Ngchen

How does one fine the hole for a self-sealing tube that seals at low-pressure (say <=20 psi) but gives whenever one attempts to pump it up with a tire and wheel? The hole is presumably small, but one has to find it to patch it!

Matt Gaunt

Bowl of water.

Grab sections of the tube between your two fists and you should generate enough pressure to force the air out. Under water, you should get the tell-tale stream of bubbles. Good to go with the patch.

prathmann

Or just keep pumping air in with the tube outside the tire. Eventually it will expand enough to make the hole big enough to be obvious. With a really small hole I have sometimes pumped air in until the tube was about 5' in diameter - they can stretch to be very big without any problems. Putting it under water lets you find the hole without so much pumping but is harder to do when you're standing next to a road with no body of water in sight.

Matt Gaunt

Fair point.

200k

Remember that to patch a tube that contains Slime or other liquid tire self sealant you have to, and I mean absolutely HAVE to make sure the surface is clean. If there is the tiniest film of the exuded latex goo on it, the patch will not make a permanent seal! And you may not know it until you pump it up and maybe not until your are riding for a while. Clean it off as much as you can first with a cloth and then sandpaper the hell out of the rubber. If you have thin wall (lightweight) tubes, you're screwed because being that aggressive with the abrasive will tear through, but most likely if you have sealant inside the tube you aren't worried about weight. If you only have the instant patches, I hope you have several because each one will only get you a couple of miles.

Good luck!

200k

Matt Gaunt

I thought the OP meant his tube was self-sealing in that it is a regular tube that doesn't leak air at ~20psi but does when he installs it at usable pressure.

OP - ignore my posts if you have Slime / sealant in there.