Comparison
225/55 R17 vs 255/40 R18
Plus-sizing from 225/55 R17 to 255/40 R18 keeps overall diameter close to factory while opening room for a larger 18-inch wheel. This alternative fitment 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. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 255/40 R18 is 18.1 mm shorter than 225/55 R17, shifting the speedometer by -2.66%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-18.1 mm
-2.66%
Speedometer at 100
97.3 km/h
-2.66% error
Ground clearance
-9.0 mm
ride height delta
Sidewall change
-21.8 mm
revs/km: 481.4
Permalink for this comparison:
/compare/225-55-r17-vs-255-40-r18Detailed comparison
| Metric | 225/55 R17 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 679.3 mm | 661.2 mm | -18.1 mm (-2.66%) |
| Sidewall height | 123.8 mm | 102.0 mm | -21.8 mm |
| Circumference | 2.134 m | 2.077 m | -56.9 mm |
| Revs / km | 468.6 | 481.4 | +12.8 |
| Ground clearance | reference | -9.0 mm | -9.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 97.3 km/h | -2.66 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 97.3 km/h after switching to 255/40 R18 — a -2.66% 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 -9.0 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
225/55 R17
Back to
255/40 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 225/55 R17 and 255/40 R18.
225/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.23%
235/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.12%
255/40 R18 vs 265/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.21%
245/40 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.22%
215/60 R17 vs 225/55 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.52%
215/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.61%
225/55 R17 vs 235/55 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.62%
215/55 R17 vs 225/55 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.65%
Related topics