Comparison
245/45 R17 vs 255/40 R18
Going from 245/45 R17 to 255/40 R18 steps up to a 18-inch rim while trimming sidewall to stay near OEM rolling diameter. This swap lands within OEM rolling-diameter tolerance.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. The larger wheel shows more of the brake hardware and tightens up the wheel-gap look. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick math: 255/40 R18 is 8.9 mm taller than 245/45 R17, shifting the speedometer by +1.36%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+8.9 mm
1.36%
Speedometer at 100
101.4 km/h
+1.36% error
Ground clearance
+4.5 mm
ride height delta
Sidewall change
-8.3 mm
revs/km: 481.4
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/compare/245-45-r17-vs-255-40-r18Detailed comparison
| Metric | 245/45 R17 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 652.3 mm | 661.2 mm | +8.9 mm (+1.36%) |
| Sidewall height | 110.3 mm | 102.0 mm | -8.3 mm |
| Circumference | 2.049 m | 2.077 m | +28.0 mm |
| Revs / km | 488.0 | 481.4 | -6.6 |
| Ground clearance | reference | +4.5 mm | +4.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.4 km/h | +1.36 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 101.4 km/h after switching to 255/40 R18 — a +1.36% 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 +4.5 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
245/45 R17
Back to
255/40 R18
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