255/80R17 — an 80-series metric size on a 17-inch wheel

Aspect ratios above 75 have largely disappeared from metric passenger and light-truck sizes. This is one of the survivors. At 80, the sidewall works out at 8.03 in on a 255 mm casing, which is enough to reach 33.06 in of overall diameter on a wheel most tall tires need a much wider casing to clear.

Every catalogued size within an inch of it, on the same wheel

Size	Diameter	Difference	Section width
285/70R17	32.71 in	−0.35 in	11.22 in
33x10.50R17	33.00 in	−0.06 in	10.50 in
33x12.50R17	33.00 in	−0.06 in	12.50 in
255/80R17	33.06 in	—	10.04 in
295/70R17	33.26 in	+0.20 in	11.61 in
305/70R17	33.81 in	+0.75 in	12.01 in
34x10.50R17	34.00 in	+0.94 in	10.50 in

Read the width column and the point of the size becomes clear. Four of the six neighbours are more than an inch wider; the two that are not are both flotation sizes at 10.50 in. Nothing else metric on this wheel gets near 33 in without going past 11 in of section width.

The gap to a flotation 33 is 0.06 in, which is 0.19% — an indicated 70 mph reads 69.9 mph and a hundred indicated miles is 99.8. In height the two are the same tire. In section width they are 2.46 in apart.

No vehicle in this catalogue lists 255/80R17 as either a factory size or a common upgrade, which fits a size whose appeal is narrowness rather than presence.

The nearest thing to it in shape is 33x10.50R17, whose derived aspect ratio is 76 — four points below this one, on a casing half an inch wider. Only 235/85R16 carries a higher aspect ratio anywhere in this catalogue, and that one is on a wheel diameter a generation older.

Circumference is 103.9 in and the geometric revolutions-per-mile figure is 610.0 — noticeably lower than any 17-inch size of comparable width. How the aspect ratio produces those numbers, and why an 80 means something different on a 255 than it would on a 285, is set out in the aspect ratio reference.