Weird Puncture

[raindog]

Fifteen ks into my ride this afternoon, when my front tyre deflates pretty fast. Inspect inside of tyre for thorns or tacks etc and nothing. So I pump up the tube and it seems ok - can't hear any air escaping or anything, except when I take the pump off, there's a hiss coming from the valve untill I get the little knurled whatsit done up tight. Could the vibration of a very poor road surface have made the knurled thingy come undone? (maybe I hadn't done it up tight in my haste to get out) But even then, there would have to be a fault with the valve for air to come out surely?
Anyway, put everything back and got enough air into the tube to get me home, and I've since banged 100psi into it with the track pump and everything seems ok. Bizzare or what?
Any ideas?

 

[ianrauk]

did you have a dust cap on the valve? May just be a bit of muck and grit.

 

[raindog]

Yes it did have a dust cap. I'm wondering if the vibration of the rough road somehow jiggled the inside of the valve, with it not being screwed up tight, and jammed it in a leaking position.
Just checked and it's still pumped-up hard as a rock. Never had anything like this before. Oh, well, one of life's mysteries.

 

[gaz]

How can the air escape? they are designed so that they have to be open for the air to escape. if you let go then the air pressuire inside the tyre keeps it shut. So i wouldn't expect all the air to come out at once due to this.

 

[raindog]

That's right, in fact at first I thought the spring must have broken or the inside of the valve had fallen apart. But everything seems ok now so that doesn't make sense.

 

[bad boy]

That's right, in fact at first I thought the spring must have broken or the inside of the valve had fallen apart. But everything seems ok now so that doesn't make sense.

I had something similar which I found later to be a small hole by the valve.

check around the valve for any small holes

 

[raindog]

The tyre was still rock hard this morning so I left it as it was. Just got back from a 60 k ride with absolutely no problems, so I'm kind of lost for words. Good job I made this thread or I would've thought I'd dreamt the whole think up.

 

[02GF74]

unusual. swap it over with the rear tube - it is less dangeroous ifthe rear goes.

I would still take it out, pump it up and put into bottle of water to see if it is punctured.

 

[bad boy]

unusual. swap it over with the rear tube - it is less dangeroous ifthe rear goes.

I would still take it out, pump it up and put into bottle of water to see if it is punctured.

Yeah I agree, the fact it went down would bother me, so id have to go through a process of elimination really.

 

[Gary D]

It could be a faulty valve.

The front tyre on my daughters bike goes down very slowly when left in the garage. I got round to checking it today. Took out the tube, pumped it up and checked it in a bowl of water. I had to rotate it twice before I noticed a small air bubble appear around the valve. The knurled nut was screwed down as hard as possible but it still leaks one bubble about every 30 seconds.

Conclusion is a faulty valve with possibly a damaged seat. Remedy is replace the tube or keep pumping it up!!

Gary.

 

[raindog]

It's still pumped-up hard this morning, so I'll leave well alone and see what happens.
I'm convinced that I hadn't tightened the knurled nut up enough and that vibration from the bad road surface shook it even more loose and then it somehow jammed in a slightly open position. It's the only answer I can come up with.
Must say, I've never experienced anything like it in all my years of biking.
Isn't life exciting?

 

[02GF74]

well, I'm still for further investigation or fit to rear or replace.

if you wish to come off your bike should the same happen again, then leave it as is.

there is a reason why the tyre went down, best find what it is to ensure it doesn't happen again.

I had a strange thing once - tyre went down, could find punture, refitted pumped up and was fine but later turned out that there was a tear near the valveand I reckn the way it was seated in the wheel it was possbilel to seal the cut - can't rememebr the exact detials but it was a "tyre down, pump up and was fine" type of situation.

 

[Jonathan M]

Other suggestion: is the threaded post that the little knurled nut screws down on bent? If it is I've had it where unless the little knurled nut is tightened (maybe even overtightened) then the off angle can cause the presta valve to leak.

If is was bent to begin with you may have had a slower deflation, but the roadside repair worsened the problem to the point that you describe.

The only way I can see the loose nut scenario causing air to leak is if the centrifugal force of the spinning wheel can cause the valve to overcome the air pressure in the tube that will be forcing it towards the centre of the wheel????

 

[ASC1951]

The only way I can see the loose nut scenario causing air to leak is if the centrifugal force of the spinning wheel can cause the valve to overcome the air pressure in the tube that will be forcing it towards the centre of the wheel????

It would have to be doing several thousand rpm for that to have any effect, I would have thought.

The most mysterious fault I ever had was on my late lamented Norton Commando. It puttered to a halt after about 50 miles just as if it had run out of petrol. Try to kick start it... no joy. Open filler cap - loads of fuel in the tank. Kick start, whoosh and away we go. 50 miles later the same thing happened again.

I never did work it out for myself. The breather hole in the cap was blocked, so as soon as the fuel dropped enough to create a partial vacuum, everything stopped; but as soon as I had a look, air went back in the tank. I was baffled.

I'm with the others. I would leave it pumped up for a few days, but out of the bike. TBH I wouldn't be too bothered about a sudden catastrophic detonation on the road if you do re-use it - tyres hardly ever do that and in fact I have never had it happen in 30 years.

 

[Jonathan M]

It would have to be doing several thousand rpm for that to have any effect, I would have thought.

That's what I thought too, although I was expecting one of the intellectuals on here to come back with the physics to confirm or rule out this as a likely scenario!!