Comparison
225/45 R17 vs 255/40 R18
255/40 R18 is a plus-1 alternative to 225/45 R17 — the bigger wheel shows through a thinner sidewall. This swap 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.
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 26.9 mm taller than 225/45 R17, shifting the speedometer by +4.24%.
Current Tire
New Tire
Ground line · scaled comparison
Slight Difference
Within ±5% — usable, recalibration recommended
Diameter change
+26.9 mm
4.24%
Speedometer at 100
104.2 km/h
+4.24% error
Ground clearance
+13.5 mm
ride height delta
Sidewall change
+0.8 mm
revs/km: 481.4
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/compare/225-45-r17-vs-255-40-r18Detailed comparison
| Metric | 225/45 R17 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 634.3 mm | 661.2 mm | +26.9 mm (+4.24%) |
| Sidewall height | 101.3 mm | 102.0 mm | +0.8 mm |
| Circumference | 1.993 m | 2.077 m | +84.5 mm |
| Revs / km | 501.8 | 481.4 | -20.4 |
| Ground clearance | reference | +13.5 mm | +13.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 104.2 km/h | +4.24 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 104.2 km/h after switching to 255/40 R18 — a +4.24% 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 +13.5 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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225/45 R17
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255/40 R18
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