I think there are reasons for matching tire size and tube size . I also think you can get away with a narrow tube(700 x 23) in a wider tire 700 x 28 without much problem. In theory , the rubber would not be as thick if inflated beyond its stated application . That said , I really don't worry about the tube being too narrow. I care more about rim tape and tire seating when changing them. My Mondia has 27" x 1 1/4" tires that measure 1.390" when inflated and I am using 700 x 23-28 tubes with many miles and no problems. Joe joesvintageroadbikes.wordpress