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80psi road bike tire BLEW out just Sitting. Normal??

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80psi road bike tire BLEW out just Sitting. Normal??

Old 09-30-21, 07:36 AM
  #1  
777funk
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80psi road bike tire BLEW out just Sitting. Normal??

I'm fairly new to road bikes and as I was working on another bike, and was startled by a LOUD bang (louder than a 22lr, quieter than a 12GA). It was my Puch Cavette sitting about 30 feet away. I went and looked at it and the side wall had jumped past the rim. I pulled the tube and it has a 6 inch split about even with where the side wall of the tire would have been. The tire looked to be in good shape but some of the sidewall's top edge was a little frayed. I don't know if it happened when the blowout occurred or if it was this way before the blow out. It's not sharp to where I'd think it'd damage a tube.

Is this common with high pressure road bike tubes?

Edit to add tire size: 27x1 1/4"

Last edited by 777funk; 10-01-21 at 07:14 AM.
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Old 09-30-21, 07:42 AM
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Just a guess: your old Puch has straight wall rims. Yeah, blowing a high pressure tire off a straight wall rim isn't unheard of, and when it happens everybody will hear it. If you wanna run high pressure tires you'll be better off with hooked edge rims:

https://www.sheldonbrown.com/gloss_ho-z.html#hook

The other possibility is the tire wasn't seated correctly.

You'll do yourself favors to match the tire width to the rim width. Here's a chart:

https://www.sheldonbrown.com/tire-sizing.html#width

Last edited by tcs; 09-30-21 at 07:47 AM.
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Old 09-30-21, 07:54 AM
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80 psi isn't exactly high pressure for road bikes, though it seems to be a common pressure for many on road bikes, depending on tire width. Some road bike tires do have a low max pressure.

Newish tire and folding tire? Check what tcs was asking. If this is a smooth bead rim with no hooks, then most foldable tires won't work well on it. Though I think I did run one on mine, but I do a lot of not so bright things and get away with them.

I have had tires blow off a smooth bead rim. It's quite impressive noise and no evidence of damage other than a blown tube and partially dismounted tire.

You know what witness lines on a tire are and how to use them?
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Old 09-30-21, 08:00 AM
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Originally Posted by Iride01 View Post
80 psi isn't exactly high pressure for road bikes, though it seems to be a common pressure for many on road bikes, depending on tire width. Some road bike tires do have a low max pressure.
80 psi is very high pressure if the bike in question has 27 x 1 1/4" tires and rims without hook beads. 60 - 70 psi for a setup like that would be closer to the realistic maximum
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Old 09-30-21, 08:07 AM
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I blew a tire on hooked rims last week. User error, in my case: almost certainly trapped a bit of the tube under the tire. Over the course of half an hour, the tube ever so slowly pushed the bead up the rim, until the tire bead went over the rim and -- BLAM!

So don't do that. Make sure you've got the tube completely inside the tire, and the tire is evenly mounted all the way around the rim on both sides.
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Old 09-30-21, 08:10 AM
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OP. You most likely Pinched the tube when installing the tire.
I did that one morning when installing new tubes and tires onto New Wheels.
Both of them Blew.
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Old 09-30-21, 08:26 AM
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Originally Posted by alcjphil View Post
80 psi is very high pressure if the bike in question has 27 x 1 1/4" tires and rims without hook beads. 60 - 70 psi for a setup like that would be closer to the realistic maximum
Still it's not too high a pressure. Or at least it shouldn't be material to the OP's tire blowing off the rim. Or I suppose not the important take-a-way piece of info. The important part might be that the tire just wasn't properly seated.

Though till the OP replies, we won't know. I'm just speculating.

I had to get my 27 x 1" up to around 150 PSI to intentionally blow them off my chrome plated steel smooth be rim when properly seated. The accidental times they blew off was IMO, because I didn't have the bead properly seated yet. But those were still better than 100 PSI when they blew off.
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Old 09-30-21, 08:42 AM
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Agree with 10wheels. When you installed the tube, you pinched the tube between the tire bead and the rim. What you described is exactly what happens when you do this. You pump up the tire and, either while pumping or a few minutes later, there is a loud "bang", and when you look you have a rip in your tube.

Nearly all of us have done this at least once.
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Old 09-30-21, 04:37 PM
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Originally Posted by alcjphil View Post
80 psi is very high pressure if the bike in question has 27 x 1 1/4" tires and rims without hook beads. 60 - 70 psi for a setup like that would be closer to the realistic maximum
45 years ago, I was running wire bead 27x1-1/8 tires at 100psi on unhooked rims (Ukai rims that were original to my '75 Fuji) with no problems at all. My second set of rims were hooked and had no issues, but were then replaced with another unhooked set after taco-ing that set while on tour in ~1980... 15 years later, I noticed a trend of replacement 27x1-1/8 tires blowing off even at lower pressures - unless I was very careful to make sure they were seated absolutely concentric on the rims.

I have since upgraded to hooked rims and fixed that....
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Old 09-30-21, 05:38 PM
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A buddy did this to a brand new bike.
His brand new floor pump had an inaccurate gauge.

Store replaced both tires and the pump without hassle.

Barry
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Old 10-01-21, 07:07 AM
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Another vote here for the pinched tube theory. Getting a bit of the tube caught under the bead is actually pretty common, and the resulting blowout can happen any time from a few minutes to weeks after. In fact, I remember one guy in my club whose new bike was getting blowouts on every ride. The shop would replace the tube under warranty only to blow the next ride. Finally a couple of us grabbed his bike before the ride and reseated both tires. No more blowouts. Moral: even shops can screw up and pinch the tube.
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Old 10-01-21, 07:12 AM
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I didn't install the tire (came with the bike). I just inflated it to said pressure and rode it. I parked it and this happened about 10 minutes later. I don't see any hook in the rim (old 70s bike). The condition of the rim looked good (some rust but nothing sharp). I don't know if the tube was trapped but it rode fine at high pressure.
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Old 10-01-21, 01:36 PM
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Most of us have been there at least once. In my case, a friend and I were setting up some bikes in his basement, and we had put some new tires on a 70's Schwinn for my wife. And then out of the corner of my eye, I caught a sidewall bulging. It was like slow motion, but I couldn't move fast enough to let the air out of the tire before it blew!

Good lesson to always check for a pinched tube before pumping your tires up to full pressure. First, make sure your tube has a little air in it before putting it in the rim. Then, after mounting the second bead, start at the valve, and press the sidewall of the tire away from the rim and look inside to see if you see the tube caught underneath the tire bead. Keep moving all the way around the rim, then check the other side. Then, check whether the tire is mounted evenly on both sides. If it's too low in one spot, press it up with your thumbs. If it's too high, press in and push down with your thumbs. Once the tire looks evenly mounted on both sides, you can keep pumping the rest of the way. Done right, you'll avoid any more blowouts.
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Old 10-01-21, 02:37 PM
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Hookless rim - are those tires wire bead or folding? In the days of hookless rims, folding tires did not exist. They worked just fine with wire beaded tires. If your tires are folding, make sure the beads are seated exactly equally. (Spin the wheel with mounted tires and 20-40 psi and watch the little molded line on the sidewall just above the rim. Don't quit until you have no hops or dips in that line on both side.)
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Old 10-01-21, 05:02 PM
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Originally Posted by 79pmooney View Post
Hookless rim - are those tires wire bead or folding? In the days of hookless rims, folding tires did not exist. They worked just fine with wire beaded tires. If your tires are folding, make sure the beads are seated exactly equally. (Spin the wheel with mounted tires and 20-40 psi and watch the little molded line on the sidewall just above the rim. Don't quit until you have no hops or dips in that line on both side.)
Yep, that's the 'secret' when using non-hooked rims.
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Old 10-03-21, 09:33 AM
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I had a bicycle shop install fenders, 30 mm Schwalbe CX Pro Cyclo-Cross tires and a new chain and cassette on a bike. On the way home the bike felt rather squirrley but I thought it was due to the tires. I'd never used knobby cyclo-cross tires before. The next day I checked the air pressure in the tires and it was quite low. I pumped then up to 60 psi and went to the bathroom. Whilst there I heard a loud bang and immediately knew that a tire had blown. When I looked it was the front tire that had blown and it was mostly off the rim. Inspection showed that when they'd installed the tires the bead of the front tire was sitting on the tube.

I'm just glad it didn't happen as I was going over a very busy overpass. Btw, the shop refused to replace the tube when I showed it to them.

Perhaps your tire too was sitting on a portion of the tube?

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Old 10-03-21, 10:49 AM
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Installation error is what caused the blow out. The bead on the tire was not seated all the way inside the rim and the tube pushed it's way out and blew out.
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Old 10-04-21, 08:33 AM
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I agree with wolfchild.

The most common cause of the blow off that you described is pinching the innertube under the tire bead while installing the tire. When you do that it may hold air for a while but eventually the air pressure in the inner tube will find a way to push the tire bead past the rim.

That can happen with hook beaded rims too, just not as often. Back in the days when I rode with only a CO2 cart in my puncture repair kit I learned to be very careful to make sure the inner tube was enclosed in the tire all the way around on both sides before reinflating.
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Old 10-04-21, 08:55 AM
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The pinched tube usually happens in one of two places: either where the valve stem is, or at the place you last got the bead on the rim. Before doing ThermionicScott's process, first push the valve stem all the way in until it either bottoms out on the far side of the tire or you push it flush with the rim. Then let internal air pressure push it back out. That'll make sure the bead isn't sitting on the reinforced part of the tube.
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