Cycling UK Forum

I picked up a slow p******* on the tandem last Monday. Not drastic - the tyre softened but we got home OK without having to fiddle at the side of the road. I took out the tube yesterday, but try as I may I couldn't find a leak in the tube. However, knowing there was one, I persevered by rotating the tube under the water more and more slowly. Eventually I saw a small (very small) bubble emerge at a rate of one per 5 seconds. Slow p******* indeed.

BUT - the escaping air wasn't from the tube itself. It was coming from between the valve stem and the valve core (presta valve). I've never come across this before, not least because I've never had a need to take a valve core out of a presta valve stem (not so from a schraeder). The solution was a slight tweak of the core with a pair of pliers, and Bob is now my uncle.

Is this a rare occurrence?

I have an inner tube with an undetectable p******e. I pumped it up twice in a week, and it lost pressure. Since removing it from the wheel about three weeks ago and pumping it up, it its remained inflated ever since.
Am I going to reuse it…err no, but it is curious.

Geoff.D wrote:Is this a rare occurrence?

It's happened to me and like yours it took a great deal of tracking down before the fault was found.

The exact same thing happened to me a couple of weeks ago - on a tube on the bike and on the spare tube (which was well used). I can only guess if the the valve locknut has been opened a few times (and maybe the cap done up and undone) perhaps it slightly loosens the valve core.

Whatever the cause it had me stumped for about a week. I only found it by inflating the tube mounted in the tyre on the rim to ~100psi and dunking the whole wheel in a big tub of water. At that pressure the leak was obvious whereas checking the tube inflated outside the tyre there was no sign of a leak on the valve at all.

Cue for someone to tell you the wheel will now fall apart AM7 !!

I've had the same thing happen a few times - the valve is now my number 1 suspect for any flat tyres at home.

Having had it happen in the past,I now tighten valve cores on new inner tubes before fitting.

I have had this happen a couple of times.
I think it is down to my track pump head gripping and undoing the valve core slightly whilst being removed.