What is 315/70R17 in inches?

The width is what this size is bought for

12.40 in. A 35x12.50R17 is 12.50 in. Those two figures are 0.10 in apart, and no other metric light-truck size on a 17-inch wheel comes close to a flotation width. Everything else about 315/70R17 — its popularity, its reputation, the 35-inch label it gets given — follows from that single near-match.

8.68 inches of sidewall, from a 70-series

70% of 315 mm is 220.5 mm. On a 17-inch rim that produces 34.36 in overall, which makes this the tallest metric light-truck size in general circulation on the wheel. Past it there is nothing metric to move to; the catalogue simply hands you over to flotation sizing.

What twelve and a half inches of tire needs from the vehicle

Section width is measured at the widest point of the casing, and on a 315 that point sits well outboard of the tread. The consequences land at the inner edge — steering components, control arms, frame — as often as at the fender, and they scale with steering angle rather than with ride height. This page states the measurement; the clearance is yours to check, at full lock and full compression, on your own vehicle.

The rotation count, and what depends on it

586.9 revolutions per mile. Against a 265/70R17's 638.1 that is a difference of more than fifty turns in every mile, and it is the figure every gearing and speedometer consequence is computed from — not the diameter, which is only the diameter's more legible form.

Beside its immediate neighbour

305/70R17 measures 33.81 in and 12.01 in wide: 0.55 in shorter and 0.39 in narrower. That is the whole choice at the top of the 17-inch metric range, and it is a smaller step than the label difference suggests. Draw the pair, or look at section width against tread width for why 12.40 in of section does not put 12.40 in on the road.