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The flat that won't go away - tube splits open without visible cause

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The flat that won't go away - tube splits open without visible cause

Old 08-29-10, 06:11 PM
  #1  
christofoo
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The flat that won't go away - tube splits open without visible cause

This has happened twice consecutively, and it just doesn't make sense to me.

I put in a new tube, pump it up, ride it around, put it in the garage overnight, in the morning it's flat, and the tube has a split facing dead center on the rim. The second time this happens the location is different, I tried using baby powder to lube the tube, but it happened anyway.

The split is about a centimeter long, there are no signs of cutting or wear or any weakness in the tube. The direction of the split is lengthwise, or if you prefer in the plane of the wheel.

I will say that I have an extremely narrow rim. The tires are 25mm 700c, and the rim is even a bit narrow for that size (although that is the stock config for this bike, Windsor Wellington). I inflate to 110 PSI. The rim is covered with Velox, and like I said there are no signs of cutting or wear.
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Old 08-29-10, 06:15 PM
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Now that I hear myself describe this, I wonder if it's because I put too much air in the tube before I put it on the rim. (I've been inflating it inside the tire a bit and then putting the tube and tire on the rim together.) Does that make sense to anyone besides myself?
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Old 08-29-10, 06:31 PM
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I think a split of that size is often caused during the mounting but there are other possibilities. I find that the right amount of air to use during mounting is equal to what I can blow into the tube with my mouth (700 x 23c). If the split is on the rim side of the tube this makes me wonder about the rim strip or tape. I use Velox rim tap on all of my rims. I mount one tire bead, add the slight amount of air, mount the tube, then mount the other tire bead. I have to use tire levers and exercise extreme care with the levers.
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Old 08-29-10, 07:17 PM
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Often that is a symptom of having a little tube caught between the bead of the tire and the wheel itself. In fact the exact symptoms you describe are very common with this problem.

The way to check for this is to inflate the tire part way and look at the edge of the tire next to the rim all the way around on both sides. If there is one section that is not as well seated as the rest, it might be the tube pinched in between the tire bead and the rim. If there is a place where this occurs deflate the tire and see it any tube is pinched in there. Before each inflation with only a very little air in the tube go all the way around each side of the rim and push the tire in gently to see if there is any tube pinched between the tire bead and the rim.

Also if you are installing with tire levers be very careful. Most tires can be installed without them, roll the bead over the edge of the rim with both thumbs at the tight spot don't just push it.
I also inflate the tube just a little to get it up in the tire away from the bead. If you are new at changing tires ask a shop to show you what I mean about rolling the bead over the rim.
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Old 08-29-10, 07:41 PM
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+1 Lengthwise split = Pinch flat. I usually put some air in the tube to make sure I don't have it twisted or kinked, then let out almost all of it, prior to mounting the second bead. It has worked well for installing about 200 tubes in the last two years.

+1 If at all possible (and usually it is), I roll the bead on, and avoid using tire irons.

+1 Once installed, I will push the bead inward to make sure there is no tube showing under the bead.
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Old 08-29-10, 09:27 PM
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I'm aware of pinching the tube around the bead, and I really don't think that's happening. The tear is occurring right dead center on the middle of the rim. Plus I'm quite careful about how I put the tube in. The amount of care I'm putting into this is getting ridiculous. I've spent an hour today and never got passed 20 PSI... as follows:

I'm trying to pre-inflate properly now, and I'm reminded there is a reason why I started pre-inflating too much. It feels like the tire is too short, i.e. when I get to 5 PSI the tube has not filled out the tire in all places. Remember this rim is really narrow, what it feels like is the tube is being held in the rim/bead area by friction (I swear it isn't twisted or pinched, I am very careful), this causes the tube to stretch a great deal to fill out the tire. Before I had my current problem I had a tube tear on the other side, it felt just like this before I inflated it. (The tear was violent, a very loud pop.)

I'm at a loss here. It seems like 28mm tubes would fit a lot better. (I'm using two types of tubes, one is the nashbar 700x19-26 presta.)

I just can't believe changing a tube can be so hard. I design lasers for a living but this is making me feel like a moron.

Last edited by christofoo; 08-29-10 at 10:37 PM.
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Old 08-29-10, 09:36 PM
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Maybe run your finger all the way around the rim tape to feel for sharp edges. Also check the tube is not punctured before install - inflate it, let it sit overnight and deflate before installing into the tire.

Can you determine from the 2 punctured tubes whether they are at the same spot relative to the valve?
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Old 08-29-10, 09:51 PM
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Try to picture this in your mind and see if it leads you to a solution.

The airspace inside a mounted tire is sort of hourglass shape with the main chamber inside the tire, and a smaller one inside the rim. On narrow rims, the neck between the two chambers can be verrow narrow.

When you fill the tube, it forms a sausage and fills the space in the tire, then with more pressure, the section across the bottom then blows down into the tire stretching even more and possibly going beyond what the tube can take. There's little you can do, but here are some ideas that might help.

1- buy good quality tubes, and get the largest that's smaller than the tire, ie. for a 700x25c, look for a 23-25mm tube vs. a 20-25 tube if possible.
2- powder both the tube and the tire well, especially down near the inside of the bead.
3- inflate slowly, and while the tire is still soft enough massage it a bit to help the tube shift and equalize. This may not actually do anything, but it can't hurt.

IMO the key issue is tube quality. Better tubes stretch better and are less likely to split from the hyper-stretch.
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Old 08-29-10, 10:26 PM
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FBinNY - beautifully said. How do you shop for tube quality? I don't remember the brand on the first one, it was from the LBS, the second one was Nashbar. I've really had three tears now, one on the top of the hourglass, two on the bottom, it feels a bit like whack-a-mole.

I put air into it just now, we'll see if it causes me more trouble.
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Old 08-29-10, 10:56 PM
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Shopping for quality in the tube world is tough, since almost are house brands and you don't know who made them.

I try to find tubes with the actual makers brand name, like IRC or Kenda. The problem with house brands is that nobody cares about quality. The maker doesn't because it isn't his reputation on the line, and the buyers for house brands shop around for the lowest cost. Once you find a tube that works better, try to stay with them. You might also try to find slightly thicker walled tubes, even though they weigh more.
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Old 08-30-10, 12:47 AM
  #11  
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Originally Posted by christofoo View Post
FBinNY - beautifully said. How do you shop for tube quality? I don't remember the brand on the first one, it was from the LBS, the second one was Nashbar. I've really had three tears now, one on the top of the hourglass, two on the bottom, it feels a bit like whack-a-mole.

I put air into it just now, we'll see if it causes me more trouble.
Schwalbe tubes are of the highest quality. They inflate and inspect each one individually before packaging. The rubber's a tiny bit thicker, higher quality rubber, higher quality valve. If you install one, and this happens again, you have definitely eliminated a faulty tube as the culprit.
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Old 08-30-10, 08:08 AM
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When there is a few psi in the tube and the tire is fully mounted, do you carefully push the tire towards the center of the wheel, and look into the gap all the way around on both sides, to see if there is no tube pinched between the tire bead and the wheel before inflating more?

Do you use tire levers?

Have you repaired a lot of flats before?
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Old 08-30-10, 09:16 AM
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Bummer, the third attempt is the same flat. It never happens right away, I have to wait overnight to see if it happens.

I'll follow that inspection routine next time, but I still don't think that's it. I don't use tire levers on this wheel and I feel my way around. I don't think pinching the tube in the beads is incredibly subtle. (You disagree?)

In my lifetime I've repaired at least 50 flats and never had this problem on, say 27x1-1/4" wheels. But I have never used super narrow 23mm rims/tires until this year. The first time I fixed a flat on this bike, I patched the tube that came with the bike, and succeeded. On the second flat I used an LBS tube and it tore, someone gave me a 28mm tube and a buddy installed it and succeeded. This is the third flat, the tube that came with the bike has a small valve tear that can't be fixed, I've put 3-4 hours into it with 2 tubes (1 attempt with a new Nashbar tube and 2 patched attempts) and had exactly the same result every time. I'm at a point where I don't have any tubes on hand which I can trust.
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Old 08-30-10, 03:22 PM
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Perhaps this may be a good time to bring it to your LBS to install it for you. It'll cost you more in busted tubes than the labor for them to do it. Many LBS's even have a flat guarantee (usually less than a week) that they will replace it free of charge if there was a problem with their install (few have a puncture free guarantee)

Long splits usually indicate a failure in the mounting process. I replace about 5-20 flats a day as an LBS mechanic and this is my method:

Remove tire and tube, making note of mounting location of tire in relation to valve hole.
Inflate busted tube to find puncture type and location (pinch, puncture, or rip and rim, sidewall, or tread)
Inspect wheel or tire near location of puncture (often a thorn, staple, or exposed spoke head can be found that would repuncture)
Partially inflate replacement tube (or patched tube) so that it is sufficiently rounded and inflated.
Locate the valve stem and insert the tube into the tire so that the valve lines up with a brand marking on the tire.
Insert the remainder of the tube into the tire. If tube must be bent to fit in, deflate tube until whole tube can be inserted without a bend or wrinkle.
Run fingers along the inside of the tire between bead and tube to ensure no snagging
Insert valve stem into valve whole on wheel with one side bead side inside the rim area and the other outside.
Secure the inserted bead around the rest of the wheel by moving both hands away from the valve stem evenly across from each other
At the valve stem area, insert the remaining bead into the rim
Secure the remainder of the bead by the same method, both hands spreading away from the center of the wheel around the outside.

The last bit of the second bead is always the hardest, especially on road tires. Avoid using tools for installation if possible (unless they are specifically designed to mount tires...NO SCREWDRIVERS!). Sometimes deflating some additional air (even as far as all of the air) may be necessary. If deflation is needed, be very thorough about keeping the tube completely enclosed in the tire and not snared anywhere between the bead and rim.
Inflate to ~20-30psi and check for any bulging or unset bead and correct accordingly (deflating the tube some is usually the best way)
Finish inflating
Ride!
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Old 03-03-11, 05:10 PM
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I added many layers of tape over the top of the Velox rim tape, and haven't had this problem since. I think the Velox adhered just fine to the bottom of the valley in my rim, but it wasn't uniform around the sides of the valley. Maybe it was even separating from the rim and creating a void where the tire would get torn. My rim being extremely narrow must have been a factor.

My tire changing method has probably gotten a bit better too (after all that practice), but I'm pretty sure the tape was at fault.

This thread brings back bad memories - that was a dark time. Right after I fixed this problem I had a rash of pinhole flats. Now I have a Gatorskin on the back (since that cheapo tire was getting worn with 1200 miles on it), and I put a thorn resistant tube under that, and I added slime to my front tire. So far so good.
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Old 03-03-11, 07:27 PM
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too much tape can cause the tire to not seat correctly. also a tear in the tube should result in an explosion. sounds like a fire cracker or gun going off. tear would not result in a slow leak. the first tire i changed i managed to get part of the tube under the tire between the wheel. result was a blow out about a mile down the road. ever since i have spent more time making sure the tire and tube are correctly installed all the way around.
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Old 03-04-11, 11:23 AM
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I wasn't present for any of the 3 inside tears. They may have sounded like fire crackers for all I know. My "forensics" clearly indicated a tear, not a puncture.

Do you mean too much tape can cause the tube to not seat correctly? None of my excess tape impinges on the beads - so there's no interaction between my tape and my tire.

I think my tubes were not seating correctly previously, and it has to do with the combination of the particular installation of Velox, and my rim cross section, which is very narrow and pear-shaped, with the fat end of the pear facing the tire. On the walls of the narrow end, the Velox was not form-fitting and it was irregular. Probably I could have also fixed the problem by removing and replacing the Velox, and maybe Velox isn't the best tape on these rims, but in any case I applied enough thin plastic tape to smooth out the imperfections in the Velox, and that clearly works.

Last edited by christofoo; 03-04-11 at 11:50 AM.
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