Comparison
245/45 R18 vs 265/40 R18
Stepping from 245/45 R18 to 265/40 R18 keeps the 18-inch wheel but widens the section by 20 mm. This swap lands within OEM rolling-diameter tolerance.
Dashboard speed shifts only marginally — within the noise of normal OEM tolerance. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Overall the swap sits inside the safe ±3% diameter window, so ABS, traction control and gearing behave normally.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick math: 265/40 R18 is 8.5 mm shorter than 245/45 R18, shifting the speedometer by -1.25%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-8.5 mm
-1.25%
Speedometer at 100
98.7 km/h
-1.25% error
Ground clearance
-4.3 mm
ride height delta
Sidewall change
-4.3 mm
revs/km: 475.7
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/compare/245-45-r18-vs-265-40-r18Detailed comparison
| Metric | 245/45 R18 | 265/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 677.7 mm | 669.2 mm | -8.5 mm (-1.25%) |
| Sidewall height | 110.3 mm | 106.0 mm | -4.3 mm |
| Circumference | 2.129 m | 2.102 m | -26.7 mm |
| Revs / km | 469.7 | 475.7 | +6.0 |
| Ground clearance | reference | -4.3 mm | -4.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.7 km/h | -1.25 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 98.7 km/h after switching to 265/40 R18 — a -1.25% 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 -4.3 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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245/45 R18
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265/40 R18
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