After Eric's and Grant's responses, I went back downstairs and took a long hard
look at things. I removed the right rear brake pad and found a strange groove
cut into it, about the width of the failed rim piece. I tried to take a photo,
but it doesn't show up well. The other interesting thing, I found a 2 mm bulge
mid-way along the length of the failure directly next to a spoke nipple hole on
the braking surface of the rim. The spoke and the nipple appear to be in proper
condition, not loose, no cracks around the nipple hole. There are no other such
bulges anywhere on either side of the rim. The bulge is not on a weld joint,
either. I don't know what, but this has got to mesan something. Oh, and I used
a glass to closely inspect the brake pad. no foreign objects embedded in the
compound. Also, the sidewall of the Pasella has no evidence of the compound
having rubbed into it and caused the blow out. Anyone out there got any
thoughts on this?
________________________________
From: Ray Shine <r.sh...@sbcglobal.net>
To: rbw-owners-bunch@googlegroups.com
Sent: Sun, December 4, 2011 7:16:48 PM
Subject: Re: [RBW] Re: Near-Catastrophic Rim Failure
Well, kind of glad to hear that -- only 15. I need a new rim now anyway, so
maybe I'll BART out and show you guys the wheel and the failed section pretty
soon. You guys -- and maybe Rich -- might offer a conclusion that would
benefit
some other folks on this list. (By the way, I'm not suggesting definitively
that
Rich built this wheel. I actually don't recall where I got it.)
________________________________
From: grant <grant...@gmail.com>
To: RBW Owners Bunch <rbw-owners-bunch@googlegroups.com>
Sent: Sun, December 4, 2011 6:25:09 PM
Subject: [RBW] Re: Near-Catastrophic Rim Failure
I've seen maybe fifteen rims fail this way, and ever time it's been
caused by rock-wear, as Eric suggested. That's not to say nothing else
can cause it, but that is (in my experience) the most common (100
percent) reason for it. Rim makers and tire makers build more wiggle-
room into their stuffs than...an extra five psi. Close inspection
would tell the story---whether the chunk-o-rim just blew out suddenly
("catastrophically" means suddenly and complete, in this context), or
whether the rim had been scored deep by Foreign Object for a while,
and just couldn't take it anymore.
Conzelman (note spelling) is a beautiful road, as neat as any in
California (maybe the world). Too short, one way, and what a
dropoff.Glad you're OK, Ray.
On Dec 4, 4:35 pm, Ray <r.sh...@sbcglobal.net> wrote:
> Took a nice ride across the bridge and up to Hawk Hill, planning to
> get home in time to catch the 49er game at the end of 1st quarter. I
> didn't make it. My rear rim blew out as I took a slow (translated:
> continuous braking down 18% descent to hold speed at 10(-)mph.)
> descent down back side of Conzumel Road toward the lighthouse.
>
> Because I crashed on the same section of this road in January and
> broke my collarbone, I have been taking this descent extra carefully
> and slowly now that I am back on the bike. Just as I was in the last
> tight turn before the road levels out to a reasonable grade, my rear
> tire popped and blew out.
>
> I managed to stay upright and bring it to a stop against a bank.
> There, I discovered that my rear rim blew out and a 18" section of the
> sidewall bead just blew out and tangled up in the spokes and
> chainstay. The wheel rims are Araya. Just prior to leaving home, I
> pumped up the rear Pasella x32 to 85 pounds. The wheels are about
> three years old. No prior wheel trauma.
>
> Could this failure resulted from the long braking over-heating the rim
> and the pressure blowing it out? Seems strange, but, can that happen?
>
> Here are the pix:
>
> http://www.flickr.com/photos/8581354@N03/sets/72157628281638979/with/...
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