Chris Jeggo wrote:Brucey has mentioned ISO bead seat diameters of 584 and 590 above. These sizes were common in the UK for many years, but under another name. 26" wheels were in the majority, and their overall diameter, including the tyre, was pretty close to that nominal 26". The two common sizes were 26 x 1-3/8" and 26 x 1-1/4", but a tyre so labelled would only fit on a rim identically labelled....
26 x 1-1/4" tyres fit onto 597mm rims.
The reason for 'overcomplicated' answers is because 'simple answers' are usually also wrong answers.
The OP almost got the idea that 28" = 700C = 622mm rims. This is essentially repeated above as if it were true.
It is both wrong, (there are several different -incompatible- 28" sizes in current use) and also fails by omission; you will also find tyres that fit 622mm (BSD Bead Seat Diameter) rims labelled as 29" tyres.
So armed with a 'simple answer' someone could either buy the wong tyre or assume that a given tyre isn't going to fit because it says it is a different size. 'Simple answers' like that are no use to anyone.
The CUK page on tyre sizes is similarly incomplete and needs updating.