Comparison
215/55 R17 vs 255/35 R18
255/35 R18 is a plus-1 alternative to 215/55 R17 — the bigger wheel shows through a thinner sidewall. This wheel and tire pairing swings rolling diameter far enough to feel on the road. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement.
The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 255/35 R18 is 32.6 mm shorter than 215/55 R17, shifting the speedometer by -4.88%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-32.6 mm
-4.88%
Speedometer at 100
95.1 km/h
-4.88% error
Ground clearance
-16.3 mm
ride height delta
Sidewall change
-29.0 mm
revs/km: 500.7
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/compare/215-55-r17-vs-255-35-r18Detailed comparison
| Metric | 215/55 R17 | 255/35 R18 | Difference |
|---|---|---|---|
| Overall diameter | 668.3 mm | 635.7 mm | -32.6 mm (-4.88%) |
| Sidewall height | 118.3 mm | 89.3 mm | -29.0 mm |
| Circumference | 2.100 m | 1.997 m | -102.4 mm |
| Revs / km | 476.3 | 500.7 | +24.4 |
| Ground clearance | reference | -16.3 mm | -16.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.1 km/h | -4.88 km/h |
Verdict: warning
Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.
Speedometer impact
At a true 100 km/h, your dashboard will read 95.1 km/h after switching to 255/35 R18 — a -4.88% 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 -16.3 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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215/55 R17
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255/35 R18
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