Slow Leak Venting...
 

In the morning when I go out to the shed to choose a bike for my ride to the office, I'll pinch the tires of the other two bikes (plus my wife's bike) to see how they're doing.

Earlier this year my old road bike's front tire had a slow leak. Every few days it would be too low to ride, and after a week or so it would be flat. After finally pulling the innertube and inspecting it, including dunking it in water, it turned out the removable core of the presta valve was loose. I tightened it. problem solved.

Months passed, and all was good.

So four days ago I decided to take my old road bike out for a spin. This time the BACK tire was completely flat. Hmmm. I inspected the outside of the tire and saw no breeches or intrusions. It was a non-removable core valve, so that wasn't it. I pumped it up and rode for an hour. Came home and it was fine.

Monday morning it was flat again.

So I pumped it up and rode it to work today. It was fine after the 40 minute ride in. At lunch it was down from 95psi to 60. So I pulled the tube, pumped it up to 20psi and inspected it.

Didn't hear anyting. Didn't see anything. Wet my lips and ran thetube past them...didn't feel anything.

So I filled a sink and ran the tube through the water. Just as I was about to get all the way around I saw the tiniest of bubbles. Aha!

I looked and sure enough, there was a thin wire sticking in the tube. I squeezed the tube and a couple of more small bubbles came out, plus one from a few inches away at the seam. I squeezed the tube harder and circulated it around the water in the sink and more more tiny, tiny bubble began leaving the tube at various points along the seam.

Death by a thousand bubbles.

I tossed the tube and replaced it with a (hopefully) fresh one, then rode to the local bike shop to buy a new tube to put in my saddlebag.

Loose valve cores and failing seams make me wish for the simplicity of catastrophic blowouts, or at least large, easy to find punctures.

I'd even settle for snake-bites or pinch flats.

Slow leaks

I hate them.

I'll take a leak that allows you to pump up and ride home over a blowout any day. Much easier to work on the bike in the comfort of the garage than on the side of the road.

I've had a few weak seams with the thinner tubes. Thicker tubes can add noticeable rotational weight.

I only use Schrader valves, and never had a problem. I realise they're not as aerodynamic though..

Try having it happen while you’re out on an unsupported tour. During one of my cross PA tours I awoke to a flat. Couldn’t find the leak for the longest time. Finally had to run the tube through a puddle left behind by the rain the day before. Found the tiniest whole I have ever seen. Also found the little piece of wire in the tire that had caused it.

Sounds like a candidate for sealant.

Sometimes the culprit can be a problem with the valve seat. It can deteriorate, and not be completely airtight, or it can get a bit of gunk stuck to it and cause it to not seat properly.

SB's lesson on tubes and valves -- https://www.sheldonbrown.com/inner-tubes.html#valves

Dan

Tubes have only one seam, where the two ends are joined together. What you are probably referring to is a flash line created during the vulcanizing process. This flashing has no inherent weakness and thus does not fail. What you observed were probably small air bubbles from the original wire puncture migrating along the flashing line until large enough to become visible. I'd predict that if you had repaired the original wire puncture, the tube would have been just fine.

I think you may be right.

On the other hand I felt the need to vent, and my AirZound air horns are out on the bikes in the shed.;)

I went Mavic USTs.