I have a restored 1950 Monark Super Deluxe 26" men's bike, that so far I've been unable to ride. My problem is the wheels don't seem to be compatible with any 26 x 2.125 tires. I've tried two sets, the tires are too large in diameter (or the rims are too small) for the tires to be installed correctly. I know I have the original Monark rims, which seem rather flimsy. If I inflate at all the tires are unable to seat and they slip off. Do I need to replace the rims with an aftermarket drop center rim? Any advice would be greatly appreciated. -RJames