TLit

The rear wheel has been ok, same brand of tire, Blackburn with gum sidewalls though. I put in 80 psi in that one too, no problems. I'll have to bring it down once I get the bike together again.

davester

Yes, that is correct, at least for most clincher tires. Tubular tires could run higher pressures. I'm not sure when hooked clincher rims first showed up but for my first few bikes in the '60s and early '70s I do remember that 70psi was pushing the envelope and would sometimes result in catastrophic failures.

cudak888 

The OP's bike is a 12-speed Motobecane with what appear to be steel rims. That's neither a big box store bike nor a new bike, it's C&V. I would assume that's why the OP posted here.

Hook beads are also not a "new fad." They've existed for quite a while, to the point that even many cheap 1970's steel rims were hooked bead by virtue of manufacturing convenience. In fact, I've seen more old steel rims that technically have a crude hooked bead than aluminum rims of the same period - where you usually had to get something a bit higher end (Rigida, Super Champion) before you'd get either a bulged or hooked bead.

For the record, while most Wal-Mart level bikes today have flimsy single-wall aluminum rims, they're usually hooked bead. The "behind-the-curve / recent fad" theory doesn't hold up on either count.


That's a straight-sided steel rim with no hook. 70-75 psi maximum.

Also, is that a wire bead (can't be folded) or kevlar bead (can be folded) tire?

Incidentally, the picture is centered on a sliver of old tire stuck to the inner wall of the rim. Advise cleaning it off with a razor blade.

-Kurt

TLit

I put in another innertube courtesy of Walmart and should be ok now. I was overfilling the air down at the local Gulf with what could be an inaccurate gauge. I was putting it at 80 psi but it could have been going a lot higher. I have a basic bicycle pump and a cheapo air gauge that goes up to 50 psi. So as usual penny wise pound foolish.

By the way: Right formula: pressure = force/area so rearranging: force = pressure/area

Trakhak

The check valve in the compressor at a gas station is designed to operate correctly with the high air volume in car tires. Bike tires fill too rapidly and so are prone to blowing off the rim with gas station compressors, especially if the wheels have straight-sided rims.

Most of the people contributing to this thread have learned to rely on their own floor pumps, which inflate tires much more slowly.

smd4

The first piece of advice in any of the bike books from the 70s/80s was, “don’t inflate your tires at the gas station.”

HTupolev

This isn't a Walmart bike, and hookless was the clincher norm for a very long time until hooks started to take over during the 1970s.

dddd

Rearranging further, force actually equals pressure X area.

I routinely inflated my various 27x1-1/4" wire-bead tires to 90psi on hookless steel and alloy rims (Araya, Sturmey, Ukai, Rigida, etc.) back in the 70's with no blow-offs.
I believe that my Medai/MDI floor pump was accurate, at least it agreed with my other gauges. Tires were IRC and other common gumwalls, though Michelins were fatter so had a lower pressure rating.

Some of the nicer 27x1-1/8" tires that came on sport-touring bikes with straight-sided rims in the late 1970's were rated at 100psi or even 105psi, and we had no problems with them at the Fuji dealer where I worked. Everybody inflated tires to the number on the sidewall back then.

It was only in the 2000's that I bought a 1971 Schwinn Supersport which had hookless alloy Weinmann rims, which would allow the tire to blow off at pressures above 80psi but on the rear wheel only. That was a quality-control issue, and I had to line the irregularly-shaped inside of the rear rim from wall-to-wall with thick, wide cloth tape (easier said than done) in order to run 80psi reliably.

repechage

more info, more questions.
"blew" off the rim... tube should have a long rupture.
brand of tire and rim even way back could be an issue.
steel or aluminum rim?
the notation of $35 for a wheel truing...to me that means time - time to check the spokes and see if any extend beyond the nipple- if so, need to be ground off.
then rim tape.

a dented rim of the mid 70's can spread a bit in a short span- a possible location of a tire popping off.

cudak888 

The OP's pictures tell all, folks. You're all dissing in the wind if you haven't taken a second to study them.

-Kurt

Trueblood

Ha, just happened to me over the weekend, was running at 70psi, nothing wrong with spokes or the rim. Damaged the sidewall - separated it from the wire bead a little - Schwalbe HS159. I could still ride with it after changing the tube, but there was a small bulge in the sidewall. Replaced the tire, now leaving it at 60psi. It was the front wheel. Here's a hint, if you hear a thump thump thump as you ride and you look down and the wheels appear true and the tires are not flat (yet), stop and let a little air out.