Had the same idea and checked with Schwalbe. Looks like most sizes in the 650B family will fit. See below:
Bicycle tires designated as 650B have a bead seat of 584 millimeters. They are used on some touring and tandem bicycles as well as Schwinn MTB’s and some rare Raleigh bikes. Schwinn called this size an S-4. Sizes include: 26x1-5/8, 26x1-1/2, 26x1-3/8
Thank you for the tire size guys its a huge help.. The rear had a 26 1 3/8 I believe that looks wrong to me .
I was told a Schwinn 26 1 3/4 would fit but would pop off once inflated over 20 lbs ..
Now to see if i have those tires :roll: ..