Some advice and a lot of first-hand anecdotes and observations from someone who accidentally had a career in the bike business.
Perhaps, if you put a little baby-powder in the tube you may find the mysterious leaks. I have used this technique to quickly fix flats on the road side, It makes finding the cause and the actual leak quick and obvious but requires thorough cleanup before patching =)
John, This sounds very interesting. But I am sure I am missing something central here. How, pray tell, does one put baby powder IN a tube? And once this is done, how does it help finding the leak. Please elaborate.Leo
To put something in the tube, remove the valve core. I have had several of these over the years. the culprit almost always ends up being a tiny hole right near the valve stem. These will cause flats one of two ways: 1. They leak slowly over time and eventually flat overnight. 2. You notice the tire getting soft and pump it up, they fail catastrophically. I have been a witness to this in my office, where a tire I inflated before riding in suddenly goes around noon. I went crazy trying to figure out the cause of these. My valve holes in my rims were nice and smooth, rim tape was in the right place, etc, etc. I did recently read some advice that you should inflate partially, then deflate and make sure the tube is always down in the rim bed. The hypothesis is that you can have the tube too high in the rim, and the threading of the stem will hold it there as you inflate, creating a void in the rim bed that the tube then overstretches to fill, and eventually you get a little failure there, adjacent to the valve stem. I'll be testing this shortly. I put on new tires last night and one one of them, when I followed this procedure, I distinctly felt the tube "pop" back down into the rim bed when i let a little air out. So we'll see if I can avoid another mystery puncture.
I've never tried the baby powder trick. I either fill a sink with water and submerge the tube and look for bubbles, or wash my hands (getting them good and lathered up) and run my soapy hands around the tube and look for bubbles that way.But, yeah, it's usually a crappy valve stem joint to the tube.Wolf.
If you have Presta tubes, never use the "stem ripper" nuts. Just throw them away or keep a few for improvised projects. The threading is the same as on most brake hardware.
I've only done this with my schrader tubes but it should work about the same with presta valves. Remove the core, roll up the tube, place empty stem into a small pile of the powder. When the tube unrolls it creates a vacuum sucking the powder in. do this a couple times to ensure enough powder is in tube. Replace core and remount everything. When you get a flat powder escapes with the air highlighting hole in tube and cause of the hole.=)
I've had pretty good luck with Slime - I don't know what leaks it may have fixed for me entirely, but I have had several occasions where it slowed a leak enough that I was able to get home on a gradually-softening tire rather than having to fix it by the roadside. (Schrader only - I've never tried to get Slime through a Presta, nor have I tried the pre-Slimed Presta tubes that REI and others sell.)And with Slime in the tube, it's generally not difficult to locate leaks. (Now, patching them becomes a different story... )ymmv,- MA commuter
I absolutely despise Slime.I charge extra to fix flats where Slime has been used, because of the mess it adds to the process. I've been shot in the face too many times as I let the residual air out of a tube in which Slime has failed, which it seems to do more often than not.
Nice to know it's not just me who has the odd tube that leaks in use but not once set free. I'm guessing pressure on the valve/tube interface opens up a tiny leak that is better sealed when the tube is unencumbered
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