Comparison
215/45 R18 vs 255/40 R18
Stepping from 215/45 R18 to 255/40 R18 keeps the 18-inch wheel but widens the section by 40 mm. This swap shifts overall diameter slightly from OEM. Expect a slight but noticeable shift in indicated speed compared to the original tires. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeReasonable performance-leaning swap as long as fender and suspension clearance check out.
Quick math: 255/40 R18 is 10.5 mm taller than 215/45 R18, shifting the speedometer by +1.61%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+10.5 mm
1.61%
Speedometer at 100
101.6 km/h
+1.61% error
Ground clearance
+5.3 mm
ride height delta
Sidewall change
+5.3 mm
revs/km: 481.4
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/compare/215-45-r18-vs-255-40-r18Detailed comparison
| Metric | 215/45 R18 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 650.7 mm | 661.2 mm | +10.5 mm (+1.61%) |
| Sidewall height | 96.8 mm | 102.0 mm | +5.3 mm |
| Circumference | 2.044 m | 2.077 m | +33.0 mm |
| Revs / km | 489.2 | 481.4 | -7.8 |
| Ground clearance | reference | +5.3 mm | +5.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.6 km/h | +1.61 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 101.6 km/h after switching to 255/40 R18 — a +1.61% 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 +5.3 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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215/45 R18
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255/40 R18
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