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Old 12-02-2012, 01:10 PM   #49
Tim McKittrick
Beastly Adventurer
Joined: Dec 2003
Location: Wasilla Alaska
Oddometer: 1,774
Originally Posted by VACommuter View Post
Well I finally got the wheel off and dismounted the tire. I was hoping for absolution and that I would discover massive damage from road debris. However, that is not the case. Tire is slightly mishapen from flatenning at speed but there is not a mark on it. Beads look good and interior seems fine. The obvious culprit is the valve stem that was completely yet neatly torn off the tube. Rest of the tube looks great and I could not discern any additional holes or punctures. My 2 ounces of dynabeads are still happily rolling around inside the stemless tube. Soooooo, my lesson here as the man earlier states is to use new tubes everytime I mount new tires. I made special pains to make sure the external valve stem nut was not tight against the rim as I heard that can sometimes lead to shearing if the tire slips on the rim. I think I'll try to remount the tire with a new tube and see what that looks like. The tire might be deformed or out of round. Toe color is more normal with less swelling, pain and throbbing. Still bleeding at the nail but seems to be getting better. Course of antibiotics complete and a big bottle of percocet left over for a "rainy day". Any other words of wisdom, possible hypotheses or general abuse?

I had a similar failure with a tubed race slick on my XR650R Supermoto when I was using it at the track- the rear tire suddenly went flat at speed and I drifted wildly through s few corners before successfully stopping the bike. Once back at the pits I found the stem had torn free of the tube and the tire had spun on the rim.

I was also using Dynabeads, and I discovered a single bead to be lodged up under the Schrader valve when I fished all of the bits out of the tire. I suspect the bead got under the valve stem and caused the tire to gradually bleed pressure, and once sufficient pressure was lost the torque on the wheel was enough to spin the tire and tear the valve stem off of the tube, leading to an instant flat.

I thought at the time that I may have caused the failure by adjusting the tire pressure with the valve stem at the bottom 6 o'clock position, and that in so doing may have blown a bead into the core of the schrader valve. However, I would think that this would have caused a persistent and audible leak, and I would hope that that's the sort of thong I would notice. So now I'm not certain as to the mechanism by which the bead got up under the valve core- but I do believe that this is what lead to the tire going flat.

There had been endless discussion about the pros and cons of Dynabeads- and I'm not trying to add fuel to that fire. This is just a failure that happened to me, and it looks very similar to the one you experienced.
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