Schwinn used some odd tire sizes. The most common we see are the 26 x 1 3/8" and 26 x 1 3/4".
Fitting a tire to a rim is all about "bead diameter" which is printed on most tires.
Below are links explaining it:
http://www.sheldonbrown.com/tire-sizing.html
https://www.sheldonbrown.com/rim-sizing.html
From http://www.sheldonbrown.com/chicago-schwinns.html
"In general, U. S.-made Schwinns take oddball Schwinn size tires, with the exception of 630 mm/27 inch, which is standard.
Good mathematics doesn't always help you when it comes to bicycle tires. For example, most "middleweight" Schwinns take 26 x 1 3/4 tires, which are hard to find, not 26 x 1.75 as used on other brands. You might think that these are the same, but they are not.
The 26 x 1.75 size is the normal I.S.O. 559 mm size used on most mountain bikes; the 26 x 1 3/4 (I.S.O. 571 mm) is not interchangeable with any normal tire of similar width, although its bead circumference is the same as the "650C" size used on some high performance 26" wheel bicycles.
Designating the width with a fraction instead of a decimal usually signifies a straight-sided rim, not a hook-edge rim. The rim/tire diameter is also slightly different. Let the tire buyer beware! There are similar problems with other Schwinn tire sizes. The most common difficulty is that the Schwinn 26 x 1 3/8 (I. S.O. 597 mm) interchanges with the British 26 x 1 1/4, not the British 26 x 1 3/8 (I. S.O. 590 mm)."
Fitting a tire to a rim is all about "bead diameter" which is printed on most tires.
Below are links explaining it:
http://www.sheldonbrown.com/tire-sizing.html
https://www.sheldonbrown.com/rim-sizing.html
From http://www.sheldonbrown.com/chicago-schwinns.html
"In general, U. S.-made Schwinns take oddball Schwinn size tires, with the exception of 630 mm/27 inch, which is standard.
Good mathematics doesn't always help you when it comes to bicycle tires. For example, most "middleweight" Schwinns take 26 x 1 3/4 tires, which are hard to find, not 26 x 1.75 as used on other brands. You might think that these are the same, but they are not.
The 26 x 1.75 size is the normal I.S.O. 559 mm size used on most mountain bikes; the 26 x 1 3/4 (I.S.O. 571 mm) is not interchangeable with any normal tire of similar width, although its bead circumference is the same as the "650C" size used on some high performance 26" wheel bicycles.
Designating the width with a fraction instead of a decimal usually signifies a straight-sided rim, not a hook-edge rim. The rim/tire diameter is also slightly different. Let the tire buyer beware! There are similar problems with other Schwinn tire sizes. The most common difficulty is that the Schwinn 26 x 1 3/8 (I. S.O. 597 mm) interchanges with the British 26 x 1 1/4, not the British 26 x 1 3/8 (I. S.O. 590 mm)."
