Comparison
255/40 R17 vs 275/35 R18
Switching from 255/40 R17 to 275/35 R18 is a plus-1 upgrade that wraps a shorter sidewall around a larger 18-inch wheel. This setup trims or stretches rolling diameter by a small margin. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides.
Expect a slight but noticeable shift in indicated speed compared to the original tires. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 275/35 R18 is 13.9 mm taller than 255/40 R17, shifting the speedometer by +2.19%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+13.9 mm
2.19%
Speedometer at 100
102.2 km/h
+2.19% error
Ground clearance
+7.0 mm
ride height delta
Sidewall change
-5.8 mm
revs/km: 489.9
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/compare/255-40-r17-vs-275-35-r18Detailed comparison
| Metric | 255/40 R17 | 275/35 R18 | Difference |
|---|---|---|---|
| Overall diameter | 635.8 mm | 649.7 mm | +13.9 mm (+2.19%) |
| Sidewall height | 102.0 mm | 96.3 mm | -5.8 mm |
| Circumference | 1.997 m | 2.041 m | +43.7 mm |
| Revs / km | 500.6 | 489.9 | -10.7 |
| Ground clearance | reference | +7.0 mm | +7.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 102.2 km/h | +2.19 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 275/35 R18 — a +2.19% 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 +7.0 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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255/40 R17
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275/35 R18
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