Arthur Peabody

Yesterday my front tube was at 17 psi after a few hours of riding. At home I took it off, couldn't find a leak, pumped it up. It was still 90 psi this morning, but after a couple of hours riding, it was 17 psi. I still can't find a leak - I looked harder this time. I couldn't find anything in the tire, not even with a ball of cotton. The liner and tube protector have nothing in them.

What kind of leak happens only when riding? Stops at 17 psi?

It's a cheap tube, CST, repaired once, last September.

LesterOfPuppets

It's common for a tube to hold air at low pressure. It'll have a small hole that remains closed at low pressure, but opens up as tube is inflated.

Miele Man

I had a tube like that and it had a tiny pin hole in it. It held pressure for awhile but eventually lost it until it reached a certain pressure. What was happening was that after losing a large amount of pressure the tiny hole was so small it was effectively sealed. I finally found that pinhole by taking the tube entirely out of the tire, pumping it up a LOT and then holding small sections of the tube under a large pan of water. I eventually spotted the very small bubbles escaping from the pinhole.

I carry a spare tube to change on the road and I also carry a small bottle of Stan's Tire Sealant to use if I get such a hole again and need that tube.

Cheers

Crankycrank

Pull the tube out inflate and wiggle the stem around and check for tears at the base. I've seen many cracks and tears around the stem that will hold air until it gets ridden and moved around slightly. If you haven't already, submerge the inflated tube in a bucket of water which will release bubbles at the puncture.

texbiker

When I can't find the leak I take the tube, air it up to 80 to 90 psi, and slide the tube through a tub of water slowly and watch for bubbles. This works all the time for me. Regarding the 17 psi, that may be close to the atmospheric pressure where you are and the pressure equalizes with the pressure.

Arthur Peabody

I don't consider a tube inspected for leaks until I have removed it, pumped it up as much as a tube can take (about 2 pounds, according to FBinNY), and putting it in soapy water (soap enhances bubbles.) That I reported that I inspected the inside of the tire, the liner and protector, evidences that I removed the tube.

Sealants have never worked for me. I carry 2 spare tubes, haven't repaired a tube on the road in years.

It looks okay. It's a new tube. Failures around the base of the stem have been obvious to me in the past.

I'm surprised anyone suggests this. It never occurred to me that someone would report a leaky tire before submerging it for a check.

A tube explodes with only a few pounds of pressure. I've done it.

Of course I tried this. I asked here because it didn't work for me this time.


You use a gauge that measures absolute pressure? Does anyone else in the forum? I doubt it. Mine measures relative pressure, the pressure above atmospheric.

tFUnK

Was gonna say check the valve base but you mention it's a new tube.
Is this presta or Schrader? Either way, it could be the valve core. If it's removable presta core you can take it out and inspect/clean the rubber gasket part. It's been a while since I took out a Schrader core but try doing similar. It could just be not screwed in fully. If presta, make sure to close the valve nut tight after inflating.

Arthur Peabody

I replaced the tube with a thorn-resistant (because thick) and, 3 weeks later, the same thing happened: it started leaking only when riding, stopped at 17 psi. I can't find anything wrong. I replaced the tire, though it still has a lot of tread.

shelbyfv

Kind of snippy replies to folks trying to help. I suggest if you are unable to find the leak, replace the tube. Too much drama for a tube.

Juan el Boricua

This. If you come to a forum for the very first time to ask questions because you apparently needed help, people (without knowing your background or yourself) will answer from the very basic "common sense" type to an "almost a thesis dissertation" answer, to help a fellow member. If you wanted a specific answer, maybe ask for comments on your idea?; maybe be open minded; tolerant?
here goes my $0.02: buy a new tube or convert to tubeless and be done with it.
And why would you change a tire when it's the tube failing?

Arthur Peabody

I didn't ask for help. I didn't understand why a tube would act this way. I asked in case someone had a sensible hypothesis.

Because tubes kept failing, and in a way that I couldn't detect despite hundreds of tubes fixed over 50 years of riding.

You impute drama. I intended none.

I did.

I am.

I already had, as someone who read my posts would have known.

shelbyfv

Happy you figured out a solution, with or w/o assistance....

Litespud

I don’t think there’s anywhere on the planet where atmospheric pressure is 17 psi. All pressure gauges measure the pressure wrt ambient (atmospheric). So, a reading of 17 psi simply means that the tire pressure is 17 psi higher than ambient (~14.7 psi). The absolute pressure in the tube would be ~31.7 psi, but that number’s not relevant. Also, if you attempt to inflate a tube to 80-90psi, the pinhole will be the least of your problems

Iride01 

If I leak checked the tube in water and didn't find the leak, I'd put more air in it. If it still didn't show bubbles, I might put more air in it. If I repeat the process too much and the tube blows up. It's only four bucks.

pdlamb

Only $4 for a tube? How long have you had that tube? How many patches does (did?) it have on it?

Iride01 

Well tubes are pretty expendable to me since I do get them so cheap. So typically I don't patch them. I find old tube more useful to cut up into long strips and use them to hold furniture and stuff I build together as the glue dries. For many of those situations, more effective than clamps as odd angles can be handled easier. And many other uses too from simply tying bags shut to using the loop of an entire tube to wrap around something to hang on a hook on the garage wall. So often I'm short of old tubes when I need them since I really don't flat that often.

You can scold me for not using my LBS. But there are plenty of four dollar or less tubes still available online. I got mine from Walmart. Granted they aren't $4.00 anymore and maybe not the last time I bought them either, which was three years ago when I bought a half dozen or so.

https://www.walmart.com/ip/Bell-Stan...5-32c/34038251

https://www.bikeinn.com/bike/contine...mm/137172134/p

https://www.bikeinn.com/bike/bike-pa...1)+asc&start=0

https://www.jensonusa.com/Serfas-Road-Presta-Valve-Tube

robertorolfo

Ah, so asking for hypothesis which could address an issue you are having isn't "asking for help." Got it.

For someone who becomes so irritated by the implication from others that you might lack some knowledge, you seem to have no qualms about doing the same exact thing to other people.

Iride01 

I would think that explaining why a tube acts a certain way is help. Help in understanding. Whether the conversation directly contributed or caused you to have a Eureka moment, it still seems like help.

Miele Man

Not $4.00 a tube where I am. If you're getting tubes for $.00 each then you're very lucky.

I remember the situation I had that was like the O.P.'s. THe tire wiould very slowly lose air, I'd stop and pump it up again and it's very slowly lose air again. Unfortunately on that ridethere was no place where there was water to immerse the tube in to find that pin hole. I now carry two spare tubes and my patch kit. If I get stuck out in really crappy weather, I'll remove the valve core and put in some tire sealant. Those pin holes are precisely what tire sealant excels at filling.

Cheers

WGB 

+1 for a tear at the Presta valve base. I have had at least 3 people ask for help with a flat this year who believed that little nut must be torqued down tight against the rim after inflating.