Thanks all - before anyone gets excited I've still not found the cause!
I presuming the offending tyre/tube is still on the wheel on the bike. These are only small wheels. You could get a washing up bowl, fill to brim and then dip the wheel into this and rotate it. Alternatively take the wheel out, fill kitchen sink with water and rotate the wheel in there.
Nup; off the bike now and all in bits although it doesn't take long to put it all back together again. Seems we don't have any washing up bowls but I did reassemble and hold the wheel assy horizonal under the tap, running water onto the bead and allowing that to run around the entire circumference of the wheel on either side, with absolutely no bubbles. Likewise none at any of the spoke holes under running water either.
You probably only put a very low pressure** in the tube outside of the tyre. Maybe the hole is so tiny that it takes more that to open it up?
** PS I just tested my idea on a spare 25C tube. I pumped it until it was ballooning up (bigger than I would normally inflate it to test for leaks) and the pressure there was only 10 PSI!
My suggestion is to really stretch the tube where it is under water. If it is just a tiny hole, maybe that will open it enough for bubbles to form?
Yes, and thanks for trying yours! I was thinking about this whilst on on (another) bike earlier; although if anything I'd expect the tube to leak more when inflated unconstrained as the material obviously stretches and it would figure that this would open up any existing holes / make the leak more obvious.
I'm not sure I've ever had a problem finding leaks, even tiny ones when inflating the tube off-wheel and holding it under water in sections (as I've done with this one already).
Maybe it's leaking from the valve? - has 'only the tube' been tested?
This crossed my mind when I was out and would make sense if it's pressure-dependent and inflating off-wheel doesn't reach the pressure at which it leaks. Sadly however the whole lot has since been back together, inflated and the valve tested for leaks with water - with absolutely no indication that any air is escaping.
It could be intermittent however, so I've stripped and cleaned the valve just in case.
Tiny holes can be hard to find. Try a cloth with loads of washing up liquid on. Pop air in tube, rub cloth over tube and hopefully you'll see some bubbles.
I'm not really convinced the rubber is necessarily leaking though, since there were no bubbles when it was held under water and it's evidently held pressure while left inflated on the kitchen table for the past 3hrs I've been out.
Inflate the tube and run it slowly past your lips. You should feel the leak that way. Rotate it as you go in case you have your thumb over the leak.
Ta but again, I don't think this will detect anything that immersing it in sections in a pan - as has already done - wouldn't..
Throw the tube away. Life's too short.
Crikey - don't let any of your fellow northerners hear you talking like that!
As it happens I'm too tight, hate waste, hate being beaten by inanimate objects while binning it would leave me with no (immediate) spare to carry on the bike.
It's all back together and sat with the pump attached, with no indication it's losing pressure. I'll leave it while I do the million other things I need to get done today, if it's still behaving I'll remove the pump and repeat - at least if it failed then this would indicate the valve...
It's bizarre as it's been on the bike for the past week or so with no issues and has only started behaving like this once it was removed during the tyre swap..
