Tube exploded while filling!
 

So, I put a brand new tube into my tire. Filled it up to about 20 psi. Checked the rim all around. Bead was securely in the rim on both sides. White stripe around tire was even to the rim all around. So then I continued to fill it with my electric pump.

My tires (Schwalbe Marathon Plus) have a max of 60 psi, which I always fill it to without problems. However, I was a little past 55 psi when I heard a loud "bang" and all the air gushed out.

Looking at the tube, it was torn open by about a foot on each side of the valve.

Any idea what could have caused it?

I will say that I was going to add sealant to it, but I couldn't get the valve core out. Even used a metal tool, rather than a plastic one. But the tool wouldn't go all the way down into the stem, like something was stuck in there. However, the tube was able to receive air, so I decided to fill it up and ride with it until I could get a new tube.

Puzzling.

I would wait on sealant filled tubes till you get tire mounting down pat. A foot long tube slash is nearly always from a portion of the tire bead not staying overlapped with the rim, the resulting hernia sees the tube balloon out through the gap and finally tear/explode.
There are a few common reasons why the tire bead might not be secure within the rim. The tube can get caught between the rim and tire bead, the valve base can prevent the bead from fully overlapping with the rim, the rim and/or tire might be made "off spec" and are not of matching diameters. All three reasons can be prevented from ending up as you did if the tire bead fit to the rim was done a few times during the inflation, catching the bulging off rim tire bead before the tube blew through the gap.
Besides checking the tire's seating a few times during the inflation one can try to see if the tube is caught under the tire bead before inflation by after mounting the tire/tube going around the wheel and prying the tire back away from one rim side and looking in the rim/tire to see if the tube is visible. The valve base needs to be pushed back up in the rim to allow the tire beads to slide down and fully overlap the rim's sides. Inflate a touch and check the fit as you did. Add 10 psi and recheck. Add 20 more and recheck. I would test inflate the tires about 10%-20% more than they will be used at (WRT the max allowed) to insure the tire is seated well and not creeping up off the rim. Andy

I should have also mentioned another common reason why on inflation a tire can slip off the rim and the tube go boom. If the tire's pressure is low enough and the tire can "float about" the rim if the tires on the ground the weight will push the tire's top up out of the rim. If inflation is noy done slow and tire seating is checked a few times this lead to blow off. Andy

After the pop, was the tube still fully contained within the tire, or was part of the tube outside of the tire?

Well, the force of the pop had pushed the tire off the rim. But, yes, what was left of the tube was still inside.

It is possible you got a bad tube.
Our shop recently, past spring, had a batch of faulty tubes. We bought perhaps 50 tubes and while repairing flats they would burst at the valve. We thought it was us but after it repeated for 10 or so tubes in the same place it was clear it was the tubes. Likely just a problem at the factory. We received credit and that was that. We checked the other tubes and some were faulty the rest were fine. These were 700c tubes with a presta valve.
It can happen.
Make sure when changing a tube to check the rim strip to assure it is still doing its job. Check the tire carefully for the possibility of a sharp shard embedded that will cause a puncture somewhere down the road. Check the tire condition for wear, cuts, etc. Make sure the tube is not pinched under the bead when installing the tire.

No, this flies in the face of reality. The tire didn't get pushed off the rim by the tube blowing out. The tire first was not seated fully and as it crept up off the rim the tube then expanded out that gap and very soon burst. Please understand what is the correct timing of events to better understand how to avoid then again. Andy

My first thought was that when you put the tire on that you had part of the tire bead pinching the tube and it simply failed because of that. However you say that your tire came off the rim so that makes me wonder if the replacement tire is just the wrong BSD. Especially since you allude to having witnessed the tire being evenly mounted all the way around based on the white striping.

Still I suppose if it was the former issue and just the tube pinched between tire bead and rim that it might come unmounted during the failure. However the only times I've ever had a tire come unmounted is when way way overinflated to around 150 PSI or when I didn't actually have the witness line properly witnessed and that also involved being near the max recommended pressure of the tire.

Despite what ever the cause, it's basically poor practices. So pay closer attention next time.

The blowout was almost certainly not caused by a defective tube. Even a defective tube would have simply lost pressure, rapidly or otherwise, without dislodging the tire.

If your rims are hookless, they're more prone to allowing blowoffs than any rim with hooked sides.

A modern tubeless and hookless rim is pictured at right below, but many older bikes, especially those with 27" wheels, had hookless (a.k.a. straight-sided) rims.

https://cdn-0.gravelcyclist.com/wp-c...ined2019-3.jpg

Another way to think of this is that a length of the tube was caught under the lower bead of the tire. As the tube inflated, it pushed the bead up and dislodged it from the rim with the resulting blowout. Operator error is the most likely cause. Always inflate the tube just a little bit before installing to prevent this from happening.

Thanks. That's good to know!

This tube was also a couple of years old, and had been sitting in my closet the whole time. I wonder if that had anything to do with it? Shouldn't have, but who knows.

Thanks again.

I understand what you're saying here. Still, the tear was along the seam, on both sides of the valve, at the very outside of the tube.
If the tire had come off the rim, causing the tube to expand and pop at that point, wouldn't the tear have been on the side of the tube, in the part that came out?
Also, I was watching the tire the whole time, and did not see anything coming out of the tire. Granted, I only saw one side of the tire. But, still, it appeared to be well-seated.

The wheel was off the bike, in the back of my minivan, where I had my electric pump plugged in. The valve was at the bottom of the wheel, and that's where the tear happened, at the valve. So it wasn't at the top.

As noted, I didn't see any hernia. Bead seemed perfectly seated, and nothing was coming out. Then, bam! But, again, I only saw one side of the tire.

So, if the max psi is 60, you're saying to inflate to 70, check the tire on the rim, and then deflate back to 60?

Kai Winters noted above that he experienced bursting at the valve due to faulty tubes. Just FYI.

Thanks for the info about hookless rims.

Very possible it was operator error and not a faulty tube. Still, as noted, I did check the bead and was watching the tire the entire time (though only one side) and didn't see anything.
Even though I checked the bead initially (at about 10-20 psi) I'll start rechecking again after a bit more air is in place.
Thanks.

I do have one 26" tire that I think has stretched or something, and is very difficult to get properly seated. It does happen.

However, I think the VALVE may be key here. The tire was probably partly sitting on top of the valve.

There are two theories of mounting the tube.
I prefer to start at the valve. Get the tire partly on, push on the valve some to make sure it is above the tire, and then work around.

Others believe it is safer to do the valve last, less chance of pinching that last few inches of tube. Nonetheless, once you reach the valve, the procedure is similar. Push the valve down to make sure it gets past the tire. Then pull it up.

If the valve is crooked, also make sure it is straight (often by twisting the tire around slightly).

Then inflate.

The tubes in my bike tires are over a couple years old. The one spare tube in the bike bag too. I guess using that logic, I'm SOL.

However I know from experience that you can use tubes way older than 2 years. The badly stored tube is probably a rare exception.

One of the common tube failures I use to have before I finally learned the last few lessons my tires wanted to teach me was that I simply let the tube get pinched as I was trying to get the bead of the tire over the rim. Maybe you did that too.

There are several variation on how that might happen, but all result in a flat and all with a tear like you seem to describe. All were from my carelessness and being inattentive to things.

Tubes can dry out over time and the possibility of bursting especially at a seam, joint, etc. is increased.

This. The tube didn't pop, sending the tire off the rim. The tire slid off the rim, allowing the tire to balloon out and pop. I only have about 8 years of experience working in a bike shop, many years ago, but Andy has owned shops and built bikes... When Andy answers one of my questions I pay attention to what the man says.

Suggest that you read all of the tips about ensuring that a tire is seated, and remains seated, during the entire inflation process. I'm not casting any aspersions on your abilities or observational powers - we've all blown up a tube when the tire sneaks off the rim. It's just that, if you focus only on a "tube problem", and ignore the tire seating problem, you probably will go through a lot of "bad" tubes....

I'm not doubting that this is what may have happened. I'm only questioning why, if the tire slid off the rim, allowing the tire to balloon out and pop, that I didn't see it do it, since I was watching the tire the entire time. (The tire was off the bike in the back of my minivan while being inflated, and I was sitting next to it, holding it.)
Granted, I was only looking at one side of the tire. But that was the side of the tire which came off the rim. So if the tire came off the rim first, allowing the tube to balloon out, it seems I would have seen it, since I was looking at the tire the whole time, no?
Also (and, again, not arguing, just trying to understand): if the tube ballooned out and then popped, then wouldn't that have been where the tear was, where the ballooning happened? But the tear was along the seam, at the very outside of the tube, not on the side of the tube.
Thanks!

That is weird that you didn't see it. I look at any element of the tire that has a constant diameter and depressure if I see even a slight lack of concentricity. That said, If the thing starts sliding it happens fast. I have to say that when I rebuilt the "hookless" Weinmann rims on my Schwinn Superior I think it took me 1/2 hour of very nervous fill and check, fill and check.

Glad you weren't hurt. Good luck

It was a popped inner tube, not an exploding hand grenade.