245/45R17 — the widest tread on a 17-inch performance wheel

25.68 in overall. 9.65 in of section width. 4.34 in of sidewall. 80.7 in of circumference, 785.3 revolutions per mile.

The size belongs to the last generation of performance cars fitted with 17-inch wheels as their largest option, and it survives as a well-stocked aftermarket size for people who want tread width without going up a wheel.

Widest of the passenger 17s

Size	Section	Sidewall	Diameter
205/50R17	8.07 in	4.04 in	25.07 in
215/50R17	8.46 in	4.23 in	25.46 in
225/50R17	8.86 in	4.43 in	25.86 in
235/45R17	9.25 in	4.16 in	25.33 in
245/45R17	9.65 in	4.34 in	25.68 in

No passenger-class 17-inch size in this catalogue carries more section width than this one, and only 225/50R17 carries more sidewall. It is the widest-and-deepest combination available before the crossover sizes take over the wheel at 245/65R17 and above.

Where the market went instead

The obvious alternatives are all on larger wheels. 245/40R18 measures 25.72 in — 0.14% from this size, same 9.65 in section, 3.86 in of sidewall. 245/35R19 measures 25.75 in with 3.38 in of sidewall. The tread stayed exactly the same width and the casing got thinner three times over.

That is the whole trajectory of the last twenty years of performance fitment, visible in three rows of a table, and this size is the starting point of it.

An unrelated dead heat

205/60R16 measures 25.69 in against this size's 25.68 in — 0.02%. A mid-size saloon's economy fitment and a performance car's widest 17, rolling identically. Their section widths differ by 1.57 in.

Sidewall and rim width

At 4.34 in there is enough casing here to tolerate a spread of rim widths without the stance shifting dramatically, which is one reason the size stayed popular in the aftermarket long after its factory fitments went out of production. How much the width moves per half inch of rim is quantified in the rim width to tire width reference.

The hole above it on this wheel

There is no 245/50R17, no 245/55R17 and no 245/60R17 in this catalogue. The next 245 mm size on a 17-inch wheel is 245/65R17 at 29.54 in, which is 3.86 in taller than this one.

That is a very large gap in a width that is otherwise densely served — 245 mm appears thirteen times here, across five wheel diameters. What it reflects is that a 245 casing was specified for two entirely different jobs on a 17-inch wheel, a performance one at 45-series and a crossover-and-utility one from 65-series upward, and nothing in the middle was ever asked for.

Above 245/65R17 the ladder resumes and behaves normally: 245/70R17 at 30.50 in and 245/75R17 at 31.47 in, in even steps.