How wide is a 265 tire?

The figure is conditional, and the condition is the wheel

265 mm converts to 10.43 in, and that is what a tape measure will read only if the tire is mounted on the rim width the size was specified against. Section width is quoted at a nominal measuring rim, and the casing follows the rim it is fitted to: roughly 0.2 in of section gained per half inch of extra rim width, with a small loss of height at the same time.

The practical consequence is uncomfortable for anyone comparing numbers from two sources. A 265 on a wide wheel can measure across as much as a 275 on a narrow one, and both owners are reporting honestly. The rim width to tire width page sets out the relationship.

What the number pins down, and what it does not

It fixes one dimension of the casing and leaves the rest open. In this catalogue alone, 265 mm appears on sizes ranging from 30.43 in to 32.65 in in overall diameter — 265/50R20 at the short end, 265/75R17 at the tall end, with 265/70R17 at 31.61 in somewhere in the middle. All are 10.43 in wide. Two of them are more than two inches apart in height.

The most common truck width there is

265 is the default across mid-size trucks and full-size SUVs on 16, 17, 18 and 20-inch wheels, which is why the width alone is so often used as shorthand. It is a poor shorthand, precisely because it is so widely used: the same three digits describe a crossover tire and a light-truck tire that share nothing except the distance across their shoulders.

Where the rubber meets the road, which is narrower

Tread width is a separate dimension and always the smaller one — the casing bulges outboard of the contact patch. Compare a 265 against a wider size and the drawing shows section against section, not tread against tread.