Full Answer
Start with the fact that neither of these is the common VB answer. The proven baseline on an 18x9.5 wheel is 255/35R18, and both sizes in this question are deviations from it in different directions.
Run the numbers, because they explain everything.
Factory 245/40R18 has an overall diameter of roughly 25.7 inches.
255/40R18 comes out around 26.0 inches - roughly 1.2 percent taller than stock. You gain 10mm of section width and a noticeably taller sidewall.
265/35R18 comes out around 25.3 inches - roughly 1.6 percent shorter than stock. You gain 20mm of section width and lose sidewall height.
So they are not two points on the same scale. One is taller and modestly wider; the other is shorter and considerably wider.
**255/40** gives you more sidewall, which means more compliance over broken surfaces and more protection for the wheel against potholes. The extra height is also the reason it is the more common source of rubbing complaints on lowered VBs - the taller tire sits closer to the rear flare through the arc. Speedometer will read very slightly slow.
**265/35** gives you the widest contact patch of the three and the sharpest steering response from the shorter sidewall. The tradeoffs are a firmer ride, more vulnerability to pothole damage, more weight, and greater width at the shoulder to clear. Speedometer reads very slightly fast.
Which to choose. If your car is lowered and you have any rubbing concern, 255/35 or 265/35 are safer than 255/40 because both are shorter than stock. If your roads are rough and you value the wheel-protecting sidewall, 255/40 makes sense at stock height. If you autocross or want maximum dry grip and your fitment already clears, 265/35 is the performance answer.
A point worth making: the difference between these in real-world driving is smaller than the difference between a good tire and a mediocre one. Compound and model matter more than 10mm of section width. Choose the tire you want first, then pick whichever of these sizes it comes in that suits your ride height.
And whichever you pick, keep all four matched. On an all-wheel drive car, meaningfully different rolling diameters between axles load the centre differential continuously.
Last updated 8/20/2026