Greetings,
Your tyre should pop on to the rim at a much lower pressure, without a cage I think that 90 psi is dangerous
I would try;
wear safety glasses and keep fingers well away from the wheel rim/tyre rim;
warm the tyre by placing it next to a radiator for a couple of hours;
hold the tyre vertically and try to walk sideways all the way around the inside of the tyre rim;
apply plenty of talcum powder/french chalk inside the tyre and around the tube;
apply fresh tyre soap around the rim and the edges of the bead of the tyre;
place a tourniquet type strap around the circumference of the tyre so as to force the sides outwards whilst preventing the tyre expanding radially;
leave the tyre valve out and as quickly as possible apply air pressure to about 45psi;
if the tyre is still failing to sit properly, try hitting the rim with a plastic/rubber faced mallet and the shock may assist;
the tyre should jump into place after which you can; tighten any rim clamp; release the air pressure; fit the valve core; re-inflate to what ever pressure you use (average is often 15-18psi front and 10-15psi rear depending upon marque and where you intend to ride); fit dust cap; mark alignment of tyre valve to rim position with tippex; leave for a while then retest tyre pressure.
Hope this suggested procedure helps.
TTFN
Hugh.