Strange Flat - What Happened
 

I went out on a ride today and there is a new subdivision going up on the route. I stupidly decided to spin through it just to see it (lots of construction with the inevitable crap on the road). I hit something (sounded like a strip of metal but I never saw it) and then I heard a gentle, almost soothing "SHHHHHHHHHHHHHH...." as the air left my rear tire (why is it always the rear).

I still ride butyl tubes and after removing the tube I pumped a bit of air into the tube to see where the leak was so I could check the wheel carefully in that area. Couldn't find a leak so I just replaced the tube and rode home (close to the end of the ride anyway).

I pumped the tube up with a good bit of air after getting home and it held air just fine. I forced it into a bucket of water and the only air bubbles that I saw were just a few coming from the presta valve stem - those went away when I closed the valve. I honestly cannot say for sure that the valve was closed on the ride. I don't know if this tube will hold 90 pounds of air when encased in a Conti tire, but it certainly holds low pressure just fine.

So either this tube has a high pressure only leak (it was DEAD FLAT) when I removed the tube, or something funky happened regarding the valve/stem. No big deal other than I would prefer to fix and reuse the tube. I just have no idea what to fix.

Thoughts on what happened here? Thanks.

dave

Do you have a pump that screws on the valve? Some tubes have a removable valve that may get loosened when you remove the pump. Maybe it was borderline and hitting the bump pushed it over the edge. I'd be curious to see if it holds air when you mount it with a tire and pump it up to full pressure.

I have a 'normal' lever type pump that I used (both floor model and the mini on my bike).

I guess that I will experiment putting that tire back on some wheel. But I also play classical guitar and changing a tire is not compatible with good guitar nails. This event ended up tearing my 'c' fingernail off at the base. It will take a couple months to grow that one back. But I might try the tire swap anyway.

dave

I ran into that with a batch of Conti tubes. They were just loose enough that they were fine until you unscrewed CO2 during a ride. Not obvious.

That is interesting. This one is a 'CST' tube. I wonder if they make tubes for Conti?

dave

I carry a valve tool on rides/to races. It's light, compact and a lifesaver. I'd try tightening up the valve core as much as possible (without shearing the valve off the tube) and trying again. Also, if your valve is particularly old or maybe grimy, it could have grit lodged in it that keeps it from "closing" all the way?? Though that seems unlikely in this case. Curious as well. If the tube ends up with a slow leak, you can throw in some orange sealant and it should take care that.

On two occasions I've had flats that were tricky to track down. Eventually, I found the problem was at the stem itself. Nowadays I check new tubes but inflating them before entering service and hang them over a door overnight to see if they hold air.

It's typically the rear because the debris (that was lying flat) gets kicked up by the front tire and is still flopping around when the rear passes over it.

I've had a very slow leak (from a tiny piece of wire). I had to submerge the inflated tube in the bathtub, then go around it and wipe off the small attached bubbles with my fingers. At the puncture, a small new bubble would form in 15 or 20 seconds, very slow. I then wipe it off and see that another new bubble appears there. It's hard to find. This would be too slow to make a "shhhhh" hissing noise while on the bike, though.

Most punctures can be found by holding the inflated tube up to your cheek, you can feel and/or hear the air leaking. Or they spit out a stream of bubbles under water.

Sometimes the seal at the base of the stem tears. Try the water test and move the stem around some.

How could it be a "high pressure only leak" when the tire was "dead flat"? At some point, low pressure air leaked out, right?

I've had a couple of tubes that kept going flat, with no bubbles in the bucket, but I just tossed the tube rather than spend time on it. I think it had to be the stem though.

I have decided that this pretty much had to be a stem/valve problem.

In retrospect I probably could have just put air in the tire and continued on the ride - an irritating thought.

dave

one time I was about 2 miles from home on my 17 mile commute & I heard the front tire start leaking air. eyeballed a cozy grassy spot next to a church to swap the tube. as I approached the grassy spot, the leaking air sound stopped. the tire was pretty soft but I wasn't riding the rim. wound up taking out the tube which had plenty of air in it. no sign of debris or tube damage. put a new tube in, rode home & trashed the old tube. God works in mysterious ways ...