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Why do tubes blowout?

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Why do tubes blowout?

Old 07-05-19, 07:41 PM
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beach_cycle
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Why do tubes blowout?

I just had two tubes blowout while inflating. I've been changing tires about 40 years, but 22 of those years I drove cars and motorcycles, and rode buses 12 years, so technically changed bicycle tubes only 6 of those years. Nevertheless, my success rate is high (99%). I put over 3,800 miles on my Meridian trike last 12 months, and the drive tire is worn most. It damaged a tube prematurely, so I replaced it. I got the tire over the phone, and it doesn't match - not even close. The OEM tires are 26" x 2.0" with a slick tread and the replacement is 26" x 2.25" with a knobby tread. So I was going to put the worn tire on the NDS, and rotate that on the DS. But I blew the original tube while inflating in the worn tire; put in a new tube and successfully inflated it. Next I started to change the drive-side tire, but after mounting it, the non-drive side tube randomly started leaking air and went flat in under 30 seconds. I thought mounting it was a bad idea, so I unmounted the tire from that side, and mounted the replacement back on the DS. When inflating, it blew out. I left them for tomorrow.

When I install new tubes, I have success. I don't have budget for new tires right now, so I tried my luck rotating old tires on rims. Didn't work out. The tires claim to hold 40-65 PSI, and I rode them at 65 PSI +/- for the life of the bike, but today they blew out while inflating at 30 & 40 PSI respectively. To avoid this in the future, I'm wondering why tubes blow out while inflating?


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Old 07-05-19, 08:25 PM
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Must have been the knobby tread.

Really the key to no inflation blow offs is care. Care to fit the tire and tube WRT the rim. Care to stop the initial inflation at 10-20 PSI and check tire seating. Care while further inflating. Care to check tire seating at 2/3 the end PSI. Care to top off PSI. The ability to see possible bead not being seated during inflation. Andy
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Old 07-06-19, 06:29 AM
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The only reason tubes blow out is that they are not properly constrained by the tire/rim combination. The tubes are the air seal, the tire and rim provide the strength which the tube lacks. When a tube blows out after installation it was almost certainly not installed correctly; often a small section of the tube is caught between the rim and the tire bead. Here is a good article section (the whole article is well worth reading IMO) which details installation of tires: https://www.sheldonbrown.com/flats.h...reinstallation
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Old 07-06-19, 08:26 AM
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boom.. !

Only other thing might be a casing failure, it tears, (or ignored un adjusted brake shoe wears a hole in it)

.. and tube pokes out.
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Old 07-06-19, 09:06 AM
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Some tire/rim combinations are a bit difficult and require a bit of care to assure that the tire is seated well before full inflation. I'm a bit more cautious than Andy, checking the seating incrementally after each 10 psi. Tires usually have a witness line above the bead that serves as a good reference for proper seating.

Good luck.
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Old 07-06-19, 09:11 AM
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Why do tubes blowout?


Sometimes, the cause is cheap inner tubes. I have bought several from my LBS that were defective, in that the rubber thickness is inconsistent. In areas of the inner tube where the tube is too thin, the rubber simply ruptures randomly, and you will typically see a rip in the rubber 2-3" long.

I can post pics if I can dig one of the old tubes up, but there's really not a lot to see, just torn rubber and a large un-patchable hole. And no way to protect yourself, since you can't tell by looking at the tube that it's defective on the inside.

I have posted a few times about these tubes, and heard many howls of derision and accusations of "user error". But people who have had this happen will know exactly what I'm talking about, there are a few of us here.
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Old 07-06-19, 03:00 PM
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When you ask questions on the internet, you have to evaluate the responders. Three of our better ones (Andrew Stewart, dsbrantjr and fietsbob) all gave essentially the same answer - you just have to be super careful with the tire/tube installation process. It's easy to get a bit of inner tube caught under the tire bead. If that tiny bit of inner tube inflates, it will push the tire bead off of the rim and you'll get a blow out.
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Old 07-06-19, 04:07 PM
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Thanks for all the great advice.

Originally Posted by Andrew R Stewart
Must have been the knobby tread.

Really the key to no inflation blow offs is care. Care to fit the tire and tube WRT the rim. Care to stop the initial inflation at 10-20 PSI and check tire seating. Care while further inflating. Care to check tire seating at 2/3 the end PSI. Care to top off PSI. The ability to see possible bead not being seated during inflation. Andy
With success comes carelessness, at least for me. Today, I installed the drive side tire/tube, but did it cautiously using your tips, thanks. I am out of tubes, so the non-drive side must wait for a new delivery (ETA: tomorrow).

Originally Posted by dsbrantjr
The only reason tubes blow out is that they are not properly constrained by the tire/rim combination. The tubes are the air seal, the tire and rim provide the strength which the tube lacks. When a tube blows out after installation it was almost certainly not installed correctly; often a small section of the tube is caught between the rim and the tire bead. Here is a good article section (the whole article is well worth reading IMO) which details installation of tires: https://www.sheldonbrown.com/flats.h...reinstallation
Thanks for the link to the article/video. On the three wheeler, I do not need to remove the rear rims to change tires/tubes, but did per suggestion. And with the braking system, I was able to inflate prior to reattaching the rim, which improves visual inspection of the inward side.

Originally Posted by fietsbob
Only other thing might be a casing failure, it tears, (or ignored un adjusted brake shoe wears a hole in it)

.. and tube pokes out.

Thanks for the reply. My original drive wheel resembles ‘casing failure’. Only 3,800 miles; my old car and motorcycle tires would roll 50,000+/- miles on quality tires. Hopefully, replacement bike tires will roll further with less wear.

Originally Posted by Moe Zhoost
Some tire/rim combinations are a bit difficult and require a bit of care to assure that the tire is seated well before full inflation. I'm a bit more cautious than Andy, checking the seating incrementally after each 10 psi. Tires usually have a witness line above the bead that serves as a good reference for proper seating.

Good luck.
Thanks… so far, so good. Only half way done; those blow outs used up my 26” tubes. New triple pack scheduled to arrive tomorrow; then I can use one for the non-drive side.


Originally Posted by Lemond1985

Sometimes, the cause is cheap inner tubes. I have bought several from my LBS that were defective, in that the rubber thickness is inconsistent. In areas of the inner tube where the tube is too thin, the rubber simply ruptures randomly, and you will typically see a rip in the rubber 2-3" long.

I can post pics if I can dig one of the old tubes up, but there's really not a lot to see, just torn rubber and a large un-patchable hole. And no way to protect yourself, since you can't tell by looking at the tube that it's defective on the inside.

I have posted a few times about these tubes, and heard many howls of derision and accusations of "user error". But people who have had this happen will know exactly what I'm talking about, there are a few of us here.

Interesting, the tires that blew had 2 - 3 inch rips in the tubes. Also, most flats from riding are tiny holes from thorns* but I’ve had one resulting in a 2 - 3 inch rip in the tube.

Thanks for the info.
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Old 07-06-19, 04:19 PM
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Originally Posted by Retro Grouch
When you ask questions on the internet, you have to evaluate the responders. Three of our better ones (Andrew Stewart, dsbrantjr and fietsbob) all gave essentially the same answer - you just have to be super careful with the tire/tube installation process. It's easy to get a bit of inner tube caught under the tire bead. If that tiny bit of inner tube inflates, it will push the tire bead off of the rim and you'll get a blow out.
So true. I liked the replies, and do my best to evaluate them. Those answers you mentioned made me realize I got careless and needed to slow down and get back to basics.
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Old 07-06-19, 04:25 PM
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Originally Posted by Lemond1985
Sometimes, the cause is cheap inner tubes.
Incorrect. The only causes of a tube blowout are tire bead separating from the rim hook, or total failure of the tire.

A tube simply cannot "blow out" while contained inside a tire.
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Old 07-06-19, 04:33 PM
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I think Lemond's post has some merit. While thin rubber is not so likely to cause a blowout it just might. When I buy a new tube, it is pumped up and left out overnight to see if it will hold air. After it is pumped up with about 5 pounds of pressure, it can be seen than some parts of the tube bulge out quite a bit from other parts. Obviously the rubber there is thinner. I don;t see any point in installing a tube that has not passed this simple test.
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Old 07-06-19, 04:48 PM
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Part of this discussion, but not yet mentioned, is "what's a blow out". I have my definition, what's yours? In 45+ years of talking about this stuff with pro wrenches and customers I hear many reporting a "blow out" yet we find far less evidence of a sudden and total loss of tire pressure. Even the noise is inconsistently described during the flat repair sometimes.

So what's your definition? Andy.
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