There was a reason Schwinn made the S-7 a different diameter. The middleweight tires were not only narrower, the profile of the tire was smaller. So to counter that trying to keep the overall circumference the same as a 2.125 tire and at 26 inches, they made the rim larger keeping the overall circumference the same. For the car tire a 70 series tire fits the same size rim as a 40 series tire but the overall diameter is smaller. All the other bike brands had 25.5 tires, not 26” tires. I’ve heard that an S7 rim and Schwinn tire marked 26 x 2 x 1 3/4 is too big to fit some middleweight Murray’s or huffys.