Repairing friends 70's Raleigh low end 10 speed. 27x1 1/4" stl rims. Installed Performance
27x 1 1/4" tires. They have blown off the rims at 90 psi twice. I looked inside the rim and
they don't seem to have a hook for the tire bead to seat into. Am I doing something wrong?
Thanks,
Bob H.

You're not doing anything wrong, you're simply trying to run too much presure for an unhooked rim.

Yep. I run #70 max.

Hi Robert, here is a bit of 'tip' after you install the tire inflate to about 50psi. then deflate the tire and go around the tire and be sure you have not 'pinched' the tube under the wire bead. now since you are having trouble with these I would also inflate to about 50 again and roll the wheel across the floor a few times putting some weight on it. then inflate to the recomended sidewall pressure.

don't leave it in the sun either!

Thanks All,
First experience with hookless rims. High limit is now 60 psi

There's absolutely no reason to limit the pressure just because they're straight side rims. The wire bead should hold them on at the tire's full rated pressure. Usually, straight side rims have a shoulder inside and it's critical that the tire is seated evenly on the shoulder all the way around. If any part of the tire is in the center well, that creates slack allowing another part of the tire to lift over the rim.

Since moving one area into the well is how you got the slack to lift the tire over the rim, it's important to reposition and seat the tire properly. Then, inflate to 10-15psi to give it shape & inspect that it's evenly seated all the way around, using the molded markers in the wall as a guide, before inflating to full pressure. Often the tire won't seat properly near the valve, because of the thickness of the tubes reinforced area there, so after mounting, push the valve into the rim taking the tube well into the tire, then pull the valve back down.

+1
The old Schwinn Varsities had tires rated at 75 psi, and we rarely had problems seating tires on their non-hooked steel rims. There were even several lightweight 27 x 1" and 27 x 1 1/8" tires rated at 100 psi that we put on straight-sided aluminum rims without issues.

Robert: if the tires are blowing off, then you need to do as FB or Bianchigrrl suggested. Inflate in increments and double-check that the tire is seated properly before going higher.

My head tells me this is true. Since the bead can't appreciably stretch, then if you have it seated correctly there should be no way the pressure could stretch the bead out enough to pull it above the rim.

However, years of testing this hypothesis have given false results. Some rims and some tires seem to be more prone to this than others, but the raw fact seems to be sometimes unhooked rims will blowout their tires above a certain level of pressure.

jim

These tires go on these rims quite easily with no tools. They were $10 ea on sale, so qc might be a little lax. been running 60 psi in front, no probs.
i put 90 psi in ba ck after 2 hr ride at 80 psi. friend rode the bike home about 2 mi, put in garage for the night. in the morning the tire was off the rim,
and a 1/2" hole in the tube.

I have had bad luck with the Performance Forte 27 inch tires on hookless rims myself.

+1 Bianchigirl's suggestion. Getting the bead seated properly is critical.

I used to commonly run 100psi plus on my old Peugeot with Araya alloy hookless rims.