Re: Difference? Middleweight/balloon Schwinn
normally, a middleweight has a skinnier fork, fenders, and frame (to go with the skinnier wheels and tires.) a lot of the bikes will take a wider rim, but you'll have to find that out for youself.
also, the rim sizes are usually different. if it's a 1 3/4, it's different from a 1.75, and the tires aren't interchangeable.