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Old 11-29-05, 09:01 PM   #1
TallRider
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flexing aluminum drop bars - dangerous?

I recently picked up a cheap but new Modolo X-Tenos 8-bend handlebar. It's nice and light, and when I mount brake hoods on it, and lean a bit on them, the bar flexes a fair bit. Sure, all road bars flex when you do this, but this one flexes more than my others (Cinelli Giro, Nito B115, Nashbar random Taiwanese ergonomic bend). The question is: is this a danger for breaking while riding? I don't stand and sprint much, but I'm 6'5" and 185# and would like to have the peace of mind that when I do sprint, even if infrequently, the bar will be okay. What do you think? It's 44cm.
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Old 11-29-05, 09:05 PM   #2
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Along with "nice and light" comes flexibility. The bar probably isn't a danger for breaking in the near future but, at your weight, I wouldn't plan on using it for years.
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Old 11-29-05, 09:36 PM   #3
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Originally Posted by HillRider
Along with "nice and light" comes flexibility. The bar probably isn't a danger for breaking in the near future but, at your weight, I wouldn't plan on using it for years.
I ride with TTT 199's. I'm 175. Nice and light - no flex at all. I'd be suspicious of the ones you're talking about.
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Old 11-29-05, 10:01 PM   #4
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I've heard that the Modolo bars (and stems) do have quite a bit of flex to them. I've got a 6 bend Modolo that I've yet to use so can't say anything personally yet.
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Old 11-29-05, 10:49 PM   #5
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Yeah, I've snapped two Modolo stems. They drilled that big hole down the quill to get the deeply-recessed bolt. Problem is, they made the wall thickness way too thin as a result... SNAP!

On the bars, inspect them about once a year where they clamp into the stem. Pull them out and clean it up to see the edge where they go into the stem. They'll start cracking at that spot on the bottom where you can't normally see it... I've snapped a bar in a sprint once... luckily the other half stayed in the stem...

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Old 11-30-05, 12:05 AM   #6
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On the bars, inspect them about once a year where they clamp into the stem. Pull them out and clean it up to see the edge where they go into the stem. They'll start cracking at that spot on the bottom where you can't normally see it... I've snapped a bar in a sprint once... luckily the other half stayed in the stem...
So, when a bar breaks, it's likely to do so near the steam? That's kind, I guess. Easy to check up on compared to somewhere under the bar tape. Thanks for the info. And the story. That's pretty scary - bar and stems both.
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Old 11-30-05, 02:30 PM   #7
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Originally Posted by timcupery
So, when a bar breaks, it's likely to do so near the steam?
Yup, there's where a stress-riser occurs. This is cause by high-torque due to the long moment-arm with the force starting at the handlebar ends and the pivot at the stem. The stress is concentrated on the edge of the stem where the bar first goes in. This is the transition point for flex vx. zero-flex of the material. It's like hammering a nail halfway into a 2x4. Then bending the exposed half with pliers until it breaks. It will usually break within a millimeter or two from the point where it sticks into the wood.
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Old 11-30-05, 02:55 PM   #8
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Originally Posted by DannoXYZ
Yup, there's where a stress-riser occurs. This is cause by high-torque due to the long moment-arm with the force starting at the handlebar ends and the pivot at the stem. The stress is concentrated on the edge of the stem where the bar first goes in. This is the transition point for flex vx. zero-flex of the material. It's like hammering a nail halfway into a 2x4. Then bending the exposed half with pliers until it breaks. It will usually break within a millimeter or two from the point where it sticks into the wood.
The physics of this all make sense. The reason I'm asking is because the Modolo 8-bend bars seem to be flexing at one of the upper bends, not at the stem. Though I'll have to test this again and have one of my housemates watch.
Are you in physics or engineering stuff? My last class in either of those disciplines was spring 1999, though I've kept fresh by testing prototype running shoes.
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Old 05-25-07, 05:00 AM   #9
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dangerous stems

hello, i read an article about dangerous stems by mr. John S. Allen called "split handlebar stem extensions are dangerous". that tells enough. i hope it helped you in convincing to avoid these stem-systems. nice greetings , sjaak!
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Old 05-25-07, 05:53 AM   #10
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hello, i read an article about dangerous stems by mr. John S. Allen called "split handlebar stem extensions are dangerous". that tells enough. i hope it helped you in convincing to avoid these stem-systems. nice greetings , sjaak!
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