I wasn't sure where to put this post so this looks like a good place to start...

My LBS ordered me a pair of Sun CR18 650b rims and after I built them up I went to install the tires and

WTF!!! - Holy cow these tires are almost impossible to get on the rim!

Granted I have the cheap Kenda gumwalls but when they were mounted on the steel Araya rims I had I could dismount them by hand. I could almost swear I must have received the 650A rims by mistake (6mm BCD difference) but I compared them to the old rims and they were the same diameter. By the way my bike is a '91 Schwinn Frontier I converted into a touring/commuter rig with a Sturmey-Archer three-speed rear hub and fenders, Brooks/Carradice etc.

I want to do some long-distance club rides and day tours or maybe some overnight tours but I'm afraid to now since if I get a flat I would be screwed. I never had that hard of a time wrestling tires on rims before like this.

I'm kind of worried now. Should I get new tires? I've rode long distances on the tires I already have and I really like them - low rolling resistance and the bike rides like a Cadillac so I don't want to replace them unless I absolutely have to. Any other 650b owners have any problems with getting tires on/off rims?