26 x 1 3/8 is either a 590 or 597 mm diameter wheel depending on whether it's a Schwinn or not.
The two most common sizes you could switch to is the 26 mtn bike size (559mm) or "700c" (622mm)
650B is a size that has started to regain popularity (584mm) and is the closest to what you've got. But you would have limited rim and tire choices.
What you can fit comes down to clearance on your frame & fork as well as brakes. Remember that these measurements are diameters, so you need to think in terms of radius's to figure out how much room you have to go up or down. Remember too that wider tires are generally taller as well.
My guess would be that you could go down to a 26" mtn rim. But the big worries would be clearance for the tire in the frame/fork and whether your brakes would have enough reach to still hit the rim with the pads.
You are right to worry about tire clearance and making sure that the caliper brake will have long enough reach to get to the rim. I also neglected to mention that if you get pre-built 26" wheels, you'll probably have some issues with the rear axle being too wide for your frame. There's ways to deal with that as well, but it's another thing to deal with...
If you want to put together a beater, winter bike, the cheaper option may actually be just to find a beat up cheaper mtn bike and put some fenders on it. Won't be as fun a project, but depends on your goal
Jan 10, 2013 03:05 PM
Veteran Member San Jose, CA
Joined: Jul 2010
You could replace the fork with one intended for ISO559 rims - I did that on my 310 (the original fork was damaged), but am using a ISO590 rims on the bike front and rear. My 310 originally had ISO630 rims. They did not provide enough clearance for fenders. ISO 622 would not have provided enough extra clearance, so next step with tire choices that suit me is ISO590.
For the back, you can either go long reach brakes, or make an adaptor plate as Sheldon shows.
Linear pull and modern dual pivot side pull brakes are much more effect than earlier brakes - it is amazing the difference.