Tire pressure limited by rim?

[Arrowfoot]

I agree that the shop didn't need to tell me, but it was the decent thing to do. Of course they got another $20 from me for a new tube after the blow-out, but they also reaped some ill will. Next time I'll go to a different shop.

It seems like most people here are aware of the pressure issue but I don't know how non-experts are supposed to know, especially when there's so much misinformation from apparently expert sources. For example, these websites:
www.sixthreezero.com:

How Much Air Should Be in My Bike Tires?​

The recommended air pressure is written on the side of your tires in embossed lettering. Simply fill your tires with a pump and check with a gauge that the pressure matches the recommended range.​

www.theproscloset.com

Conveniently, every bike tire has recommended PSI stamped into the rubber on the sidewall.​

Here are some more specific recommended starting points for your tires:​

Mountain bike tires: 25 PSI​

Gravel bike tires: 40 PSI​

Road bike tires: 90 PSI​

​

https://communitycyclingcenter.org

Decoding all those numbers: If you look closely at the side wall of the tire you’re likely to find a few sets of numbers embossed in the rubber, but what do they mean?​

Recommended minimum and maximum tire pressure: Skinny, road racing tires might range from 90-130psi.​

​

Note that they all say that the psi stamped on the tire is the recommended pressure, NOT the maximum pressure. My recent blow-out proved to me that's incorrect, but how was supposed to know that unless the shop had told me?


Thanks, that's what I'll do.

Actually you are in the majority and in the main stream. Thats an old rim and tyre manufacturers specification on the tyre wall are for contemporary rims.

With the recent advent of wider tyres and tubeless, people are mixing up old and new technology narratives. I do agree that the LBS should have explained why the tyre blew by looking at the rim. Tyres don't just blow.

Even today if you are on clinchers and on 25/ 28, the expectation is between 90 and 110 psi. No change here despite all irrelevant recent narratives to drop the psi. The only thing it does is a more comfortable ride for a beginner who has yet to be saddle broke. For the seasoned cyclist they would operate in the 90 and above range. Again with clinchers and 25/ 28. A seasoned cyclist will know exactly why they need to operate at that psi range and why tyre manufacturers put that specs.

So the only single issue that is relevant is that it is an old rim.

Btw the way, the hooked design is brilliant. The move to head towards hookless for tubeless is out of necessity and compromise not an innovation. Tubeless beads are stronger to keep the seal but tougher to mount and remove on a hooked rim. The universal standards for tubeless is still not in place.

 

[Ajax Bay]

OP still doesn't know whether their rim is hooked or not, because they aren't prepared to even replace a tube. I assume they have a recovery plan when they get a puncture. The hookless thing is a complete red herring - or at least one that could easily be resolved.
$15 for replacing a tube is well above my hourly rate, btw.

 

[BataviaJim]

OP still doesn't know whether their rim is hooked or not, because they aren't prepared to even replace a tube. I assume they have a recovery plan when they get a puncture. The hookless thing is a complete red herring - or at least one that could easily be resolved.
$15 for replacing a tube is well above my hourly rate, btw.

My recovery plan for a puncture is to walk the bike back home. As I said, I'm nearly 74 years old and the farthest away I ride is 5 miles.

As far as whether the rim is hooked or not, it's almost certain they aren't. Hooked rims were uncommon in the 1970s. I found the Schwinn catalog for my bike and it's not in the extensive description. Also I already know that the upper limit is less than 80psi because that's when it blew, and a hooked rim should have been able to handle that. Since, at 135 lbs, I can ride with the tires at 50 - 55 psi, I don't really see the need to explore this in depth.

BTW, when I was young I used to repair punctures myself, as well as a lot of other stuff I don't do anymore. Surprisingly, things change between the ages of 14 and 74.

 

[Ajax Bay]

if they are the original 79 rims then they'll almost certainly be straight sided internally.

Are you saying that most rims made in 1979 were hookless?

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.

If you mean that hookless rims are appearing as a niche in the market: agreed. Otherwise (adopt pantomime voice) "Oh no they're not!" As you imply below: marketing BS.

https://www.cyclingweekly.com/news/product-news/what-are-hookless-rims-and-do-you-need-them-468466
In bikes, what goes around comes around, and lessons are rarely learnt! The industry attracts marketeers more than engineers.

Btw the way, the hooked design is brilliant. The move to head towards hookless for tubeless is out of necessity and compromise not an innovation. Tubeless beads are stronger to keep the seal but tougher to mount and remove on a hooked rim. The universal standards for tubeless is still not in place.

Necessity? Compromise? Please elaborate. The universal standards you mention isn't in place is for hookless rim/tubeless tyre compatibility, not tubelss tyres per se.

DT Swiss line on rim design and the merits of it being hooked (my daughter has one of these ARC Disc 1100s for competition):
"In terms of safety for bikes that require a relatively high pressure in combination with relatively wide tires, we are convinced that hooked rims are technically the optimal rim construction.
"The ARC 1100 DICUT DISC wheel optimized for 28 mm tires possesses a hooked rim design that holds the tire beads safely in place and lowers the risk of a tire blow-off due to inappropriate tire pressures. With the possibility of riding tubeless as well as tube type systems, the ARC 1100 DICUT DISC offers the rider the possibility to choose from a wide range of tires."

 

[raleighnut]

Are you saying that most rims made in 1979 were hookless?

no i'm saying there were a lot about back then, even into the 80s, I had some wheels made when I rebuilt my Carlton after a lorry ran it over a bit in 85 and they're 27" single wall eyeleted straight sided (ie 'hookless') still going strong Admittedly I don't ride that bike much these days but that's mainly down to the gearing

I ued to be able to get up hills on this

 

[Arrowfoot]

Necessity? Compromise? Please elaborate. The universal standards you mention isn't in place is for hookless rim/tubeless tyre compatibility, not tubelss tyres per se.

DT Swiss line on rim design and the merits of it being hooked (my daughter has one of these ARC Disc 1100s for competition):
"In terms of safety for bikes that require a relatively high pressure in combination with relatively wide tires, we are convinced that hooked rims are technically the optimal rim construction.
"The ARC 1100 DICUT DISC wheel optimized for 28 mm tires possesses a hooked rim design that holds the tire beads safely in place and lowers the risk of a tire blow-off due to inappropriate tire pressures. With the possibility of riding tubeless as well as tube type systems, the ARC 1100 DICUT DISC offers the rider the possibility to choose from a wide range of tires."
View attachment 603937

Yes, meant on rims / tubeless compatibility. My mistake. Note Mavic attempt, now the battle with Giant etc to do some standards. Personally I am for hooked as mentioned in my post. The challenge is mounting tubeless which is becoming harder as the beads are stronger to keep the seal. Hence the mention of compromises by manufacturers, going towards lower psi to hold the seal for less than wide tyres.

I will look into the DT Swiss line, looks good.