Comparison
215/60 R17 vs 255/40 R18
255/40 R18 is a plus-1 alternative to 215/60 R17 — the bigger wheel shows through a thinner sidewall. This setup swings rolling diameter far enough to feel on the road. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides.
Indicated speed will drift far enough that recalibration is worth considering. 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: 255/40 R18 is 28.6 mm shorter than 215/60 R17, shifting the speedometer by -4.15%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
-28.6 mm
-4.15%
Speedometer at 100
95.9 km/h
-4.15% error
Ground clearance
-14.3 mm
ride height delta
Sidewall change
-27.0 mm
revs/km: 481.4
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/compare/215-60-r17-vs-255-40-r18Detailed comparison
| Metric | 215/60 R17 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 689.8 mm | 661.2 mm | -28.6 mm (-4.15%) |
| Sidewall height | 129.0 mm | 102.0 mm | -27.0 mm |
| Circumference | 2.167 m | 2.077 m | -89.8 mm |
| Revs / km | 461.5 | 481.4 | +20.0 |
| Ground clearance | reference | -14.3 mm | -14.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 95.9 km/h | -4.15 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 95.9 km/h after switching to 255/40 R18 — a -4.15% 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 -14.3 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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215/60 R17
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255/40 R18
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