Mystery deflation

[Notsototalnewbie]

My mum has an old MTB that she took to Halfords for a service (not being close to a decent LBS - or at least not one she wants to cycle to) and they've put a new tube in.

After a couple of weeks it went down, completely flat. I took it out when I was there, had a good look, could find nothing wrong, put it back and pumped it up. Three weeks later, completely flat again.

So I've had it out again, pumped up and in a bath of water to look for bubbles, particularly the valve in case it was leaking. But no bubbles were forthcoming even though I held it under for quite a while squeezing the tube.

Are Halfords tubes just crap? All I can think of is that the valve is very slowly leaking air and she should get a new tube.

(NB she lives in Aldwick nr Bognor, and as I'm here for the bank hol, I suggested we both cycle to Chichester to a decent LBS to get new tubes, but she said Chichester was too far  )

[TimO]

If I had to guess I'd say that there was a very very very small leak from the valve (a leak in the tyre itself will probably get progressively bigger).  Possibly so small and slow that it won't be visible in the water unless you wait an awful long time for a bubble to form.

Change the tyre for another one, even good brands of tyres will occasionally have a bad'un.

Alternatively, are next doors kids jumping over the wall and letting it down periodically!

[Notsototalnewbie]

Yep, that's what I thought.

It's locked in the garage so no pesky kids hopefully!

She doesn't want to cycle the 6 miles to a decent LBS though. Maybe if I let her have a rest in the middle 

[Zoidburg]

If I had to guess I'd say that there was a very very very small leak from the valve (a leak in the tyre itself will probably get progressively bigger).  Possibly so small and slow that it won't be visible in the water unless you wait an awful long time for a bubble to form.

Change the tyre for another one, even good brands of tyres will occasionally have a bad'un.

Alternatively, are next doors kids jumping over the wall and letting it down periodically!

Correcta mundo

I have had a few customers come back to the recyling project with flats over and over again

Me - "Do you leave it locked up outside in the same place every day?"

Customer - "errrr...yes why?"

Me - "someone is letting your tyres down, would you care to buy a pump?"

Its like watching a light come on in there head

[Biggsy]

I've used a countless number of inner tubes in my life, but never had a leaking Presta or Schrader valve - so I think that's rare.  I mean the actual valve rather than the bonding between valve and tube.  It's common for there to be a split there, that can be revealed by waggling the valve.

Most likely is a small hole elsewhere in the tube that you've missed.  These can be so tiny that it won't release the usual stream of bubbles under water.  Instead you'll just see a static little bubble.  You have to wipe off all the bubbles from the air that sticks to the tube from the outside when dunking in water to eliminate them, and wait a few seconds for a new bubble to form with every section you check.  And check all round the tube, not just the side that faces the tyre.

Though I am sad/tight enough to check tubes this thoroughly myself, I wouldn't blame anyone for just replacing the tube instead.