You have but one size to choose- 26x1 3/4. With a bit of hunting around you can find a couple different tread styles and black or white wall options. I personally hate s-7 wheels.
My 2 speed is on a S7 wheel, but it's straight so I haven't relaced it into a standard wheel. So it has a 26 x 2 x 1/3/4 tire, the widest but still too skinny for my balloon tire Schwinn.