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Main
Date: 14 May 2007 09:18:01
From: Ron Ruff
Subject: Another broken Ritchey crank...
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http://www.whitemountainwheels.com/blog/wp-content/uploads/2007/05/RitcheyPro1-.jpg
I inspected them right before leaving for Gila, and didn't see
anything unusual... but a mile from the finish on stage 3 the left arm
snapped when I stood up. They had ~ 13,000 miles. No racing and hardly
any sprinting on them either before Gila.
Yes I crashed. It was right after a sharp turn though, so I was going
less than 20mph and wasn't hurt badly... made it in on one leg. John
Verheul loaned me the DA arm off his TT bike so I could continue the
suffering...
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Date: 15 May 2007 09:51:22
From: landotter
Subject: Re: Another broken Ritchey crank...
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On May 14, 11:39 pm, carlfo...@comcast.net wrote:
> On 14 May 2007 21:23:34 -0700, landotter <landot...@gmail.com> wrote:
>
>
>
> >On May 14, 8:30 pm, jobst.bra...@stanfordalumni.org wrote:
>
> >> If you look at the failure pictures at:
>
> >>http://pardo.net/bike/pic/fail-001/FAIL-001.html
>
> >Jobst,
>
> >One of the pictures mentions "vanity grooves" in tandem with strap
> >wear as a cause of failure. Nothing to do with the OP, of course, but
> >care to enlighten us to what a "vanity groove" is? I'm assuming it's
> >not a dance track released by a celebrity, but I've been known to be
> >pretty slow...
>
> >thnx,
> >Max
>
> Dear Max,
>
> Take a normal rounded crank, roughly oval in cross-section.
>
> Now remove a wide groove of material from the side.
>
> Stamp "Colnago Ernesto" in the groove.
>
> The groove looks different, saves a few grams of weight that don't
> matter, lets the manufacturer display a name, and seems to lead to
> dramatic failures, so "vanity groove" is a good description.
>
> http://pardo.net/bike/pic/fail-001/crank-fail-013-014.jpg
D'oh!
That's pretty obvious, now that ya mention it. One of my tri-weekly
bikes has some vintage Suntour cranks circa '78 that have a vestigal
vanity groove. It's only a mm deep and ~7mm wide. Perhaps one of their
engineers figured that this was as much vanity as was sensible to risk.
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Date: 14 May 2007 21:23:34
From: landotter
Subject: Re: Another broken Ritchey crank...
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On May 14, 8:30 pm, jobst.bra...@stanfordalumni.org wrote:
> If you look at the failure pictures at:
>
> http://pardo.net/bike/pic/fail-001/FAIL-001.html
>
Jobst,
One of the pictures mentions "vanity grooves" in tandem with strap
wear as a cause of failure. Nothing to do with the OP, of course, but
care to enlighten us to what a "vanity groove" is? I'm assuming it's
not a dance track released by a celebrity, but I've been known to be
pretty slow...
thnx,
Max
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Date: 15 May 2007 06:15:52
From:
Subject: Re: Another broken Ritchey crank...
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Max Landotter writes:
>> If you look at the failure pictures at:
http://pardo.net/bike/pic/fail-001/FAIL-001.html
> One of the pictures mentions "vanity grooves" in tandem with strap
> wear as a cause of failure. Nothing to do with the OP, of course,
> but care to enlighten us to what a "vanity groove" is? I'm assuming
> it's not a dance track released by a celebrity, but I've been known
> to be pretty slow...
The groove in the middle of the face of the crank reduces the
torsional strength by about 50%. You'll note that Shimano and
Campagnolo ceased machining these groves on their cranks a few years
ago. Other manufacturers didn't catch on and make U-channel shape
cranks that are even weaker in torsion and lateral bending.
The groove has no positive function but people liked its looks.
Therefore "vanity groove".
Jobst Brandt
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Date: 15 May 2007 05:17:35
From: Ted Bennett
Subject: Re: Another broken Ritchey crank...
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landotter <landotter@gmail.com > wrote:
> jobst.bra...@stanfordalumni.org wrote:
>
> > If you look at the failure pictures at:
> >
> > http://pardo.net/bike/pic/fail-001/FAIL-001.html
> >
>
> Jobst,
>
> One of the pictures mentions "vanity grooves" in tandem with strap
> wear as a cause of failure. Nothing to do with the OP, of course, but
> care to enlighten us to what a "vanity groove" is? I'm assuming it's
> not a dance track released by a celebrity, but I've been known to be
> pretty slow...
>
> thnx,
> Max
It's a relative of drillium. I would propose the name millium, material
which has had grooves milled in its surface.
In an attempt to make cranks lighter, some were milled along their outer
face. The vanity comes in when you contrast the extra speed the
reduction in weight gives you, to the higher risk of breakage. The
amount of risk versus speed is something not easy to settle, but it's
not difficult to envision the result of a broken left crank as you
accelerate hard beside a big truck.
--
Ted Bennett
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Date: 14 May 2007 22:39:25
From:
Subject: Re: Another broken Ritchey crank...
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On 14 May 2007 21:23:34 -0700, landotter <landotter@gmail.com > wrote:
>On May 14, 8:30 pm, jobst.bra...@stanfordalumni.org wrote:
>
>> If you look at the failure pictures at:
>>
>> http://pardo.net/bike/pic/fail-001/FAIL-001.html
>>
>
>Jobst,
>
>One of the pictures mentions "vanity grooves" in tandem with strap
>wear as a cause of failure. Nothing to do with the OP, of course, but
>care to enlighten us to what a "vanity groove" is? I'm assuming it's
>not a dance track released by a celebrity, but I've been known to be
>pretty slow...
>
>thnx,
>Max
Dear Max,
Take a normal rounded crank, roughly oval in cross-section.
Now remove a wide groove of material from the side.
Stamp "Colnago Ernesto" in the groove.
The groove looks different, saves a few grams of weight that don't
matter, lets the manufacturer display a name, and seems to lead to
dramatic failures, so "vanity groove" is a good description.
http://pardo.net/bike/pic/fail-001/crank-fail-013-014.jpg
Cheers,
Carl Fogel
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Date: 14 May 2007 19:41:52
From: jim beam
Subject: Re: Another broken Ritchey crank...
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Ron Ruff wrote:
> http://www.whitemountainwheels.com/blog/wp-content/uploads/2007/05/RitcheyPro1-.jpg
predictably...
>
> I inspected them right before leaving for Gila, and didn't see
> anything unusual... but a mile from the finish on stage 3 the left arm
> snapped when I stood up. They had ~ 13,000 miles. No racing and hardly
> any sprinting on them either before Gila.
>
> Yes I crashed. It was right after a sharp turn though, so I was going
> less than 20mph and wasn't hurt badly... made it in on one leg. John
> Verheul loaned me the DA arm off his TT bike so I could continue the
> suffering...
>
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Date: 14 May 2007 12:45:52
From: Donald Gillies
Subject: Re: Another broken Ritchey crank...
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These cranks are junk. The firesale clearances of these cranks proves
it. Girder structures apparently do not handle torsional stresses
very well.
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Date: 15 May 2007 01:30:12
From:
Subject: Re: Another broken Ritchey crank...
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Donald Gillies writes:
> These cranks are junk. The firesale clearances of these cranks
> proves it. Girder structures apparently do not handle torsional
> stresses very well.
They handle neither torsion nor lateral bending, the most common
failure mode for cranks. This is mainly because most cranks are 8x
stronger as levers in the plane of rotation than they are in lateral
bending, the type of loading ignored by most crank designs.
If you look at the failure pictures at:
http://pardo.net/bike/pic/fail-001/FAIL-001.html
You'll see typical lateral failures, like the one to which you refer:
http://tinyurl.com/2w5eep
Jobst Brandt
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