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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...
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.
> 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...
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...
>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.
> 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.
> 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".
> >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.
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.
