TromboneAl

Is the rim tape not smooth enough over the inside of the nipples??

DiabloScott

Did it explode with a bang? or did it just go flat with a poof?
How long had it been in the wheel before it ripped?
Doesn't look like a spoke poke to me, but maybe if it was right at installation and you snagged it.

dddd

Almost certainly, that tube failed because the valve did't come far enough thru the hole in the rim.

Since the tube's thicker rubber pad surrounding the valve stem didn't drop down, the thinner part bulged apart into the cavity below the raised rubber pad.

This happens much mor often with bigger tires on narrower rims.
This because of the sharp angle that the tube and it's rubber pad have to go around (sliding along the bead area of the inside of the tire) the bend from the outwardly-splayed tire sidewall to the inner shape of the rim's sidewalls.
The added friction sliding along that inside corner further prevent's the rubber pad from meeting the inside floor of the rim unless you give the stem a tug during the initial inflation process.

This is very common, btw. Wider rims prevent the problem by allowing the inside profile of the tire's sidewall to be more of a straight line down to the bead itself, allowing the pad to move easily under pressure without getting pinned against the sidewall.

vredstein

Is the split in the same area where the rim tape overlaps itself? If it's hard plastic rim tape, it may have had a sharp edge that caused it.

davidad

Usually that look comes from the tube being caught under the bead and blowing out of the tire with a bang.

FBinNY 

+1 with narrow rims the there's only a small gap between both walls of the tire where they're brought together by the rim. As you inflate it the tube fulls the tire, than the thin section across the gap balloons down to fill the rim. That means the area near the belly is stretched 3-4 times more than the rest of the tube. It's compounded at the valve, because as dddd said the reinforcement near the valve didn't stretch as much so the nearest thin section made a small bubble inflating under it and that was just too much.

The best prevention is avoiding ultra narrow rims, but I don't expect you to chuck your wheels. The other ways to improve things include the following, of which you can do one or more.

1- buy high quality tubes.
2- look for tubes that have a narrow or no flange at the base of the valve, so that it can be pulled down closer to the rim.
3- buy tubes sized closer to the tire so they stretch less on inflation, the best size is the largest that's smaller than the tire. Don't go larger than the tire because that creates new different problems.
4- use lots of talc between the tube and the tire. This will allow the tube to slide around a bit within the tire and equalize the stretch as you inflate.

One thing I do with large tires on narrow rims is inflate to about 5-10 pounds or so, and kind of massage the tire as I check the seating. The theory is that it allows the tube to slide inside and equalize the stretch. Who know if it helps, or is just a bit of superstitious voodoo, but I seem to be able to avoid the problem even on my 2-1/4" tire on a narrow rim.

dddd

"3- buy tubes sized closer to the tire so they stretch less on inflation, the best size is the largest that's smaller than the tire. Don't go larger than the tire because that creates new different problems."

+10

TromboneAl

Thanks for the good info. It was a Specialized 700x20/28C tube in a 700x23C Gatorskin on a wide-rimmed cheap wheel. The tape didn't overlap at the point of the blow.

I had a garage flat (fourth in a row!), and quickly pumped it up to see if I could find the leak and patch it without removing the wheel from the bike. As I was rotating the the wheel with my ear near the tire, it popped.

FBinNY 

Lesson #1 Don't put potentially noisy things near your ears.

Though the type of failure in the photo looks like a classic belly blowout caused by narrow rims, your latest post points in another direction. When mounting tires there are a number of very important steps, whose omission can cause immediate blowouts.



1- Start with a partly inflated tube, just enough to give it shape, so it'll install without twists, or get caught between the tire and rim. (you may have to let some air back out as you finish mounting the tire.

2- The tube is thickest near the valve and it's easy to trap this section, so as a final step push the valve down into the tire to pull the tube with it, then pull the valve back out to it's full length to seat it properly. With narrow rims, you might have to jiggle it a bit to help it pass the narrows.

3- inflate to only 10psi or so (enough to fully shape the tire) and spin the wheel, using the molded lines (not color sections) to see if there are any high or low spots. Tires are very accurately sized to match the rims, so any low spots mean that there'll be slack elsewhere which can cause a blowout. If there are any high or low spots, deflate and massage the tire around the rim until it's seated evenly all the way around. Repeat this step as often as needed until it's right, then inflate to 1/2 pressure and check again before going to full pressure.

Once a tire is properly mounted it tends to stay home so there's no extra work needed when pumping from low to full pressure.

SJX426 

I had a specialied tube blow on me within two rides and it blew in the garage! I looked like it blew on the parting line. Yours didn't.

Al1943

You say you've had 4 garage flats in a row. Did the other flats happen at the same part of the tube?
From your last post it sounds like the rim is too wide for the tire, but I don't know if that is what caused this particular blow-out.

TromboneAl

No, and they were different bikes as well. One was a sidewall blowout that was so big that I couldn't get any air into the tube. It must have happened in the driveway coming home.