what the sidewall marking is made of and what it works out to
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
All figures are ISO 4000-1:2021. The five sections are drawn at one scale; diameters and rims are calculated from the marking, not measured.
In the marking 205/55 R16 the first number is millimetres, the second is not a length at all but a per cent of the first, and the third is a rim code taken from inches. The first two describe the tyre, the third describes the wheel it is fitted to.
This is why the middle number cannot be compared across sizes. The same 55 gives a sidewall of 112.8 mm on a 205 tyre and of 140.3 mm on a 255 one, a difference of nearly three centimetres under an identical figure.
And it is why five markings with no number in common come out as the same wheel. 195/65 R15, 205/55 R16, 225/45 R17, 245/35 R18 and 255/30 R19 work out to between 629 and 636 mm, a spread of 1.1 per cent. The rim gains an inch and the sidewall gives exactly that inch back.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 9 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
frame, wheel by ISO 5775 and handlebar — three signs of a class, and what the frame is rated for
segments A to F by length and bodies by box count — how to name any car you see
rake, trail, wheelbase and seat height — six classes drawn at one scale
nine lines of comparison, and in three of them the requirement is the same for both