Comparison
235/55 R17 vs 275/40 R18
Switching from 235/55 R17 to 275/40 R18 is a plus-1 upgrade that wraps a shorter sidewall around a larger 18-inch wheel. This alternative fitment moves rolling diameter a touch off the original spec. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input.
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.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 275/40 R18 is 13.1 mm shorter than 235/55 R17, shifting the speedometer by -1.90%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-13.1 mm
-1.90%
Speedometer at 100
98.1 km/h
-1.90% error
Ground clearance
-6.5 mm
ride height delta
Sidewall change
-19.3 mm
revs/km: 470.0
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/compare/235-55-r17-vs-275-40-r18Detailed comparison
| Metric | 235/55 R17 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 690.3 mm | 677.2 mm | -13.1 mm (-1.90%) |
| Sidewall height | 129.3 mm | 110.0 mm | -19.3 mm |
| Circumference | 2.169 m | 2.127 m | -41.2 mm |
| Revs / km | 461.1 | 470.0 | +8.9 |
| Ground clearance | reference | -6.5 mm | -6.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.1 km/h | -1.90 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 98.1 km/h after switching to 275/40 R18 — a -1.90% 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 -6.5 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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235/55 R17
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275/40 R18
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