Comparison
235/45 R18 vs 255/40 R18
Stepping from 235/45 R18 to 255/40 R18 keeps the 18-inch wheel but widens the section by 20 mm. This sizing approach lands within OEM rolling-diameter tolerance. Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Expect a more planted steering feel, at the cost of some of the cushioning a taller sidewall provides. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 255/40 R18 is 7.5 mm shorter than 235/45 R18, shifting the speedometer by -1.12%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-7.5 mm
-1.12%
Speedometer at 100
98.9 km/h
-1.12% error
Ground clearance
-3.8 mm
ride height delta
Sidewall change
-3.8 mm
revs/km: 481.4
Permalink for this comparison:
/compare/235-45-r18-vs-255-40-r18Detailed comparison
| Metric | 235/45 R18 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 668.7 mm | 661.2 mm | -7.5 mm (-1.12%) |
| Sidewall height | 105.8 mm | 102.0 mm | -3.8 mm |
| Circumference | 2.101 m | 2.077 m | -23.6 mm |
| Revs / km | 476.0 | 481.4 | +5.4 |
| Ground clearance | reference | -3.8 mm | -3.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.9 km/h | -1.12 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 98.9 km/h after switching to 255/40 R18 — a -1.12% 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 -3.8 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
235/45 R18
Back to
255/40 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 235/45 R18 and 255/40 R18.
235/45 R18 vs 265/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
225/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.23%
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%
235/45 R18 vs 275/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
235/45 R18 vs 245/45 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.35%
225/45 R18 vs 235/45 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.36%
215/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.61%
Related topics