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First flat: is this normal?

Old 09-18-16, 09:47 AM
  #1  
jefnvk
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First flat: is this normal?

So, after an estimated 2200 miles or so after I started riding bikes again in the fall of 2014, I finally got a flat. I did so in epic fashion, with a bang loud enough that a cop working the event came over and said I had him reaching for his gun because he thought there was a shooter (the ride I was on wasn't going through the nicest part of Detroit at that point).

Anyhow, pulling out the old tube, I saw this. The tube seemingly ruptured down a manufacturing seam. Is this one of the oft talked about pinch flats, or is this possibly some sort of manufacturing mistake? The tube in question has about 500 miles on it. Tube was pumped to about 85PSI an hour beforehand.
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Old 09-18-16, 09:55 AM
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Not a pinched flat. That's a blow out. When you hit something and the air escapes at the weakest point, which happened to be the seam. Yikes!
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Old 09-18-16, 09:56 AM
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I does not look like a pinch flat, nor any flat I've ever seen. Possibly a defective tube, yes. Anything abnormal visible on the tyre ?
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Old 09-18-16, 09:57 AM
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I suspect an installation error problem. tube pushed the tire off the rim. a Blow Off.

when you put the new tube in, go around the wheel. make sure no tube remains under the tire bead

That it is entirely between them .. stem is often where people dont check this, did you?




./.
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Old 09-18-16, 10:01 AM
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Pinched between the tire and rim near the valve stem.
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Old 09-18-16, 10:13 AM
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First of all, understand that tubes don't have seams. What looks like a seam isn't one at all, it's a raised line resulting form the seam in the mold. The tube's rubber is perfectly continuous below that line.

This kind of split usually happens when an improperly seated tire blows off the rim. However it can also happen without the tire blowing off if the rim is narrow. Narrow rims limit the space between both sides of the tire at the bead level. There's space in the rim below this narrows and as the tube inflates, it first lays across the narrows, then that narrow unsupported strip blows down to fill the space below.

So a narrow section of the tube is stretched much more than the rest, and can be at it's limit just waiting to blow. This hyperstretch effect is why some people can go for a long time before a flat, then have a number of these splits happen quickly with new tubes.
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Old 09-18-16, 10:53 AM
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Inner Tubes | How It's Made | Discovery Science

Interesting video on how tubes are made. They are extruded with the only seams being where the two ends are joined and the valve is is added.
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Old 09-18-16, 11:05 AM
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Originally Posted by FBinNY View Post
First of all, understand that tubes don't have seams. What looks like a seam isn't one at all, it's a raised line resulting form the seam in the mold. The tube's rubber is perfectly continuous below that line.

This kind of split usually happens when an improperly seated tire blows off the rim. However it can also happen without the tire blowing off if the rim is narrow. Narrow rims limit the space between both sides of the tire at the bead level. There's space in the rim below this narrows and as the tube inflates, it first lays across the narrows, then that narrow unsupported strip blows down to fill the space below.

So a narrow section of the tube is stretched much more than the rest, and can be at it's limit just waiting to blow. This hyperstretch effect is why some people can go for a long time before a flat, then have a number of these splits happen quickly with new tubes.
Oh they have seams. Perhaps not where that blow out happened, but they have seams.
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Old 09-18-16, 11:20 AM
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Originally Posted by texaspandj View Post
Oh they have seams. Perhaps not where that blow out happened, but they have seams.
They have exactly one seam; and that would be where the two ends of the tube are joined together.
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Old 09-18-16, 11:21 AM
  #10  
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Originally Posted by texaspandj View Post
Oh they have seams. Perhaps not where that blow out happened, but they have seams.
It depends on what you call a seam,

Tubes have a lap joint, where both ends are joined to form the circle, then the tube is inflated against a hot mold to set the final shape.

So for all practical purposes they are seamless and what people think is a seam is simply a mold mark. This becomes obvious if you cut a tube open and look at the inside surface.
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Old 09-18-16, 12:03 PM
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It looks to me like this tube failed due to an improper seated tire bead
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Old 09-18-16, 12:05 PM
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2200 miles aint bad between flats.
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Old 09-18-16, 12:05 PM
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I had an entire series of tube failures like this about 3 years ago. Using cheap Chinese tubes from Wally World. Most of mine blew up during the inflation effort. Always right next to the valve. Blamo! Anyhow, I did some research & discovered heavy "thorn proof" tubes from various on-line sources. Now, all I ever use is the heavy duty thorn proof tubes on all my bikes. Haven't had one blow out since.
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Old 09-18-16, 12:14 PM
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The last flat I had was from when a roofing staple decided to introduce itself to my rear tire.Had to replace the tube as the staple cut about 5 holes all around the tube, and my patchwork ended up failing. I've never seen anything like yours, but I agree with the other posters, as it seems like a defective seam.
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Old 09-18-16, 12:37 PM
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I agree with the bad tire installation theory. The tire was not seated properly.
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Old 09-18-16, 12:50 PM
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Originally Posted by Ilbiker View Post
Inner Tubes | How It's Made | Discovery Science

Interesting video on how tubes are made. They are extruded with the only seams being where the two ends are joined and the valve is is added.

Not all tubes are made this way. Cheaper ones are bonded strips.

Continental tubes are extruded in one piece. That is why I use them and why they don't fail as pictured above.

I hope @jefnvk can tell us what brand/model tube he was using. My guess is that it was a bonded tube and the seam failed.


-Tim-
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Old 09-18-16, 01:02 PM
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Or over inflation
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Old 09-18-16, 01:06 PM
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Originally Posted by TimothyH View Post
I hope @jefnvk can tell us what brand/model tube he was using. My guess is that it was a bonded tube and the seam failed.


-Tim-
I sure can. Standard 700x28-32 Forte from Performance, in a 27x1-1/4 Pasela. Nothing notable about the tire, nothing visibally wrong and I ran my finger around on the inside when the tube came out to make sure nothing was in there. Tire did not come off the rim. Replacement tube functioned just fine for the remaining 25 miles.

I'll check out if is just a mold mark when I get home, I just assumed it was a seam because it followed that line perfectly.

What is the proper procedure to ensure the tire does not pinch the tube? I put one side of the tire on, tube in, pump it just enough so it is round and not folded over on itself, put the other side of the tire on, feel it to make sure it is firm and consistent, then pump it up.
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Old 09-18-16, 01:13 PM
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Originally Posted by TimothyH View Post
Not all tubes are made this way. Cheaper ones are bonded strips.

Continental tubes are extruded in one piece. That is why I use them and why they don't fail as pictured above.

I hope @jefnvk can tell us what brand/model tube he was using. My guess is that it was a bonded tube and the seam failed.


-Tim-
I agree. Seam? There is no seam. Hah.
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Old 09-18-16, 01:14 PM
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Punctures
A nail or glass will make a small puncture hole, and the tire will deflate with a hiss, not a bang.

Splits
A long split like that happens when the bead slips off the rim. The tube inflates like a balloon, since it's not held back by the tire, and pops with a very loud bang.

I think a tube failure would be a much smaller length split, more like 1/4 inch or so. I've had that happen. Since the tube is still constrained inside the tire, it's hard for the split to keep growing to many inches, since all the air is dumped out as soon as the split starts growing.

Tubes trapped under the bead
When installing a new tube, once the tire is mounted, I go around both sides and push the tire bead toward the center of the tire, making sure there's no tube showing at the bead edge.

I've had a fold of a tube caught under the bead before. After a couple of hours, it finally pushed the bead off the rim, and did the loud !bang!



Tubes at the valve
It's easy for the thicker part of the tube at the valve to get caught under the tire bead, since it's stiff. The fix is to always push the valve inward toward the tire tread before inflating the tube the first time. This makes sure the tube is all inside the tire there. Pumping up the tire will push the valve back out to it's normal length.

This seems likely in your case, since the split is near the valve.

Checking the molded line on the tire
After inflating, I hold the axle in both hands and spin the tire by pulling on a spoke with a finger.
I sight along the metal rim edge, and watch the molded line in the tire for a consistent distance from the rim. Sometimes, part of the bead is too far down in the rim, and I see a dip there. The tire tread usually shows a wobble, too.

That low bead section can let a different part of the bead pop off the rim easier.



Too much air pressure
How big are your tires? If they are over an inch across, your 85 psi is likely too high. (too high for comfort and efficiency, and perhaps a cause of the tire coming off the rim.)

And older rims didn't have a "bead hook", a small bulge at the edge of the rim, to help hold in the tire. They just had a straight side on the inside of the rim, and riders had to be careful not to overinflate.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

EDIT: I see your reply above:

Originally Posted by jefnvk View Post
I sure can. Standard 700x28-32 Forte from Performance, in a 27x1-1/4 Pasela. Nothing notable about the tire, nothing visibally wrong and I ran my finger around on the inside when the tube came out to make sure nothing was in there. Tire did not come off the rim. Replacement tube functioned just fine for the remaining 25 miles.

I'll check out if is just a mold mark when I get home, I just assumed it was a seam because it followed that line perfectly.

What is the proper procedure to ensure the tire does not pinch the tube? I put one side of the tire on, tube in, pump it just enough so it is round and not folded over on itself, put the other side of the tire on, feel it to make sure it is firm and consistent, then pump it up.
That 1 1/4 tire is essentially a 32mm width. Unless you are well over 200 pounds, I'd try 65 psi front and 80 psi rear. (And try even lower pressures!) It'll ride a lot better. But your 85 psi isn't high enough to blow the tire off the rim.

I think that a part of the tire bead must have come off the rim. Perhaps it popped back on after the explosion, as the wheel rolled, since there was no more force on the bead. That's not unusual, I've seen other forum reports of big splits where the tire seemed to be on the rim.

See my comment above, I look down on each side of the tire bead when changing tires.
And check the tire mold line to make sure the bead is set evenly, too.

Last edited by rm -rf; 09-18-16 at 01:38 PM.
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Old 09-18-16, 01:15 PM
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Also as far as I was aware, I didn't hit anything of note when it blew. Just a loud bang and a fun shaking sensation on straight flat road. May have been some minor bump, but nothing big.

Of course, it also happened in a downpour. Learned the important lesson if you have one Schrader and one presta valve on the bike, and only carry one spare tube, make sure the presta stem saver actually fits in your Schrader hole. Mine didn't. Luckily the fiancee had her Schrader spare. Happy to say even with the fiddling of the stem saver for a few min, I was done in a shade over ten min.

As always thanks for the help!
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Old 09-18-16, 01:20 PM
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It may well be that tubes are essentially seamless except for a lap joint at the ends of an extruded rubber tube. At the same time, some tubes have thin areas that may possibly be the cause of split sides. I say this because when I buy new tubes I pump some air into them and put them aside overnight to check for leaks or weak spots. Frequently, one section of a tube will balloon out well more than the rest of the tube. I see no point in installing a sketchy tube 30 miles from the house. Whether this tinning will cause the splits I can't say but I'd rather err on the side of not walking any real distance pushing a bike.
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Old 09-18-16, 01:24 PM
  #23  
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Originally Posted by FBinNY View Post
......

Tubes have a lap joint, where both ends are joined to form the circle, then the tube is inflated against a hot mold to set the final shape.

...
Well, they DID like 50+ years ago, and some of the lower-end tubes were still made this way about 10 years ago (mostly cheap tubulars from Thailand), but for the most part, essentially ALL tubes sold here since at least the mid '70's have been made from round molds. Lap joins leave a lump underneath the tire, and have gone out of favor. Even Wal-Mart doesn't sell such tubes any more.
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Old 09-18-16, 01:32 PM
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You May mistake where the Mold sections separate to let the otherwise seamless inner Tube come out .
in order to re close to produce the next inner tube.
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Old 09-18-16, 01:52 PM
  #25  
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Improper tire mounting. I'm guessing the tire was recently mounted on the rim, asy within the last week or so. Tube was stuck under bead, and eventually blew out. This would not happen if the tire/tube were mounted properly; it is the tire's job to withstand the internal pressure, the tube only has to seal the inside of the tire.

edit: As I think about it, some tire/rim combinations fit so loosely that this can happen despite the best efforts to the contrary. If the tire is so loose on the rim that you can't get it to seat properly all the way around, get a different brand tire.
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