not_jason

First off, I'd like to apologize in advance if this is one of those subjects that gets beaten into the ground on every page. I tried the search function, but I wasn't exactly sure what to be looking for, so I didn't turn much up. Anyway...

Yesterday I went for a ride on one of my bikes that I've mostly neglected this spring. Last time I filled the tires was a couple months ago, so the pressure was pretty low in both of them. I filled them up to what they said on the sidewall, which I think was something like 80 psi. By the way, it might be a good time to let you know I'm riding an old Raleigh Sprite, so this is your standard 27" wheel. Anyway, I took it for a ride, and about a half mile from my house I started hearing this "chirping" sound in a steady rhythm. Initially I dismissed it, but a few moments later I started feeling a bump, and noticed my front tire bulging in an isolated area. I've been around enough times to know what follows that, so I pulled over and plugged my ears. The tube popped within a few more seconds.

So now I'm a little bit concerned, because while I have had this sort of thing happen to me before, it has always happened with old, clearly defective tires that I never should have been using in the first place. However, I replaced both tires and both tubes not too long ago, and barely ridden on them. I suppose it's a possibility that the tube was just a lemon, but what if that's not the case? What else could cause a tube to blow like this? Before I bother to replace it, I'd like to fully consider any such problems, so this doesn't happen to me again, like when I'm going 30 miles per hour down a hill in traffic or something.

Things that might be relevant: Immediately after the pop, I noticed the bead had come off the rim on one side. This could have been due the pre-burst bulge. I do not believe it was like that when I left the house. I think I would have noticed it. The wheel has probably less than a quarter inch of left to right motion when you spin it. I've regular ridden bikes with far more crooked wheels, but upon looking around on here, maybe I shouldn't? Even unrelated to this particular topic, should my wheels be trued? How much wobble is too much wobble?

DieselDan

Your tire came unseated from the bead when you inflated the tube. You described this almost perfectly, save for the "defective" tire bit.

not_jason

While that would explain the blow out, I'm still not feeling 100% sure. If memory serves, when I pulled over to investigate, the bead was off on the left side of the rim, and that's the side that I was standing on when I filled it up. Had it came out of the bead at that point, would have there been any strong visual indication, or could it have been too subtle for me notice right off the bat? And while I am accustomed to considering the warble in my wheel as too slight to worry about, is there a strong possibility that this contributed? Would such a problem be indicative of any issues with the tire itself?

I'm not trying to be contrary with any of this. I thank you for your help and opinions, I just want to fully explore the issue so I know how to prevent this from happening in the future.

Joe Dog

I blew a tire clean off the rim while it was mounted on a car rack. All you have to do is catch little bit of the tube between the tire and rim. Sometimes it will blow while you are inflating the tire, other times it takes awhile to blow. It does not have anything to do with what side you were on when you aired up the tire - the tire comes off where you pinch the tube or bead comes out. After you mount a tire, just methodically work your way around the tire looking for a good seating of the bead before you fill it up. After a few pumps, do it again to make sure everything is 5x5, then pump up to pressure.

You might also double check to make sure that your rims are compatible with your tires. My wife's Cannondale has old 27 inch rims that do not support modern hook bead tires, so we run lower pressure tires on that one.

not_jason

When I went tire shopping, I was largely concerned with the aesthetics of the tire, and bought gumwalls that looked very similar to the original "Raleigh Sprite" tires that were on the bike when i got it (save for the fact that those were whitewalls, apparently impossible to find in this day and age). I'm pretty sure they are compatible, but it would probably be wise of me to double check. In terms of the tire and the rim itself, what should i be looking for to determine whether or not they are compatible?

Also, for what it's worth, when I got the bike out of the basement, it had about 30-35 pounds of air in each tire. They hadn't gone completely flat. I think I probably changed the tires and tubes about 9 months ago, give or take, and I've never allowed them to go much flatter than the above mentioned 30ish psi. The reason I mention all of this: If the tube gets pinched, does that have to happen upon installation, or can it just happen when the tires get too slack? I like this theory about the tube getting pinched, but I'm still trying to iron out any uncertainty and confusion here.

Wordbiker

Inspect the tube that blew.

There should be an impression on it left by the seam between the tire and rim. If the blowout is there, it was either a pinched tube or a tire edge that was sharp enough to cut the tube once you rode it. Check for twists, sharp edges on rim tape/strips, exposed spoke nipples or rim holes, burrs on the rim and embedded objects.

You're on the right track: as important as replacing the tube, always find out why it flatted in the first place and fix the issue.

Closed Office

One thing you have to be careful of when inflating tires is to make sure that the wire bead is set evenly in the rim. Most tires have a witness line just above the edge of the rim that helps. Time after time when installing a tube there will be a place where the tube wants to come out under the bead. I pump the tire up about half way and check around both sides, all the way. If I do see something start to bulge I start deflating the tube faster than the Lone Ranger could even get a shot off.

The most common place is at the stem unless I've pushed the valve up into the tire before starting pumping to make sure the tire isn't sitting on top of the tube. Generally the tires that take the highest pressure are least likely to have this problem of the tube coming out under the bead. I use 27 X 1 1/4 tires too, and usually buy tires that can take 90 psi, although I only put in a little over 60.

I did have it happen while I was riding recently. There was a little bump from a high spot on the tire. I looked at it to see what the problem was and noticed the edge of the tire was high at one point. I let a little air out and this was enough to let me get home without it popping.

Edit: I should add that I have had this happen at random times. One tire I had been riding on for a month without a problem and then one day at work while it was just parked, the tube slipped out under the bead and went blam.

DMF 

While I don't think this was your problem, also check for sidewall damage. It's sometimes hard to spot. The last time I had to hold the tube up next to the tire and use the puncture to find the damage (yet another reason to always align the label to the valve). A cut or tear in the sidewall will let the tube balloon out and eventually hit something or just pop. To repair, I've had success lining the tire with a section cut from an old heavy-duty tube.

DannoXYZ 

also check your brake-pads and make sure they're not too high and rubbing on the tyre. Look at the hole in the tube, if it's big with star-shaped ragged edges, it's most likely due to the tube being pinched between the tyre and rim. That's really the only way a tube can POP. Unless there's some tyre damage that lets the tube escape, and that's pretty easy to spot.

BTW, bad tubes never pop, the tyre contains all the tube and prevents it from expanding. Bad tubes will only leak and not hold air, they never explode. That only happens when the stiff surrounding tyre somehow no longer encompasses the tube... such as when a pinched spot on the tube pushes the tyre off the rim.