Comparison
215/45 R18 vs 255/40 R17
255/40 R17 drops the rim from 18 to 17 inches versus 215/45 R18, trading wheel size for taller sidewall. This sizing approach trims or stretches rolling diameter by a small margin.
The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. Extra width broadens the footprint for more grip, but check inner liner and strut clearance before fitting. Minus-sizing keeps replacement costs down and opens up a wider range of winter and all-terrain tires. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeTypical choice for a dedicated winter or off-road setup where extra sidewall pays off.
Quick math: 255/40 R17 is 14.9 mm shorter than 215/45 R18, shifting the speedometer by -2.29%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-14.9 mm
-2.29%
Speedometer at 100
97.7 km/h
-2.29% error
Ground clearance
-7.5 mm
ride height delta
Sidewall change
+5.3 mm
revs/km: 500.6
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/compare/215-45-r18-vs-255-40-r17Detailed comparison
| Metric | 215/45 R18 | 255/40 R17 | Difference |
|---|---|---|---|
| Overall diameter | 650.7 mm | 635.8 mm | -14.9 mm (-2.29%) |
| Sidewall height | 96.8 mm | 102.0 mm | +5.3 mm |
| Circumference | 2.044 m | 1.997 m | -46.8 mm |
| Revs / km | 489.2 | 500.6 | +11.5 |
| Ground clearance | reference | -7.5 mm | -7.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.7 km/h | -2.29 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 97.7 km/h after switching to 255/40 R17 — a -2.29% 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 -7.5 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.
Back to
215/45 R18
Back to
255/40 R17
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