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Tire/tube mysteriously losing air?

Old 12-22-15, 10:19 AM
  #1  
PatrickGSR94
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Tire/tube mysteriously losing air?

The other day I noticed the day after a work commute that my bike's rear 700x25 tire was completely flat. I pumped it back up to 110 psi, and then the next day it was all the way down to about 50 psi. I took the tube out (brand new tube that I put in about a week before), put a little bit of air in it, and listened for leaks. Nothing. Then I filled the kitchen sink with water and checked the tube in water. No bubbles found anywhere. So I dried it off and put it back in the tire, inflate to 110 psi, and back on the bike.

Next day, it's down to 50 again!! The tire is very worn (2 year old Conti GP4S with over 6K miles on it), but that's shouldn't cause such fast air loss. The tube itself was brand new out of the box when I put it on, but I bought the tube probably a year ago and kept it around as a spare.

Is the tube just bad somehow? How could it lose so much air in one day, but not have any bubbles visible when placed underwater?
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Old 12-22-15, 10:33 AM
  #2  
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You may need to put in more air, also make sure the valve is not working. If still no go replace the tube.
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Old 12-22-15, 10:37 AM
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I vote incorrect installation with a pinched tube. Some small leaks simply don't show up under water. You definitely can't hear some small leaks. The only way I've found to identify TINY leaks is to hold it very close to my cheek and feel the air coming out.

Tubes are cheap. Replace it and make sure you install it correctly.

(Personally I'm confused that someone with as many miles on those tires as you have is still asking "tube mysteriously losing air" questions.)
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Old 12-22-15, 10:45 AM
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Inflate the tube until its would be about 2x the nominal size in the tire, at that point any hole is large enough to make noise. Another good trick is to hold the tube very close to your lips. You lips are very sensitive and the extra moisture aids evaporation, so its much more sensitive than the water trick.
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Old 12-22-15, 10:46 AM
  #5  
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My guess would be a tiny piece of radial tire steel cable barely poking through the tire. This is the usual culprit for slow, regular leaks like this.

Pump the loose, removed tube WAY up and then listen/feel for a leak. Also, feel round inside the tire -- what you're feeling for is something that resembles a grain of sand, difficult to distinguish from just molding irregularities, but definitely tangibly different. Chances are, that will be a tiny piece of wire sticking through.
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Old 12-22-15, 10:49 AM
  #6  
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Overfill the tube again, immerse it section by section in water and watch each section very carefully. Sometimes all you get is an occasional bubble at the leak point, not a steady stream, and it can be hard to find.
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Old 12-22-15, 10:59 AM
  #7  
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Also take off the tire and inspect closely for a sharp point of wire or glass. Turn inside out as well. 6K? Just replace both.
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Old 12-22-15, 10:59 AM
  #8  
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Originally Posted by HillRider
Overfill the tube again, immerse it section by section in water and watch each section very carefully. Sometimes all you get is an occasional bubble at the leak point, not a steady stream, and it can be hard to find.
^This.
This was the story with my last two leaks.
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Old 12-22-15, 11:53 AM
  #9  
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Originally Posted by mconlonx
Also, feel round inside the tire -- what you're feeling for is something that resembles a grain of sand, difficult to distinguish from just molding irregularities, but definitely tangibly different.
Try turning the tire inside out and running a cotton ball or microfiber cloth around the inside surface; the fibers will snag on a small irregularity you may miss with your fingers.
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Old 12-22-15, 12:41 PM
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Originally Posted by corrado33
I vote incorrect installation with a pinched tube. Some small leaks simply don't show up under water. You definitely can't hear some small leaks. The only way I've found to identify TINY leaks is to hold it very close to my cheek and feel the air coming out.

Tubes are cheap. Replace it and make sure you install it correctly.

(Personally I'm confused that someone with as many miles on those tires as you have is still asking "tube mysteriously losing air" questions.)
I'm the type of person who doesn't like to waste stuff/money, especially on brand new stuff, and I typically use things until totally worn out such that I can't fix it keep using it. The last tube in this tire had 4 patches on it. The tire was very low one evening after riding home from work, so I chalked it up to just on old, worn out tube. That's when I put in this new one that I'd been keeping on hand as a spare. Yes I checked the tire for debris inside.

If there's a way to make it work, I'd rather make it work and not throw it out. Yes I need a new tire but I've been holding out for Christmas money, plus I haven't had time to get by the LBS, and the other day when I was actually in there I just plain forgot to pick up another tube.
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Old 12-22-15, 12:53 PM
  #11  
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Originally Posted by mconlonx
My guess would be a tiny piece of radial tire steel cable barely poking through the tire. This is the usual culprit for slow, regular leaks like this.

Pump the loose, removed tube WAY up and then listen/feel for a leak. Also, feel round inside the tire -- what you're feeling for is something that resembles a grain of sand, difficult to distinguish from just molding irregularities, but definitely tangibly different. Chances are, that will be a tiny piece of wire sticking through.
This.
Inflate the naked tube until it is firm. You'll be surprised how big it will get, don't worry.
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Old 12-22-15, 12:56 PM
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My hope was/is to find the place of the leak on the tube, which will direct me where to look inside the tire. I was hoping to avoid having to blindly feel around the entire circumference inside the tire if it's something really tiny.
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Old 12-22-15, 01:04 PM
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Originally Posted by PatrickGSR94
My hope was/is to find the place of the leak on the tube, which will direct me where to look inside the tire. I was hoping to avoid having to blindly feel around the entire circumference inside the tire if it's something really tiny.
That's what #dsbrantjr was mentioning, the cotton ball will likely snag on the wire.

Did you pump your tube up till it ballooned up really big? On a really slow leak I'll use half a kitchen sink of water, and I've had to run my hands along the tube a section at a time to get trapped bubbles from the submersion process off. When you watch a bubble grow where nothing was there before, that's a dead giveaway.

BTW, ballpoint pens are a good way to mark slow leaks like this. X or * the site so you don't lose sight of it.
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Old 12-22-15, 01:05 PM
  #14  
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No I didn't get it really big. I'll try it again this evening.
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Old 12-22-15, 01:50 PM
  #15  
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Check the valve too. A couple of months ago a slow leak eluded me, even with the water dunk test, because I omitted dunking the entire valve. Turns out a burr in the rim had nicked the rubber around the Schrader valve stem. That's where the slow leak was. I deburred the rim holes and replaced the tube.

Presta valves may not be as vulnerable to that sort of damage.
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Old 12-22-15, 02:13 PM
  #16  
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Tire should be replaced. It is worn thin, and you will get more and more flats. Unless your time is worth nothing, or you are enjoying this, or you literally don't have $25, it is time for a new tire.

Sometimes a wire embedded in a tire casing will cause a slow leak when it is pressing into the tube, but the tube won't leak when it is out of the tube. So if you insist on using this tire, you need to take the time to search for the wire or other sharp thing. Also check that the rim strip is covering all the spoke ends.

Shortcuts don't work well when fixing flats.

Last edited by jyl; 12-22-15 at 02:18 PM.
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Old 12-22-15, 02:38 PM
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Originally Posted by mconlonx
My guess would be a tiny piece of radial tire steel cable barely poking through the tire. This is the usual culprit for slow, regular leaks like this.

Pump the loose, removed tube WAY up and then listen/feel for a leak. Also, feel round inside the tire -- what you're feeling for is something that resembles a grain of sand, difficult to distinguish from just molding irregularities, but definitely tangibly different. Chances are, that will be a tiny piece of wire sticking through.
+1 I'm guessing there is a reason it is a new tube and this probably caused the problem the first time.
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Old 12-22-15, 03:05 PM
  #18  
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If the tire debris search comes up empty and the valve is secure life Fort Knox. . Then check the rim tape. I once had some metal filing from the spoke drilling work it's way into and through the rim tape, causing a slow regular leak.
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Old 12-22-15, 03:17 PM
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Originally Posted by jyl
Tire should be replaced. It is worn thin, and you will get more and more flats. Unless your time is worth nothing, or you are enjoying this, or you literally don't have $25, it is time for a new tire.
I never noticed a flat rate difference as tires with protection layers (like the GP4000) got thinner. That disappeared when I moved beyond tires lacking aramid layers.

This GP4000S worked as well as new for the first 1037 miles up front followed by 5257 in back.


My current pair of GP4000SII tires with 6025 and 3913 miles are doing well too. Only two punctures come to mind - one where a tube cracked producing a slow leak under a sticker put there by the factory, and a second from a nasty thorn which would have gone through anything short of a Mr. Tuffy.
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Old 12-22-15, 03:26 PM
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Originally Posted by gsa103
Inflate the tube until its would be about 2x the nominal size in the tire, at that point any hole is large enough to make noise. Another good trick is to hold the tube very close to your lips. You lips are very sensitive and the extra moisture aids evaporation, so its much more sensitive than the water trick.

That's the ticket -- the hair in your nose makes a good test kit. Listening can be impossible on a noisy roadway. If at home you can put soapy water over the tube and check for a big bubble.
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Old 12-22-15, 03:30 PM
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Originally Posted by PatrickGSR94
If there's a way to make it work, I'd rather make it work and not throw it out. Yes I need a new tire but I've been holding out for Christmas money
You must value your time at ZERO and you must be DIRT poor in order to think like this AND be holding out for xmas money considering the cost of a new tire.

Tires are cheap, flats are a pain and life is short.
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Old 12-22-15, 03:43 PM
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Some tires are cheap, some tires are not, also all relative to budget. Maybe he plans to splurge on Schwalbe Marathon Supremes?

Anyways, everybody gave good advice above, pump it up more before submerging, slow leaks typically only emit one bubble at a time, and that at high enough pressures to cause the rubber to expand so the hole is "open".

Somebody else mentioned the valve though, I've had situations before where the rubber was cut at the base of the valve (sharp hole in the rim), and out of the tire the tube wouldn't leak air unless you bent the valve sideways to pull the hole open.

Something to check anyways...
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Old 12-22-15, 03:55 PM
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I've never used the GP400o tires. I used to ride Panaracer Pasela Tourguard which have the Aramid layer. After about 3000-4000 miles they were quite worn and would start flatting often (which, to me, is once every few weeks). I would replaced them at that point, and the new tires would flat at the normal rate (for me, once every couple of months).
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Old 12-23-15, 09:35 AM
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What's odd is that I've only had one flat out on the road, ever, in 10,000+ miles, and not on this particular GP 4 Seasons tire. All the other flats I've ever had to deal with have been spontaneous ruptures or slow (fast?) leaks while the bike is just sitting there in the house.

Why do people care what I value my time at? I like tinkering with my bikes, thank you very much, and I'd rather not waste something that is basically brand new with less than 100 miles of use on it, if there's a way to fix it with materials I have on hand (basically a free fix).
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Old 12-23-15, 10:24 AM
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Originally Posted by PatrickGSR94
What's odd is that I've only had one flat out on the road, ever, in 10,000+ miles, and not on this particular GP 4 Seasons tire. All the other flats I've ever had to deal with have been spontaneous ruptures or slow (fast?) leaks while the bike is just sitting there in the house.

Why do people care what I value my time at? I like tinkering with my bikes, thank you very much, and I'd rather not waste something that is basically brand new with less than 100 miles of use on it, if there's a way to fix it with materials I have on hand (basically a free fix).
Which is it? The OP says that the tire is 2 years old with over 6k on it. Now it has less than 100 miles on it?
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