In the bicycle world, the tire size in inches is the approximate outer diameter of the tire.

16", 20", 22", 24", 26", 27", 28", 29", etc.

It becomes problematic when there is a choice of widths offered for each tire size. So, to get around the issue, they created numerous rim sizes (and, of course, bicycles and bicycle standards from around the world).

Rim sizes became a little more important when starting to standardize things like "sewup" tires and clincher tires.

The tricky thing is if you choose to mix, say MOPED tires and BICYCLE tires. It can be done in certain situations. I've replaced Schwinn 16x3 bicycle tires with moped tires, and am happy with the result.

For those still riding bikes from the 1950's, it is nice to see that Schwalbe is continuing to support them.

If you really don't want the tires, sell them on Craigslist, E-Bay, or even the bicycle marketplace here.