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Discussion Starter · #1 ·
Today-- for the second time, the tube in the rear tire exploded blowing the tire off the rim while riding on the trainer. When it first happened, i thought I tightened the roller too much so today I made sure not to over tighten it and also inflated to only 100 PSI but it blew up again.
What would cause the tube to blow up like this? I did the local group ride two days ago and it was fine. I plan on putting on a new tire in case it's the tire that's the problem. I hope it's the tire as it's pretty old and is suspiciously easy to mount. I just definitely would not want my tire to explode while on a group ride or something...
 

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Most trainers say turn the screw about 1 & 1/2 turns once it makes contact. There should be a little compression, about as much as if you were on the road. I'd check the inside of the tire and rim to see if there is anything that could be causing that. You can also use a lower pressure for the trainer, as you won't be riding over any rocks or glass on it!
 

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Mounting issue?

notwist said:
Today-- for the second time, the tube in the rear tire exploded blowing the tire off the rim while riding on the trainer. When it first happened, i thought I tightened the roller too much so today I made sure not to over tighten it and also inflated to only 100 PSI but it blew up again.
What would cause the tube to blow up like this? I did the local group ride two days ago and it was fine. I plan on putting on a new tire in case it's the tire that's the problem. I hope it's the tire as it's pretty old and is suspiciously easy to mount. I just definitely would not want my tire to explode while on a group ride or something...
It is extremely rare that this sort of flat is anything other than 1) a tire failure, 2) a damaged rim, or 3) a mounting error where the tube was caught under a section of the bead of the tire. Assuming the tire casing and bead are OK and your rim sidewall is not damaged, then all signs point to a mounting error. The fact that it blew on the trainer might just be coincidence. And yes, people have ridden for several days with this problem as the tube slowly worked its way under a larger portion of the tire until it blew.

Had you recently changed the tire or installed a new tube?

Experiments have been done where the tire bead was repeatedly cut but the tire still held presure because the bead is so forcefully pressed into the hook section of the rim sidewall.
 

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Discussion Starter · #4 ·
I recently changed out the rear tire for an old one I had laying around (only a couple hundred miles on it). Is there a correct way to mount a tire? I usually start mounting it on the side opposite of the valve stem and always check to make sure that there is no tube sticking out of the tire before inflating.
 

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When I mount tires, I start at the valve stem, to make sure that the thickest part of the tube is fully inside the tire, as the tube has an extra layer of rubber around the valve stem. Then I work around to the opposite side.

My success rate is pretty high doing it this way. I've only had a handful of tube explode/pinch doing it this way. I work in a LBS, so I'm changing flats everyday. Seems like its been 4-5 flats everyday the past few weeks.
 

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Discussion Starter · #10 ·
Doctor Who said:
The trainer resistance unit is too tight.
That's what I'm leaning towards. The wheel seems fine and put in a new tube and different tire. I'll report back if it happens again after my ride tomorrow
 

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If you heard a loud pop.

notwist said:
That's what I'm leaning towards. The wheel seems fine and put in a new tube and different tire. I'll report back if it happens again after my ride tomorrow
Keep in mind how a tube explodes: it first has to escape the confines of the tire-rim combination before it can explode with a loud pop. The two events happen at almost the same time, but the escape always comes before the explosion. A tube inside an uncompromised tire-rim unit can't explode.

One remote possibility other than a bad installation, damaged rim or a tire defect is the tire bead "smearing" out of its seat because of high rim temperatures. The tire rubber in the bead area actually melts a bit and allows the tube to push the bead up. But rim temperatures have to be extremely high—too hot to touch for long. I've haven't seen this on a trainer, yet.

/w
 

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I have had it happen once. I was using a patched tube. Patched tubes and trainers don't mix.
 

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Haven't had a tire explode, but using my computrainer all winter, I used to go through tires rather quickly-- until I picked up a trainer specific tire, I think continental is the manufacturer. 2 years later it's still on there, and I do some heavy duty riding on that thing from december thru march.

they're designed so they don't build up as much heat, which could be your problem.
 

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Discussion Starter · #14 ·
I realized that both tubes were ripped in about the same spot -- a couple of inches from the valve. Can this point to something or just a coincidence?
 

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If both tore in the same place, and you mounted the tires the same both times so you have a reference point for the tubes, it sounds like a problem with the rim. It would be very odd for you to mismount the tire twice in exactly the same way to cause a flat from the tube being pinched. Inspect the rim and rime tape in part of the wheel and see if you find anything sharp or rough. Even a small hole in the rim strip can cause problems with tubes.
 

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Major clue

notwist said:
I realized that both tubes were ripped in about the same spot -- a couple of inches from the valve. Can this point to something or just a coincidence?
You said you started the tire at the opposite side from the valve, so that means you're putting the tire on the rim right near the valve. This just about confirms that you are gettting the tube caught under the tire - as someone noted the tube is thicker there and so you have to be sure that you've got it all the way inside the tire.

Four things you should do to prevent this problem:
1) put the tire on at the valve first
2) put a little air in the tube before you install it to help it hold its shape and not get caught under the tire
3) before you start inflating, push the valve up into the tire to make sure it's not caught under the bead
4) before you start inflating, work the tire all the way around with your fingers to make sure the tube is totally inside the tire
 

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Or not

spookyload said:
I have had it happen once. I was using a patched tube. Patched tubes and trainers don't mix.
IME, a properly patched tube is no more likely to flat than a new one. Why would patches and trainers not mix?
 

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wow.....I have thousands of miles on my mag-trainer, and as a matter of fact, I wore one resistance unit out and have never had a blowout in probably 12 or 13 years.
 

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Discussion Starter · #20 ·
Kerry Irons said:
You said you started the tire at the opposite side from the valve, so that means you're putting the tire on the rim right near the valve. This just about confirms that you are gettting the tube caught under the tire - as someone noted the tube is thicker there and so you have to be sure that you've got it all the way inside the tire.

Four things you should do to prevent this problem:
1) put the tire on at the valve first
2) put a little air in the tube before you install it to help it hold its shape and not get caught under the tire
3) before you start inflating, push the valve up into the tire to make sure it's not caught under the bead
4) before you start inflating, work the tire all the way around with your fingers to make sure the tube is totally inside the tire
okay - i always just followed the instructions here: http://velonews.competitor.com/2010...faq-avoiding-that-frightening-blow-out_103005
which recommends starting to mount the tire opposite from the valve stem
 
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