Friday, October 26, 2007

Bicycle Tube Troubleshooting

Those of you who have had more experience with flat bicycle tires might be able to help me out here. I have now patched two tubes this morning and lo and behold -- the patches are in the exact same spot. I am 98% sure both of these tubes originally failed on the Mendota which had it's first flat while riding the KATY Trail. The very small punctures are on the side of the tube.

I've looked at the tire and I thought there might be a very small gash, less than a quarter of an inch -- but now that the tire is on I can't see it for the life of me.

So, here is my theory: If I let the tire pressure get down lower than 30 psi (these tires are supposed to take between 55 & 65 psi) the tube gets partially stuck in the gash and when I get off the bike the tire is pinching a hole in the tube.

My questions:

  • Is this feasible?
  • Should I just make sure I've always got the correct pressure (tough since I don't have a Presta Valve tire gauge) -- or should I get a new tire?


Revrunner said...

I've had a lot of experience patching tubes & replacing tires--far more than I've wanted.

The first thing I would do & which I'm sure you've already done is just to make sure there isn't something still protruding from the punctures in the tire that is puncturing the tube when it's inflated. I guess I wouldn't worry so much about a puncture happening from the other directions--say, from something sticking up from the rim.

If that isn't the problem, then I'd begin to suspect the tube is getting pinched somehow by the tire punctures. You could slip a dollar bill (or something else, if you're too cheap!)between the tube & the tire to protect the tube. Where I'd really begin to suspect a problem is when you're filling your tube to 120+psi, as I do on my road bike. But I wouldn't think pinching would be that much of a problem at lower pressures.

Of course, the surest way to solve the problem, after you get frustrated blowing tubes, is just to replace the tire, which is what I ended up doing. Sure enough, the tubes under 120+psi where simply pressing themselves out through the tiny tire punctures & blowing up.

Noah said...

The tiny gash in the tube is letting you blow the tire out. I always line some easily distinguished marking on the tire up on the drive side with the stem of the valve. This lets me line the tube up with the tire so that once I find the puncture on the tube, it's easy to really, really closely examine the tire casing in the general area where the puncture happened.

If there' ANY protrusion, gash, or similar carnage on the tire casing that's big enough for a tube to herniate into, it's time for a new tire.

You mentioned a little gash, though. You can try booting it with some duct tape, a dollar bill, a candy wrapper or any of those old tricks, but I reserve those tricks for my commute as a last-ditch effort to limp my bike to home, work or a bike shop.

If it's blowing in the same place, my cash is on a small slice. Check everywhere in the are, even on the sidewall. In the case of my trek, an out-of-round wheel was allowing my brake to wear a microscopic hole in the sidewall. After I adjusted the brake, the hole was still there, unbeknownst to me, and allowing my tires to pop.

Fritz said...

I'd vote for the gash/hernia theory too.

Pinching is *more* of a problem at low pressure, BTW.

Like Runner suggests, make sure you don't have a small sharp object still stuck in the tire. Really push down with your fingers in the vicinity of the punctures.

You say the punctures on the side of the tube so this probably isn't it, but also check to ensure your rim tape is adequately covering covering the spokes. Oh, and since it's on the side make sure you don't have any burrs on your rim that might be poking into your tube.

Warren T said...

Thanks for the advice guys. It was 50/50. The Trek did have a sharp piece of what I first thought was bone but now think it must be gravel - stuck in the tire and tube. It may not be the smartest thing to do, but I stuck one patch on the hole in the tire and made sure the patch on the tube was elsewhere when the whole thing went back together. If it works, great. If it doesn't, I'm only out two patches.

Jury is still out on the Mendota. I'll ride the Trek for a while and see if the double patch thing works for me. If I get another flat on the Mendota I'll try to find the gash again and patch it as well.

I wanted both up and running for this weekend because Peter was coming home from school and we wanted to ride the trail in Shawnee Mission Park. His ride home fell through so we're both bummed.