Blame it somewhat on the mfrs. trying to wow buyers with "new and better" sized tires and old standards. There is the ISO (International Standards Org) which is the most rational and accurate measuring system and printed on almost all current tire sidewalls along with the non-sensical sizes we're most used to. 700c/28"/29" all have a BSD (Bead Seat Diameter) of 622mm which is what you should see on your 28" marked on the tire. ISO widths will also be marked in mm so should read "45-622", easy. As mentioned, post #1 gives a link to the Sheldon Brown article that explains it all when you want to know sizes for other tires and eye opening when buying 26" tires. Hopefully this answers the questions, and this thread can rest in peace.