How many revolutions per mile is 285/70R17?

Why a published figure will not match this one exactly

616.6 is a geometric result: the circumference implied by the size code, divided into a mile. A tire manufacturer's catalogue figure for the same size is obtained differently — by rolling a loaded tire and counting — and it typically comes out a few percent higher.

The reason is that a loaded tire is not a circle. The sidewall deflects where the casing meets the road, so the effective radius is smaller than the free radius, so the tire covers slightly less ground per turn and needs slightly more turns to reach a mile. Neither number is wrong. They measure different things, and every figure on this site is the first kind, stated as such.

What the count is actually used for

It is the only tire dimension a vehicle can observe. There is no sensor that measures diameter or section width; there is a sensor that counts wheel rotations, and everything downstream — road speed, distance travelled, the wheel-speed comparisons behind traction and stability control — is derived from that count against a stored constant.

The arithmetic, in one line

A mile is 63,360 in. Divide it by this tire's circumference and 616.6 comes out. Nothing about the wheel diameter, the width or the aspect ratio enters separately; they matter only through the diameter they produce, which is why two tires of very different proportions can share a count exactly.

Comparing it against something else

The whole point of the number is the ratio between two of them. Against a 33x12.50R17 at 611.2 the gap is 5.4 revolutions per mile, or 0.89%; against a 265/70R17 at 638.1 it is 21.5 revolutions, or 3.49%. Those percentages are the speedometer error and the odometer error, unchanged. Set two sizes in the comparison to get the pair worked out, or read revolutions per mile for the full method.