It's the 1 3/4 size.Is it bigger than a modern 24in. tire?I dont have a new 24inch to compare. Next to my 26 inch uni wheel the old schwinn wheel is almost as big!
I can't remember if it's bigger or smaller, but one tire definitely will not fit the other. You could probably find this information at Sheldon Brown's site or similar, by searching on "Schwinn S-7 rim" or similar.
-- johnfoss - The wilder Wilder
John Foss, the Uni-Cyclone "jfoss" at "unicycling.com" -- www.unicycling.com