What would cause a no-puncture flat?

[Captain Zep]

Out on a wee Sunday morning loop this morning I stopped at roadworks for a few seconds.  Just as I started to pull-away again, I thought Uh-Oh.  Sure enough, my front tyre was flat.

Note to self:  All the spare tubes in the world in your saddlebag won't do you any good if you've forgotten to bring a pump! 

When I got home (SWMBO collected me in the car), I found that the tyre wasn't completely flat (but nearly).  I pumped the tyre back up to 100psi, and it seems to be holding nicely. 

How would that happen?  Any time I've had a puncture before, it's been pretty sudden deflation or an out-and-out explosion.

[CathH]

Dodgy valve? I suffer from valves not closing properly quite a lot because of the Slime in my tubes.  Little bits of fibre are always needing to be blown out.  I've got a little water dropper standing by every time I pump up my tyres to check for air leakage.

[Fixedwheelnut]

 sticky leaking valve? especially if it wasn't tightened down

[clarion]

Specialized tubes have valves made of cheese.

[Crumbling Nick]

What did the underwater bubble test reveal?

[Captain Zep]

Thanks chaps.  I Hadn't thought of checking the valve.  

RJMcB

[andygates]

Traffic light goblin.  You need to propitiate them - solstices are good, they seem to like cakes and milk.

[Biggsy]

A puncture can be so small that the tyre takes many hours to go down.  Check for tiny bubbles under water.

Also give the valve a yank to test the bonding between valve and tube.

I've never had a Presta valve fail (when closed).

[orienteer]

Have had a Presta valve leak: Continental tubes have a removable core which unscrews, it has to be tight.

[kyuss]

I had a similar thing happen last week. Tyre went down slowly on the way to work so pumped it back up hoping to get to the office before it went flat again and it held for the rest of the day. Checked it out when I got home and seen that it was a thorn that caused it. Pumping it back up and riding to work pushed the thorn in a little further in which sealed the hole it created.

[julianbramley]

What if the outside air pressure massively increased, it would appear flat then?
Maybe you've been in a compression chamber?

[mike]

or been quite deep underwater, perhaps?

[Captain Zep]

Thanks for the replies folks.

Finally got around to checking the leaking tube today.  It's got a puncture from a strange bit on the tube:



The lozenge shape is cut in to the tube, and is leaking from around it.  Is this damage from the factory?  I've no idea what the brand is - they were on the bike from new (150km ago).

RJMcB

[border-rider]

That's been stamped out/cut in

If it's on the inside circumference, is there anything that shape on the rim ?

Otherwise, has it been trod on with a sharp thing under it ?

[TimO]

That's kind of weird, I've been sitting here trying to think of how you could get a shape like that in a tube on the bike, or even if somehow abusing it when putting the tyre on/off.  I can't come up with anything, so maybe somebody with a better imagination than me can make a suggestion.

If it was me, I'd go back to the shop and complain, if that shape was somehow marked into the tube, it would be an obvious failure point.

[Captain Zep]

That's been stamped out/cut in

I agree, it's a very regular shape

If it's on the inside circumference, is there anything that shape on the rim ?

It's on the tyre side

Otherwise, has it been trod on with a sharp thing under it ?

Not by me anyway.

When I blow up the tube a bit (outside the tyre / rim) (this mark is v. hard to see unless the tube is inflated a bit).  The shape of the tube is very irregular i.e. very fat at some points and narrow at others. 

I've found the brand on it "Innova Made in China"    Back to Monsieur Michelin for me.

[Jurek]

At a guess I'd say your lozenge shape is the witness mark from one of, possibly several, ejector pins on the inner tube mould tool.

Once the mould cavity has been filled with latex / butyl / whatever the tube material is, the ejector pin / lozenge will push the tube off the mould as soon as it has had sufficient time to cure / cool, allowing for the next charge of the tool to be introduced.

Speeding up this procedure (pushing them off before they've fully cured / cooled) allows the manufacturer to churn out more units per hour.
It is possible the ejector pin is pushing against a product which hasn't fully cured / cooled. Creating a weak point on its sharp edges, causing perforation(s) to take place there, especially once under pressure.


Purely supposition on my part - until that is, someone with a better knowledge of injection moulding corrects me.