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Gunshot tube explosion

Old 12-13-06, 06:09 PM
  #1  
rousseau
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Gunshot tube explosion

I've had three gunshot tube explosions in the past two days. The first was while I was waiting at an intersection. Damn near gave the guy in the station wagon across the road from me a heart attack. The second happened overnight--I found the tire clear off the rim, with the tube pretty much blown apart. The third happened after a short ride. I was on my way home from the bike shop with new tubes and a new tire when it went bam! I didn't lose control, thankfully.

My front tire is rated for 100 psi, but I've been running it at 120 psi. I've only put about 500 kms on it. So it blew yesterday. I changed the tube, pumped it up to 110 psi, and this afternoon when I went in to the garage I found the thing in the same condition. I changed the tube yet again, but this time only pumped it up to 105 psi. But it blew again.

I've got different tires on my front and bike. The guys at the shop told me that some tires just fit certain rims better. And it's true, the problem tire on the front certainly does feel looser than the back. They figured that was what was causing the problem. So I went and bought another tire, this time the same brand and make as the one I have no the back.

Does that explanation for this sound right?

Last edited by rousseau; 12-14-06 at 07:18 PM.
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Old 12-13-06, 06:37 PM
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Robert Gardner
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I think you must not be seating the bead of the tire properly and perhaps pinching the tube. The other possibility would only be that your gauge by which you are measuring your tire pressue is way off and you are pumping the tires up to an extreme presure. I always add about ten more psi than recommended by the tire sidewall and never have any problem. I have only had one tube distroyed in a blow out and that was because it was pinched under the bead. Your case is unusual and you are doing something wrong.
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Old 12-13-06, 06:56 PM
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Brand new tubes? Sounds like you need to check your pressure guage.
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Old 12-13-06, 07:31 PM
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Hmmm, I didn't consider the gauge on my pump. It's been cold the last few days, a few degrees above freezing, and I've been leaving my pump outside overnight. I wonder if that would affect things?

As for not seating the tube properly, the second tube was installed by the guys at the bike shop, so I'm thinking that's not a problem.
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Old 12-13-06, 07:38 PM
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Have you checked the inside of the tire for debris or anything that could cause a puncture?
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Old 12-13-06, 07:52 PM
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yeah
what did the tube look like where it broke ??
is your rim tape in good shape ?
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Old 12-13-06, 07:53 PM
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Max pressure rated at 100 psi, but you inflated them over the max and are surprised they blew off like they did?
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Old 12-13-06, 08:04 PM
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Originally Posted by rousseau
Hmmm, I didn't consider the gauge on my pump. It's been cold the last few days, a few degrees above freezing, and I've been leaving my pump outside overnight. I wonder if that would affect things?

As for not seating the tube properly, the second tube was installed by the guys at the bike shop, so I'm thinking that's not a problem.
Actually, seating the tube is not quite what you need to look at, it's seating the tire to the groove in the rim that you need to look at. The tube relies on the rim and tire to hold it's shape and integrety. If that's what you really meant and I'm just nit-picking, my apologies. It's very true that, due to manufacturing tolerances, different tire and rim combos fit significantly different.

I trust my own eyes much more than just about any shop guys. Mainly because it's my bike and I have much more interest in things being done just right as opposed to getting it done quick and on to the next job. Some mechanics are excellent and have high standards like me, but it seems just as many are just there to rush through jobs and move on to the next thing.

In the case of problem tire/rim combos, I have kind of a ritual. First, I use a bit of talc on the tube and/or inside the tire to keep the tube from sticking anywhere and getting pinched or twisted. Before inserting the tube into the tire, I put just enough air in it to give it a bit of shape and to keep it from letting a flat fold get caught between the tire and rim. When the tire is in place, pump it up just enough for the tube to fill the tire, like maybe 10 psi. Then I visually check the tire all the way around on both sides to make sure the whole bead is even and not hanging over the edge in one spot. In some cases, I will roll the tire back and forth as I go around to make sure it's catching the rim groove evenly. Then go ahead and pump it up to full pressure.

I have a few tire gauges that vary quite a bit. One gauge (the one on the pump) will read my commuter tire at 70 psi while the next (My Accu-gauge) will read the same tire at 90psi. The third (Topeak) reads just under the Accu-gauge. I go with the Accu-gauge because it was most expensive and I figure the least chance of overdoing it. If you are going 20% over and the gauge is reading another 20% low, that may be pushing it too far.

How old is the bike and rim? Is it newish 700c stuff or older 27" stuff? If this is an older rim, it may not be designed or have a groove that can take the high pressure.

Anyway just some things to think about.
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Old 12-13-06, 08:49 PM
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Originally Posted by DieselDan
Max pressure rated at 100 psi, but you inflated them over the max and are surprised they blew off like they did?
Nah, that wasn't it. The real blow-off pressure for a properly seated tire is at least twice the maximum sidewall pressure recommendation. Either the tire wasn't seated properly, the tube was caught under the tire bead or the rim has been damaged.
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Old 12-13-06, 09:03 PM
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Originally Posted by HillRider
Nah, that wasn't it. The real blow-off pressure for a properly seated tire is at least twice the maximum sidewall pressure recommendation. Either the tire wasn't seated properly, the tube was caught under the tire bead or the rim has been damaged.
Okay, now this is starting to get me thinking...I wonder if the rim has been damaged somehow? Otherwise, why would I suddenly be getting these gunshot tube explosions out of nowhere? Thing is, I haven't dropped my bike or had an accident or anything.

The tubes have all been completely blown apart. They literally exploded. The last time, when I was in motion, the tire came right off the rim on both sides, the lip basically jumped from inside the rim to the outside of the rim, allowing me to coast to a stop without too much wobbling.
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Old 12-13-06, 10:46 PM
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I was having a similar problem with a slightly larger tyre and slightly smaller rim, both brand new, so no debris etc. Over time the tyre would come unseated then BANG! My solution was to swap some tyres around and voila! No more explosions and alarmed cats in the garage.
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Old 12-14-06, 12:15 AM
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I've put 2,600 kms on these wheels. I bought the bike used, so who knows how many more were put on them previously. Do rims "wear out?"
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Old 12-14-06, 04:32 AM
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I've had all those things happen on my Schwinn World Sport with its original 27" rims - the tires were rated for 90-100 psi or so, but I found those steel rims couldn't hold that.
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Old 12-14-06, 07:03 AM
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Originally Posted by rousseau
I've put 2,600 kms on these wheels. I bought the bike used, so who knows how many more were put on them previously. Do rims "wear out?"
Rims "wear out" most commonly by abrasion thinning out the brake track until they crack or by cracking around the spoke holes from fatigue. It sounds like mechanical damage if your rim is really the problem.
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Old 12-14-06, 07:38 AM
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What about replacing the tire? I had problems in the past with tires that have been removed and reinstalled several times beginning to blow out like this. And I've changed hundreds of tubes in the back of a shop so I can seat a tire properly, check for debris, etc. Replacing the tire solved my problem.
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Old 12-14-06, 07:38 AM
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Some of the older rims didn't have bead grooves and tubeless rims no groove. Just a thought!!!
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Old 12-14-06, 08:02 AM
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I'm kinda with DieselDan on this one. You don't know you have a real problem unless the tire blows off at the designated 100psi max.
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Old 12-14-06, 08:19 AM
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Originally Posted by rousseau
I've had three gunshot tube explosions in the past two days. The first was while I was waiting at an intersection. Damn near gave the guy in the station wagon across the road from me a heart attack.
Was it loud enough that a jet pilot would have heard it from the cargo hold?

Sounds to me like you just got the odd tire that was a little too big.
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Old 12-14-06, 08:38 AM
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Check your pump gauge.
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Old 12-14-06, 09:24 AM
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Wrong tube size???? So it's stretched?

(but yeah, maybe something is cracked in your pump from being left out in the cold?)
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Old 12-14-06, 11:59 AM
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Originally Posted by HillRider
Nah, that wasn't it. The real blow-off pressure for a properly seated tire is at least twice the maximum sidewall pressure recommendation. Either the tire wasn't seated properly, the tube was caught under the tire bead or the rim has been damaged.
That is a pretty general statement that is generally wrong. At least double you say? I dare you to try to get any road clincher to 240psi, or any MTB tire to 160psi. Can my tubulars take 500psi?
We've tried for kicks. "real" blow offs occur at much much lower pressures, not surprisingly for this post , anywhere from 20-50 psi above the mfgs listed max limit.
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Old 12-14-06, 01:24 PM
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Originally Posted by AfterThisNap
That is a pretty general statement that is generally wrong. At least double you say? I dare you to try to get any road clincher to 240psi, or any MTB tire to 160psi. Can my tubulars take 500psi?
We've tried for kicks. "real" blow offs occur at much much lower pressures, not surprisingly for this post , anywhere from 20-50 psi above the mfgs listed max limit.
I don't know where the blow off point is for tires (I don't care to try), but the OP was 5-20psi over max. There is no way lawyers would let the stated max be so close to the failure number. That really should not be sufficient to blow a tire assuming his pressure gauge is reasonably accurate.

My first bet is still on faulty installation followed by rim damage, debris in the tire wall, or rim tape trouble. It would be useful to know what model and year the rims are to tell if they do not have the right hooks on the rim for high pressure tires.
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Old 12-14-06, 02:47 PM
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What width rims and tires do you have? Sounds like the tires are pretty big (if they have a 100psi max). Maybe a combo of narrow rim, large tire size, over inflating, and off-spec tire were combining to give you a hassle. The 'gun shot' blowout probably means that debris in the tire and rim tape trouble are not the problem. Woudn't those things cause a typical leaking flat? The safety factor is supposed to make up for manufacturing tolerances.
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Old 12-14-06, 02:50 PM
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Originally Posted by barba
My first bet is still on faulty installation followed by rim damage, debris in the tire wall, or rim tape trouble. It would be useful to know what model and year the rims are to tell if they do not have the right hooks on the rim for high pressure tires.
I will get that information presently, but I'm kind of an "in-one-ear-out-the-other" kinda guy when it comes to brand names. In any case, I replaced the tire today and had a successful ride with no blowouts, so knock on wood.

The best deduction the bike shop has come up with so far is that there were most likely two factors involved, the first exacerbating the other:

1. The gauge on my pump is off, most likely having to do with the near-freezing temperatures of the garage in which I have left it in for the last four days (as opposed to inside the house, where it was when I had the bike on the trainer during the snowy weather).

2.This particular tire, rated 100 psi, just happened to not work well with my particular rim when pumped up to 120 psi (or 115 psi, or 105 psi--bam! bam! bam!), all of those figures most likely being nominally quite lower than what I was actually pumping into the tubes as per factor no. 1.

Does this sound reasonable?
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Old 12-14-06, 03:13 PM
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Originally Posted by rousseau
I've put 2,600 kms on these wheels. I bought the bike used, so who knows how many more were put on them previously. Do rims "wear out?"
I was riding once when I heard something like a gunshot. Turns out the sidewall of the rim catastrophically blew out. I had a lot of miles on those wheels. So yes- rims eventually wear out.
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