personal anecdote about rim differences....
several years ago, i picked up a set of deore disc/sun ds-2 rims; not expecting any problem, i started right in putting my 'old' wire-bead tires on them. OH...MY...GAWD!! an HOUR later, i looked at one tire mounted, one finger bleeding (split open from the pressure i was putting on it), and i was telling myself, "no f***ing way".
DS-2's are made specifically for kevlar beads, as, i suspect, most sun rims are; i also have a set of factory specialized rims that are a little tough to mount up even a kevlar bead (although i did do it without a tool).
also had a deore disc/mavic 223 set that mounted up anything you had, no prob. (even a set of -- gasp! -- k-mart specials!)
fwiw, wallyworld now sells kevlar bead tires -- still heavier than elephant sh**, but they mount up well -- have done a couple for customers....