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3TTT Death Stem

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3TTT Death Stem

Old 11-25-17, 08:08 PM
  #1  
taguy4
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3TTT Death Stem

I know AVA stems have the reputation of being the famous "death stem" but check out the end of this 3TTT aero stem:
If this isn't an accident waiting to happen I don't know what is! Some shyster eBay seller was actually passing this off as a good stem. Are failures like this a problem with 3TTT stems also? They seem to share the same double slit expansion area with sharp corners at the top of the slits as AVA death stems do.
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Old 11-25-17, 08:15 PM
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Id like to think half the time its the owner/mechanic or whoever is installing the stem overtightening causing it to crack.

Now i gotta go check all my stems.
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Old 11-25-17, 08:33 PM
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It's ugly but I doubt it might cause an accident. Probably the stem would just feel loose and you would check it up.
What i fear most is the handlebar clamp or handlebar breaking suddenly.
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Old 11-25-17, 08:41 PM
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That's not safe to ride. All those stems without a stress-relieving hole at the end of the expansion slot risk those cracks.
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Old 11-25-17, 08:50 PM
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What I think is the main cause of such failures is any extreme torque that is transmitted from stem to steerer, as when a bike is crashed or when someone tries to forcibly twist out a stuck stem.


The sort of shear forces generated in the quill by such causes will greatly stress the quill at the top of the slot, and the crack can be seen to follow just such a path of maximum shear stress.


Having seen how the walls of a house fail from shear stress during an earthquake, and having studied statics and mechanics of materials, leads me to such a conclusion. The concentration of stress at the top of the slot could have been reduced by even a small radius if the stem's maker had figured on whatever caused this stem to fail, but the history of this item is unknown and it very well may have been seriously abused.
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Old 11-25-17, 09:16 PM
  #6  
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The gouging was of not help, time to dress the inside of the steerer.
Beyond that, I have on a few of my stems drilled with a drill press or vertical mill a hole of about 3mm (1/8") to obliterate the sharp slot end. Just makes sense. Not that hard to do.
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Old 11-25-17, 09:53 PM
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.
...alloy stems are not forever. The AVA ones had a bad period where they were very poor and thinned castings.
But I think I've seen at least one busted stem from all the more common manufacturers...especially if you include failures at the bar clamp area.
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Old 11-25-17, 10:12 PM
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Speaking of bad designs, I have an AVA stem on one of my Peugeots that has an oval cutout in the front of it's handlebar clamp to let the handlebar show thru; I've always thought that was a bad design, too, but it's managed to hold up since 1976. I would like to change it, though, for a more substantial looking stem at some point.

Getting back to the 3TTT stem above, I wouldn't want to be going very fast and turning a corner when that piece breaks off and the stem comes loose in the steerer tube. Something tells me that wouldn't be a good situation to be in. If it broke while going slow and without any traffic around it might not be a catastrophe.
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Old 11-25-17, 11:29 PM
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That stem is toast. Don't ride it if you don't want to die.
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Old 11-25-17, 11:56 PM
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My take? Retire that stem but don't sweat it. It was highly unlikely to get worse as long as it was sitting in the steerer undisturbed. Putting it back in and re-using it is iffy so I wouldn't. And I would chalk it up as a "good" failure. Any failure you detect at your workbench, vs on the road, is, in my book, a good failure.

Edit: I've never thought to study the slots on the TTT stems I've owned. Likely many had that same square detail. Never broke one and I used some of them many miles. My Peter Mooney went 25,000 plus miles on a new TTT bar and stem. I retired them because they had seen a couple of hard crashes. (I was worried more about the handlebars.) That said, I will have to look at all my stems and their slots. (My Nittos use wedges which has always struck me as a better system in addition to being easier to make. Among other things, diameter and fit tolerances matter far less with a wedge.)

Ben

Last edited by 79pmooney; 11-26-17 at 12:05 AM.
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