Tire pressure limited by rim?

[BataviaJim]

1979 Schwinn Traveler III
Last month I bought new tubes and tires -- All Condition Armadillo. (Tires are worth more than the bike but that's all they had in stock and I needed something.)
I took a short test ride, all okay, and hadn't ridden since.
Yesterday they needed inflation. The tires specify 85-95 psi. I inflated to 82 (per gauge on pump, checked with tire gauge). Ten minutes later the tire blew off the rim. Fortunately I wasn't riding.
The bike shop said the problem was the rim couldn't handle more than 70 psi, and they charged me for a new tube because the old one split when it blew.
Can this be possible? I'm skeptical because I inflated the old tires to 80 psi for years. I suspect a defective tube but can't prove it so I paid.

It was a hard blast, deafening (almost literally) in my closed garage. Now I'm hesitant to ride -- I'd have probably been thrown if I was riding when it blew.

Has anyone had this happen, and what makes the most sense?
Thanks.

 

[Cycleops]

What size are the rims and tyres? I can’t open your link. I have Schwann Traveler but much later, about early nineties. I regularly run the tyres at 80+ with Continental TourRides. I suspect as your LBS is right, it’s the rims.

 

[raleighnut]

1979 Schwinn Traveler III
Last month I bought new tubes and tires -- All Condition Armadillo. (Tires are worth more than the bike but that's all they had in stock and I needed something.)
I took a short test ride, all okay, and hadn't ridden since.
Yesterday they needed inflation. The tires specify 85-95 psi. I inflated to 82 (per gauge on pump, checked with tire gauge). Ten minutes later the tire blew off the rim. Fortunately I wasn't riding.
The bike shop said the problem was the rim couldn't handle more than 70 psi, and they charged me for a new tube because the old one split when it blew.
Can this be possible? I'm skeptical because I inflated the old tires to 80 psi for years. I suspect a defective tube but can't prove it so I paid.

It was a hard blast, deafening (almost literally) in my closed garage. Now I'm hesitant to ride -- I'd have probably been thrown if I was riding when it blew.

Has anyone had this happen, and what makes the most sense?
Thanks.

View attachment 602853

If it is a non 'hooked' rim then 65-70 psi is the absolute max

 

[BataviaJim]

The tires are 27 x 1-14. There's no sizing on the rims but they measure 25-1/4 from edge to edge, or maybe an eighth more.

I don't know if the rims are hooked or not. Is there any way to tell with the tires already mounted?

I don't know why there's a permission issue with the pic.
It's just the bike. It should be it inserted here, if it works:

.

 

[BataviaJim]

BTW, when I checked after I got back from the shop yesterday the tires were inflated only to 50 psi. I could see they flattened a little when I rode, and I only weigh 135 lbs. My old tires didn't noticeably flatten. Is it okay that they do now, or should I put more than 50 in? Although as I said I'm leery now and feel safer from a blow-out with lower pressure, but might that pose other problems?

 

[andrew_s]

The pressure the rims can handle is not constant.

As the brake blocks wear the rim away, it gets weaker, and in the end either the rim flange will bend outwards and let go of the tyre, or it will split half way up, spread a bit, and allow the tube to explode through the gap.

 

[DaveReading]

If it is a non 'hooked' rim then 65-70 psi is the absolute max

I learned that lesson the hard way, too.

 

[BataviaJim]

Seems like I can believe the bike shop that the rims were the cause. Although I fault them for not warning me when I bought the tires. They mounted them so they saw the bike and rims. They didn't say a word about inflation, and since 85-95 psi is stamped on the tires, casual riders would inflate to that pressure.

So is it safe to ride if I keep it at 50 psi?

 

[raleighnut]

Seems like I can believe the bike shop that the rims were the cause. Although I fault them for not warning me when I bought the tires. They mounted them so they saw the bike and rims. They didn't say a word about inflation, and since 85-95 psi is stamped on the tires, casual riders would inflate to that pressure.

So is it safe to ride if I keep it at 50 psi?

Yep maybe a bit more, if they are the original 79 rims then they'll almost certainly be straight sided internally. Hooked rims were marked as 'high pressure' rims back then

This is a straight sided rim profile

This is a 'hooked rim profile

this hook grabs onto the tyre bead and prevents 'blow off'

 

[raleighnut]

I learned that lesson the hard way, too.

Yep my old Carlton has 'straight' rims, the 27 x 7/8ths" front tyre is always a compromise between is it hard enough or will it blow off. The rear is a much more sensible 27 x 1 1/8th"

 

[BataviaJim]

Yes, they're the original 1979 rims. And there aren't any markings of any kind on the rims.
It would have been nice if the shop had said something. I don't know how anyone is supposed to know this stuff if you're just a casual rider, especially with the tires marked 85-95 psi.
I'll keep it at 50 psi to be on the safe side.
Thanks for all the advice.

 

[Ming the Merciless]

1 1/4” is 32mm as near as damn it. Unless a heavy rider you wouldn’t go anywhere near 85 psi. I have 32mm on my road bike and rear of recumbent. I have them at 65 psi for rear and 60 psi for front.

 

[BataviaJim]

I'm the opposite of heavy -- I wouldn't crack 140 lbs if I were wearing a parka and snow boots.
And I don't ride hard either -- I'm in my seventies and take it easy.

 

[overmind]

I did not know about hooked rims. Thanks, thats useful to know. I'll check all my rims.

 

[rogerzilla]

The irony is that hookless rims are coming back, facilitated by the current trend for fat 28mm+ tyres on road racing bikes, which can be run at modest pressure.