Originally Posted by
VegasTriker
It is a good idea to mark the location of the valve on the outside of the tire before you remove the tire after getting a flat. That's so you can exactly line up the the hole in the tube with both the rim and with the inside of the tire casing. This narrows down where you have to look for the cause of the puncture be it on the tire or on the rim. Carefully feel around inside the tire for something protruding through the tire casing. Look at the rim for a burr near where the hole in the tube lines up with its position on the rim. In the worst case you would be far better simply buying a new wheel rather than an entire bike.
I always center the tire label at the valve. No marker needed.
OP, a rim can handle a wide variety of tire widths. Wider rims is the popular tend now but many of us rode wider tires on the older narrow rims years ago without issue. 28s are right in the middle to tire widths and will go on just about anything (assuming the slightly larger tire will fit inside your frame and not run too close to the fork or rear stays or (sometimes) the seat tube.). Pinch flats from not enough pressure or tire size will always show on the rim/underside of the tire, (Look carefully for a second flat about 1 cm to the other side of the tube. That's a pinched tire "snakebite".)
Ben