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-   -   Can't find the leak (https://www.bikeforums.net/showthread.php?t=1206481)

merlinrkd 07-03-20 12:01 PM

Can't find the leak
 
Feeling dumb about this. Been fixing flats tires for 50+ years but this one isn't getting resolved. Recent 90's Conley MTB. Very clean. Deore components. Came with very recent Kenda tubes and Komfort tires. Am losing 2psi a day out of the rear. Pumped the wheel to 65 psi and submerged it in 6" of water in my laundry utility sink. Don't see any bubbles. Watched it for quite a while. Pulled the tube and pumped it up to about twice the tire size. Not a bubble. I'd like to pump the tube up more. Is there a general rule on how big an unconfined tube can be safely expanded?

Iride01 07-03-20 12:09 PM

Right up until it bursts. I wouldn't worry about 2 psi a day. Although that is a little higher than what I'd consider normal. You check your tires before every ride don't you? I normally expect to put a stroke or two of floor pump in my tires every other day.

hrdknox1 07-03-20 12:25 PM

Could be leaking from the valve core if you didn't submerge that.

JohnDThompson 07-03-20 02:25 PM

I'm with @Iride01; 2psi/day is not enough to get worked up about. If it really bothers you, pull the valve core and pour in some sealant.

Elvo 07-03-20 03:09 PM

2 psi per day is negligible especially if there is a lot of temperature fluctuation in the storage area

tyrion 07-03-20 03:21 PM


Originally Posted by Iride01 (Post 21567320)
Right up until it bursts.

Then back off a couple pumps.

merlinrkd 07-03-20 03:27 PM

The stem was completely under water in the sink. Neve saw a bubble. That was fully inflated inside the tire.

merlinrkd 07-03-20 03:35 PM

This is my grab and run a quick errand bike of the 4 I have. Used sporadically. My 2 road bikes have latex tubes so pumping is a daily deal. The Conley front wheel can go for a couple months. I'm just mystified with my leak detection methods and that 2 psi/day doesn't show a bubble.

tyrion 07-03-20 04:21 PM


Originally Posted by merlinrkd (Post 21567668)
The stem was completely under water in the sink. Neve saw a bubble. That was fully inflated inside the tire.

At 2 psi loss per day the bubble will form very slowly, teeny tiny and pretty much invisible. The bubble will stick to the tube and when it gets large enough it will break away and go upwards.

You can put your hands in and get a death grip on the entire tube, wait for the water to settle and squeeze and you might get an idea of where the leak is. But do you really want to chase this?

Crankycrank 07-03-20 04:32 PM

Also try removing the tube pump it up to big sausage size and stretch a section at a time under water. This makes the hole a little bigger. Also check the base of the stem by wiggling it around under water. Sometimes tears at the base only show up when the stem is moved.

Pop N Wood 07-05-20 07:06 AM

New tubes are $5

tomtomtom123 07-05-20 07:10 AM


Originally Posted by Pop N Wood (Post 21570068)
New tubes are $5

No they're $3.

davidad 07-05-20 09:23 AM

Mount the tire and inflate the tire to at least 50% Above the max pressure on the side wall and submerge the tire. I have used this method and found a thin wire that acted as a plug and deflated the tube when I removed it.

cyccommute 07-05-20 09:55 AM


Originally Posted by merlinrkd (Post 21567308)
Feeling dumb about this. Been fixing flats tires for 50+ years but this one isn't getting resolved. Recent 90's Conley MTB. Very clean. Deore components. Came with very recent Kenda tubes and Komfort tires. Am losing 2psi a day out of the rear. Pumped the wheel to 65 psi and submerged it in 6" of water in my laundry utility sink. Don't see any bubbles. Watched it for quite a while. Pulled the tube and pumped it up to about twice the tire size. Not a bubble. I'd like to pump the tube up more. Is there a general rule on how big an unconfined tube can be safely expanded?

2 psi per day is about the average for the diffusion rate of air out of a bicycle tube. You wonít see bubbles because the air is coming out at the molecular level through the bulk rubber. The diffusion isnít linear so you lose more at higher pressure than at lower pressure. But, generally, I expect to have to pump up bicycle tires on a daily basis.

Bottom line: If the tire goes flat overnight, thatís a puncture. If it only drops a little (<10 psi) overnight, thatís just diffusion and you shouldnít worry about it.

mrrabbit 07-05-20 12:16 PM


Originally Posted by cyccommute (Post 21570291)
2 psi per day is about the average for the diffusion rate of air out of a bicycle tube. You wonít see bubbles because the air is coming out at the molecular level through the bulk rubber. The diffusion isnít linear so you lose more at higher pressure than at lower pressure. But, generally, I expect to have to pump up bicycle tires on a daily basis.

Bottom line: If the tire goes flat overnight, thatís a puncture. If it only drops a little (<10 psi) overnight, thatís just diffusion and you shouldnít worry about it.

You should change your sig:

"Your Daily Dose - Common Sense Rx"

=8-)

dscheidt 07-05-20 05:37 PM


Originally Posted by cyccommute (Post 21570291)
2 psi per day is about the average for the diffusion rate of air out of a bicycle tube. You wonít see bubbles because the air is coming out at the molecular level through the bulk rubber. The diffusion isnít linear so you lose more at higher pressure than at lower pressure. But, generally, I expect to have to pump up bicycle tires on a daily basis.

Bottom line: If the tire goes flat overnight, thatís a puncture. If it only drops a little (<10 psi) overnight, thatís just diffusion and you shouldnít worry about it.

I wouldn't accept a tube that leaks 2 psi overnight on a mountain bike. On a road bike, with skinny tires at 100 psi, I'd exepect that. I run michelin airstop tubes, mostly, my bike with 700X50 tires loses about 2 psi a week (40 psi front, 50 rear). That's checked inside, so temperature isn't an issue. I would expect to be able to find a 2psi overnight leak with leak detection fluid, but maybe not in a sink.

cyccommute 07-05-20 08:53 PM


Originally Posted by dscheidt (Post 21571157)
I wouldn't accept a tube that leaks 2 psi overnight on a mountain bike. On a road bike, with skinny tires at 100 psi, I'd exepect that. I run michelin airstop tubes, mostly, my bike with 700X50 tires loses about 2 psi a week (40 psi front, 50 rear). That's checked inside, so temperature isn't an issue. I would expect to be able to find a 2psi overnight leak with leak detection fluid, but maybe not in a sink.

Thatís why I said that diffusion isnít linear. A mountain bike tire at 40 psi is going to diffuse at a lower rate than the same tire at 60 psi. And the 60 psi wide tire is going to diffuse at a slower rate than narrow road bike tire at 100 psi.

zacster 07-05-20 09:35 PM

2 psi is within the margin of error of most gauges. Why are you even worried about this? I'm happy with a 5psi range.

tFUnK 07-05-20 11:30 PM

Check the valve where the stem meets the tube. Wiggle it around and check for separation.


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