redbird2

Hello,

For some reason I have not been able to figure out,a front wheel's inner tube lost pressure from about 38 psi to about 20 overnight, after sustaining the 38 pressure without any evident problem during the one 10 mile ride on it just after it had most recently been inflated.

After I had removed the tube from the wheel for inspection and seeing no holes in it, I inflated it while still off the wheel and was unable to cause any loss of pressure or leaking sound despite pumping quite a bit of air into the tube.

Puzzled, but leery of that tube, I installed an entirely different tube onto the wheel, had no problem with this new tube retaining full pressure either during a 10 mile ride or while stored indoors overnight after that.

I have only two potential clues. (1) this is a 700x38c-compatible Presta tube for which I use a Presta-to-Schrader converter. Perhaps somehow the converter, if slightly misadjusted or worn, might enable a slowish loss of pressure out of the Presta valve?

(2) When I removed the first tube, It proved to be surprisingly firmly stuck to the inside of the tire. I did peel the tube apart from the tire without excessive force. Don't know why this clinginess might have occurred, nor why/how it might relate to loss of pressure, but it was odd in and of itself. This tube and tire combination had been purchased at, and installed by, an excellent LBS about 1,100 miles ago. I had previously needed to remove and replace the rear wheel's tube due to an arrowhead shaped piece of glass that had gone through the tire tread and poked a hole in the tube. That rear wheel tube and tire combination had been installed by the same LBS also 1,100 miles ago, and had not been clingy when the tube was pulled out of the tire so as to replace the tube with a new tube. Identical Kenda tubes on F and R, also identical tires on F and R.

Ordinarily this front inner tube had been going about 2 weeks and 100 miles to lose pressure from 38 or 40 down to 30 at which point, or often earlier, I would pump it back up to 40ish.

Any ideas what might have triggered the loss of pressure in that front inner tube?

cny-bikeman

The tube cannot leak without some sort of hole or valve problem. When the tube is outside the tire you cannot inflate to more than a few pounds pressure, so a small leak may not show unless you put the tube under water. It's possible but unlikely that the adapter caused a problem. You could always test that by inflating mounted in a tire) and then simply removing the adapter.

Homebrew01

Some tubes just seem to leak a bit faster than others over time.

Andrew R Stewart 

Tube material is porous. The tiny holes in it are larger then air is. Every tire in your LBS and your house are loosing pressure as I type this. The question is at what rate.

Some tubes are made of a "tighter" batch of "rubber", some of a more porous batch. Some are of thicker wall thickness, some of less wall. Some stretch more to fill the tire's interior volume, some less. Some valves seal better, some less. Some tires start at a higher pressure and therefore have a faster initial rate of loss, some less so.

The solution is to top off your tires at a rate that matches the loss. This isn't rocket science. Andy.

speedy25

Tubes arent supposd to be "porous." Butyl rubber commonly used for tubes isnt supposed to do that. BUT as we well know quality seems to play a part in the leakage rates of different tubes. Some will stay near measured pressure for months and others for days. If one leaks too much, put in another.

-SP

cny-bikeman

The amount of pressure lost, especially when the initial pressure is that low, indicates something more than molecule level porosity. The OP needs to check the tube underwater before we come to other conclusions.

rydabent

The simple fact is that all tubes are porous to a certain extent. Some more than others. The tubes that I have found that lose the least amout of air are Bontragers, but they too still lose air.

RoadTire 

I had a tube last year that kept going soft, then flat after a couple days just sitting. Following the advice of a post I read here on BF somewhere I put a small drop of oil in the valve - never had a problem since.

cny-bikeman

We are talking about a specific instance where the OP's tire lost almost 1/2 it's already low pressure overnight. I have not once seen a tube lose that amount of pressure when I could not find a tube or valve problem.
Do what you wish, but petroleum product can deteriorate rubber over time, so putting some into a valve that has a rubber seal is not a good idea, nor is it necessary.

RoadTire 

oooops. Any other recommendation to keep valves moving when they could be getting gunk from wet salted icky winter rides?

Wanderer

Keep 'em covered**********

rpenmanparker 

Isn't the seal in a Presta valve stem metal on metal?

bikeman715

No , the presta core also have a rubber seal . If you have one with a removable core you will see the seal when you remove one .

cny-bikeman

Nope

AnkleWork

Most likely synthetic rubber, substantially compatible with petroleum. If you're frightened you could use silicone oil instead.

fietsbob

Thicker the rubber in a tube , the longer it retains air, but the heavier it is .. its a trade off ..

Thornresistant innertubes FTW.

RoadTire 

I keep losing the caps, and pretty sure I would be laughed off the trail if I put chain cap-keepers on them ... know what I mean?

Have we solved the OP's issue yet?

HillRider

+1 There is a pin hole somewhere in that tube and an underwater check with the tube inflated firmly is going to be needed to find it. Loosing 18 psi overnight with an initial fill of only 38 psi isn't "normal".

Wash

Dirt in the valve.

You pumped it up, and got a small piece of dirt in the valve, which slowly deflated. It was not enough to notice on the ten mile ride, but enough to notice the next day.

You then deflated the tube which flushed the dirt out, leaving no evidence.

rydabent

bikeman +1

Also if you have a presta with a removable valve, the valve can be slightly loose and pressure will be lost there too.

davidad

Over inflate the tire and submerge it in the bathtub. You should be able to see where the problem is. I fill to about 2 inches and rotate thee wheel until the leak shows up.