Mystery puncture

[Andy in Germany]

We've got a bike which keeps losing air from the tyres: so far we've changed the inner tube at least twice, checked the wheel (nothing) and checked the tyre (nothing). Last time the tyre went down within half an hour, this time they held for a week but are now flat again.

Any ideas? we're running out of inner tubes...

 

[ianrauk]

Are the inner tubes punctured? If so, find where the puncture is and look for the corresponding point on the tyre.
Have you checked the rim tape?
Any spokes pushing through the tape?
Are the rims intact?
On the inside of the tyre run some cotton wool around, it will snag on anything unseen that has punctured the tyre ie a tiny piece of glass or wire.

 

[Sharky]

Inflate the inner to a firm but not a silly pressure and leave it overnight or for a few days before you put it back on the bike.
This should eliminate the inner itself as a cause. Also insert inner into a bucket of water and stretch the tube by hand in all directions, looking for the smallest of bubbles escaping.

 

[fossyant]

Rim or tyres causing the issues. Something sharp in there or a shard of metal/thorn in tyres

 

[MichaelW2]

Switch to another tyre and see if you still get a puncture overnight.

 

[Dag Hammar]

A few years ago I bought a new inner tube and the valve itself was faulty. The LBS swapped it for another one without any bother. Have you inflated the tube and held it under water ?

 

[Andy in Germany]

Thanks for the thoughts: we've changed the inner tube twice and chacked tyre and wheel for problems. So far we've found nothing...

 

[ColinJ]

Are the inner tubes punctured? If so, find where the puncture is and look for the corresponding point on the tyre.

Definitely do that.

I had one tube puncture due to a sharp edge on the hole in the rim for the valve . I would never have thought of looking for that sharp edge if I hadn't spotted that the tube had punctured at the base of the valve.

 

[MichaelW2]

Definitely do that.

I had one tube puncture due to a sharp edge on the hole in the rim for the valve . I would never have thought of looking for that sharp edge if I hadn't spotted that the tube had punctured at the base of the valve.

I always check that edge on new wheels and apply some emery paper to round off sharp edges.

 

[ebikeerwidnes]

I had that - tyre would be fine and would ride OK - then next morning it was flat

The tyre was 'puncture resistant' (not Schwalbe) and the rubber was worn down. Somehow a sliver of metal had become embedded in the typre tread - not enough to push through unless there was pressure in it.
Hence, it JUST pocked though at times as ai was riding - but not enough to produce a noticable drop in pressure - but enough to scratch the inner tube and allow a leak to deflate the tyre overnight

Found it by very carefully marking the tyre and tube so that when I found the hole on the tube - which only appeared under pressure - I could trace it back to the exact position on the tyre.
The metal was so embeded it was a right pain to get it out but it has been fine since

After I found that I went over the whole tyre and found another 4 or 5 thorns and bits of metal embeded in other parts of the tread so it looks like the puncture resistance was working!

 

[figbat]

Check one of the punctured tubes for leaks - inflate it until it balloons which will expand any holes and make them more obvious (I can usually find them simply be listening around the tube, but a bowl of water will always find it).

 

[Dogtrousers]

It might be haunted.

 

[presta]

This is the problem with replacing tubes rather than patching them, if you don't find the hole you don't know where you're looking for the debris that caused it. There are plenty of punctures caused by something you won't see or feel until you go rummaging inside the hole in the tyre.

I mark all my tubes with a direction arrow, and all my tyres with a V at the valve, so that once I've found the hole in the tube it's quick and easy to find what caused it.

It's also wasteful throwing tubes away.

 

[All uphill]

Thanks for the thoughts: we've changed the inner tube twice and chacked tyre and wheel for problems. So far we've found nothing...

If your inner tubes are from the same faulty or old batch they could all have valves that leak. I bought a box of ten inner tubes a few years ago for a bargain price; every single one gradually loses pressure over a day or two.

 

[annedonnelly]

Is someone having a laugh and letting the air out at random intervals?