Mystery Flat

[Shoogle]

On Friday I came home and put the bike away. No problems. On Monday morning, I took it out and the rear tyre was totally flat. Pumped it up to its usual 3 bars, then decided to leave it and take the bus as I'd no time to fix a puncture. On Tuesday morning, the pressure was still at 3 bars so I rode it for the rest of the week with no further problems. How could this be? I don't use slime or any other sealants. It's just a normal tyre and tube.

[Eyebrox]

Presta valve not tight initially - then opened and tightened fully when tyre was pumped up?

[Brucey]

some possibilities;

- someone else let the tyre down before
- a patch lifted and then resealed
- valve core was loose before
- presta valve locknut was loose before
- there was as small piece of crud in the valve before and it leaked
- there was water in the valve and it froze and then thawed over the weekend
- valve stem is coming disbonded from the tube and seals at some angles, not others

cheers

[gaz]

.

[Shoogle]

No one else could have let the tyre down. It's in a locked cellar.
It's a new tube - no patches.
I'll check the valve core and the locknut tomorrow.

[JohnW]

No one else could have let the tyre down. It's in a locked cellar.
It's a new tube - no patches.
I'll check the valve core and the locknut tomorrow.

What make was it? Was it a 'Continental' inner tube?

[Shoogle]

Could be. It's either Continental or Schwalbe.

[foxyrider]

Something that Brucey missed that i've observed several times - there is actually a tiny hole in the tube, when the tyre is fully inflated it stays up. Essentially the pressure is sealing the hole but when over time the pressure drops it hits a critical point where the hole opens and then rapidly loses the rest of the air.

[Brucey]

Could be. It's either Continental or Schwalbe.

both usually have removable valve cores, and both have form for supplying their tubes with said cores loose enough that sealing is a bit hit and miss. If you use any kind of pump that screws on then the valve core could easily move.

cheers

[JohnW]

Could be. It's either Continental or Schwalbe.

both usually have removable valve cores, and both have form for supplying their tubes with said cores loose enough that sealing is a bit hit and miss. If you use any kind of pump that screws on then the valve core could easily move.

cheers

I've had that experience with 'Continental' tubes. It puzzled me, but my LBS man was familiar with the phenomenon on 'Continental' tubes. It's easy to tighten the little core with a pair of fine nose pliers - I check every new tube now, and it is surprising how loose the valve cores can be. If the core is not quite fully tightened when first fitted, it's easy to think you have a slow puncture.

A pump that screws on could easily move the core a small amount, as Brucey says, but could equally tighten it when next used and inexplicably 'repair' a puncture without you knowing you've done it.................and it wasn't a puncture after all.

edit 14th Dec - correct word "without" in the last line above replaces the incorrect "with"..................changes the whole sense of the paragraph!

[pwa]

Faced with that problem I would take the tyre and tube off and treat it like a normal puncture, checking the tyre as best I could for penetrating objects. I'd check the tube by overinflating it, possibly using a basin of water to see where the bubbles come from. If all that came up with no result I would put the tyre back on with a new tube and leave the old tube overinflated in my garage to see how it got on.

[JohnW]

Faced with that problem I would take the tyre and tube off and treat it like a normal puncture, checking the tyre as best I could for penetrating objects. I'd check the tube by overinflating it, possibly using a basin of water to see where the bubbles come from. If all that came up with no result I would put the tyre back on with a new tube and leave the old tube overinflated in my garage to see how it got on.

You're right pwa. I'd not come across the phenomenon before. I'll know better in future.

[thirdcrank]

It would be a weird slow puncture that went down intermittently and faster when the bike was parked. Once you have eliminated the possibility of a prankster, I'd back the valve explanations above

[JohnW]

It would be a weird slow puncture that went down intermittently and faster when the bike was parked. Once you have eliminated the possibility of a prankster, I'd back the valve explanations above

A cycling colleague of mine did have that tc. Suspicion fell on a patch, which could lift when the bike was left out in the sun, enough to soften the tyre, but still able to support the tyre for "pump-and-run" to get home. It stayed fully hard after the last "pump-and-run". For a day or two, it stayed inflated, and then when leaned up outside, in the sun, for a run, it went fully down again. On doing the usual testing, the only hole found was under the patch which lifted when inflate out of the tyre.

Subsequently, the 'old guys' in the club said something along the lines of : "Oh Aye - I've known that 'appen"!

[Shoogle]

Didn't use the bike today as it was a bit icy here in Glasgow. Just checked the tyre. Still fully inflated although the valve core was a bit loose. I've had the bike, a 2015 Genesis Longitude with 60mm Big Apples, just under a year and I had my first puncture about a month ago. This was also the first time I've totally failed to patch a tube and I've done a few. It was a tiny hole from a shard of glass. Tried glueless and glued patches, with fresh glue but I still couldn't get them to stick. So, in went the new tube. When I was removing the pump hose from the valve, the core of the valve came out as well. Another first. I've now got a press on pump.