9.0 mm
ride height delta
Sidewall change
+9.0 mm
revs/km: 463.5
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/compare/235-45-r18-vs-255-45-r18Detailed comparison
| Metric | 235/45 R18 | 255/45 R18 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 686.7 mm | +18.0 mm (+2.69%) |
| Sidewall height | 105.8 mm | 114.8 mm | +9.0 mm |
| Circumference | 2.101 m | 2.157 m | +56.5 mm |
| Revs / km | 476.0 | 463.5 | -12.5 |
| Ground clearance | reference | +9.0 mm | +9.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.7 km/h | +2.69 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 102.7 km/h after switching to 255/45 R18 — a +2.69% 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 +9.0 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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235/45 R18
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255/45 R18
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