Inner tube split - help figuring out a flat
 

Hi there -

First time poster here - I recently started riding to work on a commuter bike and all was going well until I got a flat tire that I can't seem to fix. I have 26x1.95 city tires with 26x1.9/2.125 sized inner tube, usually inflating to 55 psi, and my commute's 10 miles round trip on paved roads.

The flat happened on the inside of the inner tube facing the rim and deflate in seconds. I found a slit on the inner tube about 2mm long when I got the flat, and tried patching it with a glueless patch (I know I should use an glue patch, but it was all I had a time and I figured it would at least last me until I got home). However, the patch blew out when I was re-inflating the wheel at about 50 psi and the slit got a bit longer. I tried another patch and same thing - pics below of the blown patch and split that is now about 1" long. The split happens near the seamline of the rim if that matters.
http://bikeforums.net/attachment.php...hmentid=456255 http://bikeforums.net/attachment.php...hmentid=456256

I've checked the rim, rim tape and tire for any debris/splits and can't find anything. The rim looks to be in good shape - e.g.: not bent or anything.

I have a new tube I'm planning to install, but wanted to see if I missed anything so the same thing doesn't happen with the new tube. Any thoughts/explanations as to why this is happening would be much appreciated - I'm a newbie at this.

Thanks!

my best guess is that the lengthening of the original hole was a consequence of the failure of the first patch.

anyway, carefully check the inside of the tire and rim for debris and protrusions, then put in a new tube. a hole that large can be difficult to patch successfully, IME. and stay away from those glueless patches, for heaven's sake! :lol:

I surmise the glueless patch held long enough for the tube to stretch everywhere but at the at the patch.
Glue joint fails and the tube stretches in that spot to fill the contour of the rim, lengthening the slit in the process.

I haven't had a glueless patch fail inside a tire, but I size my tubes close to tire size.
When I've had them fail was when I was patching a tube for a subsequent flat.
When I blew up the tube oversize to find the leak, the patch wasn't strong enough to constrain the tube from stretching and failed then.

Not good enough. The single most important step in repairing a flat is diagnosing and correcting the cause. Failing that just wastes time/effort/money on attempted repairs (as you have experienced).

I suspect that you may have those wide tires on a fairly narrow rim. That can cause tubes to fail on the rim side, as described below.

The tire forms an Omega shaped cross-section, which is pinched in at the bottom by the rim. There's a gap between the tire beads at the bottom, with more room below.

When you first start pumping the tube it assumes a circular profile as in the sketch below.
http://bikeforums.net/attachment.php...hmentid=456322
As you increase pressure, the section spanning the gap blows down to fill the space below the beads (above in the sketch) stretching more than the rest of the tube. On very narrow rims, this additional stretch is more than the material can tolerate and leads to small tears.

Your photo didn't show the whole tube, but you'll often see evidence of that additional stretch along the belly of the dead tube.

Using talc inside the tire helps the rube slip and equalize the stretch a bit. My solution is to use the widest tube that fits the tire. That way it's less stretched in the first phase, and has more stretch left over to blow down past the narrows.

Patching on the belly is problematic for the same reason. That area stretches more than average, and is therefore more likely to teat a poorly adhered patch off.

Thanks. that's some great insight to have in my hip-pocket for the future. That's what I like about this place.

scott s.
.

Check your spoke nipples too, more than one mystery flat at the shop was caused by burrs on the screw head of nipples on machine built wheels. The head would get partially stripped and a sharp burr than pokes though the rim strip causes flats, often recurring because it's not usually something you'd notice if you aren't looking for that.