You should have no problem getting a 26X3.0 on a stock 1.75 rim. I have 3.0 tires on stock width 20 and 24" wheels. The problem you are going to run into is drive chain clearance. Caliper brakes may cause another problem. I have had that problem with 2.125 cruiser tires(chain rub). One cure, drive sprocket placement and motor offset from center. My cure was jackshaft and gears, disc brakes. Cycles U.S. has the 3.0 tires. I am sure many other places do too. Also, the adaptor kits to use a three piece crank have worked good for me. Then you can use a sealed cartridge crank bearings. They come stock, wide one side or both.