What is 225/45R17 in inches?

The sidewall is the number that matters here

3.99 in. That is 45% of a 225 mm section, converted, and it is what stands between a 17-inch rim and the road surface at each end of the tire. Everything else about this size follows from that figure: the ride, the steering response, the vulnerability of the wheel to a kerb, and the reason a pothole that a truck tire absorbs can bend this one's rim.

Two-thirds wheel, by measurement

17 in of the 24.97 in overall diameter is wheel — 68% of it. What is left is the two sidewalls, 3.99 in at the top and 3.99 in at the bottom. A 195/65R15 stands within a hundredth of the same overall height and gives 4.99 in at each end to the same job.

Wider than it looks, shorter than it sounds

The section is 8.86 in, which is wider than either of the smaller-wheel sizes it commonly replaces, while the overall diameter is essentially the same as theirs. That combination — more width, same height, less sidewall — is the entire content of a plus-size step, and 225/45R17 is one of the most common destinations for one.

One aspect step buys nearly an inch

225/50R17 keeps the section and the rim and raises the aspect ratio by five points, arriving at 25.86 in — 0.89 in taller, and 3.55% on the speedometer. That is a large change for a small edit to the code, and it is the usual route back toward a taller sidewall without giving up the wheel.

What 807.6 revolutions per mile is doing on a page about a car tire

It is the figure that makes this size interchangeable with a 195/65R15 (807.4) without recalibrating anything. Two-tenths of a revolution in eight hundred is not a difference any instrument can express. If you are checking a specific pair rather than these, the comparison runs both sets of numbers side by side, and the aspect ratio reference explains why 45 on a 225 gives less sidewall than 65 on a 195 even though both are percentages of a different base.