Originally Posted by
fietsbob
RIM? you need a Hook bead, straight sided ones wont hold the tire on at more than a modest PSI.
Not true!
IRC was making 27x1-1/4" HP 90psi tires long before hook edge rims came to market. They worked flawlessly on straight side steel and aluminum rims of the era. As of 3 years ago they were still in production and available for sale in the USA at very low prices, and still working fine on straight side rims.
These were not the only HP 27" tires that worked on straight side rims.
However it is true that tires designed around hook edge rims, may not hold their full rated pressure with straight rims. The hook design provides a mechanical interlock allowing the tire maker to use a lighter (stretchier) bead wire.
Sine tires have a large reserve for over inflation, most cases of blowoff are not because of a misfit on the rims, but because of user error in the form of poor seating when mounted.