Bicycle Mechanics - patching tubes - emergencies only or tube immortality?
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08-12-10, 09:06 AM
i have a couple of thorn resistant tubes which i love (just thicker rubber) but they're hard to come by locally so i've been trying to patch the punctures. Without luck. Is it because I run the tires at 100psi or my own patching incompetence? I'm certain I've seen other people post about how they never buy new tubes because patching is just as good - are they running mtb tubes at 30 psi?
08-12-10, 09:14 AM
... i've been trying to patch the punctures. Without luck. Is it because I run the tires at 100psi or my own patching incompetence?
Most likely pilot error.:)
I've seen other people post about how they never buy new tubes because patching is just as good - are they running mtb tubes at 30 psi?
I'm running my patched road tubes at over 100 psi. A properly patched tube is as good as a new one.
08-12-10, 09:20 AM
Agreed patching them and running them at 115psi no problems. Are you sanding down the entire area where the patch goes then giving the fluid a few minutes to sit before placing the patch on?
08-12-10, 09:47 AM
immortality. and yes, probably pilot error. keep trying, and try better :D
08-12-10, 10:01 AM
Maybe the thicker tubes don't take as well to patching?
I see patching as tube longevity only, not for emergencies. Patching on the road takes too long, too (potentially) messy, too uncertain. On the road, I inspect the tire/rim at the puncture area for the cause, deal with it as needed, install the spare tube, air up and carry on. Once home, I patch the punctured tube and it becomes my spare. This gives the rubber cement plenty of time to cure. That lasts a few cycles, 'til a tube has 2-3 patches; at that point, I retire the tube at the next puncture. Retired innertube rubber is amazingly handy raw material for MacGuyver projects.
08-12-10, 10:04 AM
Not quite immortality since the tube will eventually have an unpatchable failure - valve failure, hole too close to the valve, split seam, etc. But the patch should hold and be stronger than the tube itself. The main mistake I see when people patch tubes and have the patch fail is that they don't let the glue dry before applying the patch. Put on a thin layer of glue and let it sit until it's no longer tacky - then apply the patch and press it firmly into place. Best to have a spare tube to use while out on the road and then patch the hole after you get home. Put the patched tube in your bike bag so you again have a spare.
08-12-10, 10:17 AM
I don't know from experience but my guess is that thorn resistant tubes would not take as well to patching. The surface is much more rigid than a standard tube, so the patch may not as easily conform and adhere to the surface.
08-12-10, 10:26 AM
Unless the thorn resistant tubes are made from a different kind of rubber you should be able to patch them just as well as any other tube. The big key is to make sure you sand the skin off and expose the darker looking rubber underneath. Perhaps the skin on the thicker tubes is thicker?
OK, OK, it's not a "skin" exactly. But I think that the folks that have good results with patches will confirm that you need to do more than just make a few scratches in the surface. It needs to be well sanded so that the rubber looks "velvet" like before applying the cement.
08-12-10, 11:04 AM
Thorn resistant tubes never patched well. That is one thing I really wish they would stop making and never bring it back. The thickness of the rubber the prep just never held long term vs a std tube, Also valve stem rips in them were more common than std tubes. That is why we always recommended std tube and Mr Tuffy liners. You got the protection people wanted and the ability to patch your way home if needed. Plus the Mr. Tuffy's were reusable. Ditch them and get std tubes.
08-12-10, 12:46 PM
here's another twist - how to deal with a failed patch?
my assumption - tear it off, sand all the cement off, try again.
otherwise i'm waiting to hear if anyone has had good luck patching the thicker thorn resistant tubes. so far they sound a bit troublesome.
08-12-10, 12:53 PM
I have an old wheel and tire hanging in my garage and after I patch a tube I always install it in the wheel and press it up to max. If it's still full after a day or two then I conclude that the patch was perfect. Otherwise I might repatch or chuck it. I have about a 70% success rate, and I wouldn't chuck one just because it had a too many previous patches.
I don't patch on the road unless I've already used the two good tubes in my seat bag and get a third flat (happened twice in 25 years of riding).
I can't think of any reason thicker tubes wouldn't patch as well unless they also have thicker seams that might interfere with the contact.
I used to use self-sealing tubes, and found that they are quite impossible to patch. Now that you mention it, I think I have also had trouble patching thicker tubes. Most tubes can be patched indefinitely, though if you put a patch over a patch, strange things start happening. And of course if you get a hole at/in the valve, that's it for the tube. If the valve itself fails, you may be able to replace it.
08-12-10, 05:55 PM
All tubes have mold release that needs to be sanded off or the patch will release.
08-13-10, 07:18 AM
looks like i fixed another thorn resistant tube on the first try. i'm curious why the other tube would be so troublesome. perhaps because i did a poor job with it before?
I patched a tractor tube (with an appropriate large patch) that are seriously thick and still holds.
On a bike I doubt you cannot patch a tube (any tube), even tubular tires are patchable (but it's time consuming unsewing/cutting open and then sewing it back and sealing the seam)
But the patch should hold and be stronger than the tube itself.
So why don't they just make tubes out of the patch material? :D
08-13-10, 06:35 PM
as has been said before, something like 90% of all flat tires can be patched. If you do really blow out a tube, and leave a huge gash, it might not be repairable. Same thing for damage near the valve stem. Other then that, even pinch flats can be patched if you use a big enough patch, and are sufficiently careful.
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