Slow leak tires but no tube bubbles in water
 

Have 2 POS bikes taken from someone's garbage trying to fix up. Both have slow leaks in I think all 4 tires. I fill with air and a few months/weeks later they're dead flat. So I went to patch them today after I received my vulcanizing patch glue (thanks forum for the recommendation!). I inflated them totally and put in a bucket of water and slowly fed the tubes through the still water and didn't see a single bubble.
Maybe once the valve caps are screwed on they're causing slow leaks?
fed up with tubes and tire repair, hopefully my good bike I get they make flat-free that is as good as it sounds.
Thanks

Rubber is not completely impervious to the passage of air, especially if the rubber is quite thin as is the case for most bike tubes. So it's not unusual for the air to leak out over a period of months. There are heavier bike tubes that are thicker (marketed as 'thorn-resistant') which would lose pressure more slowly. But these have other disadvantages: greater weight, greater rolling resistance, slightly less comfort on bumpy surfaces.

Did you check the valve cores?

@bikebike3 You are most likely testing for bubbles with minimal air pressure in the tube and unmounted, try taking it up a notch, overinflating the tubes per say, and see if your bubbles appear.

Your profile does not say where you are located but here in Florida it is known that you have to check your air (both cars and bikes) more frequently due to the hot weather.

Your leaving them for weeks, and surprised that they have lost pressure!

I agree with Joe. Small inner tube holes may not be apparent at very low air pressures.

the time expectation and the stated

I suggest buying new heavy duty - thorn resistant tubes .. they're thick so retains air longer,
given coming back weeks later and having not lost much air is important to you..

they're heavy , but on a BSO that should not matter..

they're a bit more expensive than standard typical tubes..






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You can blow them up to a much larger diameter than that of a tire and they should withstand that. When the tube is under water wipe off any bubbles stuck to the tube when you were submerging it. Look whether any bubble springs back to life. Turn the tube to make sure you view all of its submerged surface. Are the valves Schraeder or Presta? If Schraeder you can move your finger over the top of the valve to release air trapped in the outer part of the valve. If that space fills up with air again, the valve is leaking. Internally the valves have thin rubber washers and that rubber can rot. The Schrader valves normally have cores that you can replace and Presta sometimes too. If a valve is leaking and the core cannot be replaced or the leak persists after changing the core, toss the tube.

If a tire holds pressure for 24-48 hrs, it's generally not a puncture. Even a micro-puncture will be almost flat after 24 hrs. Bike tires do lose air over time, and most tires will be basically flat after a month.

Let me put it another way. Most people's longest days are <8 hrs. If it takes two weeks to go flat, you're not going to see a meaningful difference over the course of a ride.

Yeah... that's perfectly normal. I check/inflate my tires, pretty much daily.

I don't know.

Weeks or months later on my bikes, they'll be too soft to ride. Dead flat however, takes the better part of a year.

No solution though, I check my tires every ride. Even the Burley and running stroller. If they keep your prefferpr PSI for 8 hours, you don't have a problem.

My pressure stays up for most of my bikes just fine, if there are no signs of puncture damage I would check the valve to see if it's loose or bad, if the stem sat at an angle for a good while while riding it stem damage is possible...

Or somebody cut them on purpose...

Do yourself a favor, tubes are fairly inexpensive and so are tire liners and adding sealant (commonly called 'slime') when you install the new tubes. Also do not forget to check the inside of the tire itself for rough spots that can damage the tubes.

If the bikes were stored outside the temperature variances may have contributed to the decay of the tubes. Don't forget to check for sun damage to the sidewalls.

true, I did most of that. I brushed some bubbles off that were stuck to the tube but weren't bubbles from leaks. I flipped the tube so the valves were pointing outward and checked both sides of the tubes. No leaks. They are schreader vavles but I didn't press the valve while it was underwater - I thought maybe that could cause a problem but I did do that to one and it didn't leak after.

It's good news that so many of you say it's normal for them to slowly go flat over a few weeks or especially months. I just thought you know, they were air tight. so the air escapes through the actual rubber and/or the o rings on the valve? Doesn't really matter though. Strange though is that I have yard machines with pneumatic tubes that don't seem to go flat over after years. I guess I'll inflate them a bit more though and check psi.

thanks for the input. I'm in NY and it's been really hot heat wave like 95 degrees for days. I didn't know tubes aren't air tight (over weeks/months) and they haven't been inflated since last Fall probably. I just assumed they were flat. And yes they are probably the cheapest thinnest tubes on these cheap bikes.

I did over inflate and put in a bucket or water and paid special attention to the valves but didn't see a single bubble. I would imagine a bucket of water works better than soapy water put on the tube. a lot cleaner too.

As others have mentioned, tubes are porous and let air gradually diffuse through. However the matter is how quickly. More narrow tires will lose air a tad faster than wider - issue of tube surface to volume ratio. In my experience 2 weeks is often enough to make it necessary to replenish air in a healthy tire to keep it pumped up. However, if the tires went flat over such time I would look for some problem. If a tire went flat over few months, something could be wrong, but you would be unlikely to identify the leak releasing so slowly.

You gotta add MORE air 'cuz a slow leak is a SMALL hole...

Keep adding air until you see a bubble when the tube is inflated under water. I had to go ~20-40% PSI of the 'in the tire' pressure and eventually saw one bubble that turned into like 1 bubble / sec. (tube was quite big and starting to balloon a bit)

Since the tube is out of the tire, there is nothing to build up the pressure so it has to ENLARGE

Normal loss of air THRU the rubber will not cause a flat...you gotta a LEAK...

Good luck!

Of course it will.


I've got Latex tubes. They would be flat within a week if I didn't pump them up.