Are carbon bars dangerous?
01-08-13, 02:36 PM
#76
Senior Member
1+ to all the above
Think of it this way: how in the world does the stem manufacturer (the torque spec numbers are written on the stem) know what handlebar it's attached (or what steerer tube, for that matter)? The torque specs relate to a steel or Ti bolt threading into an aluminum stem and the fact that if the threads are stripped in the stem, there is no way to fix it other than replacement. Unless the handlebar comes with a torque specification, the torque spec is related to the stem only.
I don't own a torque wrench but I do own a couple carbon bikes, including one with a carbon steerer tube. Never needed anything other than an attention to using carbon assembly paste and tightening only as much as necessary.
Think of it this way: how in the world does the stem manufacturer (the torque spec numbers are written on the stem) know what handlebar it's attached (or what steerer tube, for that matter)? The torque specs relate to a steel or Ti bolt threading into an aluminum stem and the fact that if the threads are stripped in the stem, there is no way to fix it other than replacement. Unless the handlebar comes with a torque specification, the torque spec is related to the stem only.
I don't own a torque wrench but I do own a couple carbon bikes, including one with a carbon steerer tube. Never needed anything other than an attention to using carbon assembly paste and tightening only as much as necessary.
It might not be quite so prevalent here, but new people to cycling mechanics have this notion that tighter is better, and that's where the trouble starts with stripped threads and crushed handlebars (both CF and aluminium, steel not so much).
Just think about all those issues people have removing their pedals because a gorilla wrench has been used rather than some deft manipulation of an open-ended wrench or a hex key.
If anything, a torque wrench is useful for "calibrating" a person' estimate of the amount of torque they are applying. They then can relate "red" or "white" or "deep depression" on the skin when using an ordinary wrench or hex key.
I know that until I got a torque wrench, I was under-tightening the bolts on the head plate of the stem when fitting handlebars... but as pointed out earlier, that is not a bad thing, either.
01-08-13, 03:52 PM
#77
Senior Member
The only thing about all this is that if you want a warranty claim on a broken item, then among the first questions that may be asked will be who fitted it, and as a torque wrench used.
It might not be quite so prevalent here, but new people to cycling mechanics have this notion that tighter is better, and that's where the trouble starts with stripped threads and crushed handlebars (both CF and aluminium, steel not so much).
Just think about all those issues people have removing their pedals because a gorilla wrench has been used rather than some deft manipulation of an open-ended wrench or a hex key.
If anything, a torque wrench is useful for "calibrating" a person' estimate of the amount of torque they are applying. They then can relate "red" or "white" or "deep depression" on the skin when using an ordinary wrench or hex key.
I know that until I got a torque wrench, I was under-tightening the bolts on the head plate of the stem when fitting handlebars... but as pointed out earlier, that is not a bad thing, either.
It might not be quite so prevalent here, but new people to cycling mechanics have this notion that tighter is better, and that's where the trouble starts with stripped threads and crushed handlebars (both CF and aluminium, steel not so much).
Just think about all those issues people have removing their pedals because a gorilla wrench has been used rather than some deft manipulation of an open-ended wrench or a hex key.
If anything, a torque wrench is useful for "calibrating" a person' estimate of the amount of torque they are applying. They then can relate "red" or "white" or "deep depression" on the skin when using an ordinary wrench or hex key.
I know that until I got a torque wrench, I was under-tightening the bolts on the head plate of the stem when fitting handlebars... but as pointed out earlier, that is not a bad thing, either.
Also, the torque specs written next to bolts are MAX specifications, not minimums or "numbers to shoot for". Basically, if you go over the specified torque, you might damage the screw threads and no-this-is-not-a-valid-warranty-claim.
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01-08-13, 04:00 PM
#78
Senior Member
I should point out that it makes no sense for the bar manufacturer to assign a "torque spec" to the bars. Torque is something you put onto bolts to produce tension, and of course, the bar manufacturer doesn't know what stem or even what kind of clamping system you are using (2 bolt, 4 bolt, etc.). What the bar manufacturers do instead, most probably, is attempt to design the bar to withstand clamping forces in excess of what stem clamping systems can provide; perhaps even by using published stem max torque specifications as a guide.
This is not to say you use max torque specs for stem bolts as a guide for installing handlebars; after all, what if you are using a Nitto steel stem and the max torque spec is, like 15Nm? Instead, you do what others have mentioned and use carbon assembly paste and tighten minimally until the bars don't rotate when you jump on them.
This is not to say you use max torque specs for stem bolts as a guide for installing handlebars; after all, what if you are using a Nitto steel stem and the max torque spec is, like 15Nm? Instead, you do what others have mentioned and use carbon assembly paste and tighten minimally until the bars don't rotate when you jump on them.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
01-08-13, 04:56 PM
#79
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Torque specs are for the hardware and not the bar. It prevents you from snapping the bolts. Chances are that you'll snap the bolt way before you come close to crushing the bar.
If you've been working on bikes for a while you'll get a feel for how tight a bolt should be. If you are just starting out...get a torque wrench..they don't cost that much.
If you've been working on bikes for a while you'll get a feel for how tight a bolt should be. If you are just starting out...get a torque wrench..they don't cost that much.
01-08-13, 07:11 PM
#80
Senior Member
So, what's the torque spec for a carbon bar? Surely it can't be the number written on the stem, right? Unless the stem and the bar are a matched set, there is no way the stem manufacturer knows what bar you are mating it to. I've never seen a torque spec matched to a handlebar.
Also, the torque specs written next to bolts are MAX specifications, not minimums or "numbers to shoot for". Basically, if you go over the specified torque, you might damage the screw threads and no-this-is-not-a-valid-warranty-claim.
Also, the torque specs written next to bolts are MAX specifications, not minimums or "numbers to shoot for". Basically, if you go over the specified torque, you might damage the screw threads and no-this-is-not-a-valid-warranty-claim.
The clamp on a stem doesn't close entirely up on itself. There should always be a space between the faceplate and the stem.
To achieve the clamping pressure on the bar requires a certain torque spec on the bolts, and it's not to avoid stripping the thread. If you exceed the torque spec, you are pulling the face plate of the stem into the bar tubing, and hence bringing into play a crush force which then breaks the epoxy resin and either displaces or breaks the carbon threads underneath.
There was a celebrated case on the Road Forum last year when a poster detailed how he heard a crushing sound on the CF bar he was installing, and the torque on the faceplate bolts was much less than the spec. And he was using IIRC, a small hand torque wrench designed for doing this work.
Last edited by Rowan; 01-08-13 at 11:11 PM.
01-09-13, 05:39 AM
#82
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01-09-13, 06:42 AM
#83
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01-09-13, 07:16 AM
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My carbon TT bar has a bit of aluminum under the carbon layers in the middle to make it stronger and to allow it to be more tightly clamped.
01-09-13, 11:26 AM
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01-13-13, 05:52 PM
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You realize I'm pretty sure he was being sarcastic and the two of you were being extremely thin-skinned and arrogant?
01-13-13, 07:01 PM
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I live in the center of bike heaven, surrounded by hundreds of bike shops ... and I have yet to witness a pro bike mechanic use his torque wrench to do something as basic as tightening a bolt on a handlebar.
Replacing stem and seatpost binder bolts every couple of years is not a bad idea, either. They fail.
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01-14-13, 12:25 AM
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1+ to all the above
Think of it this way: how in the world does the stem manufacturer (the torque spec numbers are written on the stem) know what handlebar it's attached (or what steerer tube, for that matter)? The torque specs relate to a steel or Ti bolt threading into an aluminum stem and the fact that if the threads are stripped in the stem, there is no way to fix it other than replacement. Unless the handlebar comes with a torque specification, the torque spec is related to the stem only.
I don't own a torque wrench but I do own a couple carbon bikes, including one with a carbon steerer tube. Never needed anything other than an attention to using carbon assembly paste and tightening only as much as necessary.
Think of it this way: how in the world does the stem manufacturer (the torque spec numbers are written on the stem) know what handlebar it's attached (or what steerer tube, for that matter)? The torque specs relate to a steel or Ti bolt threading into an aluminum stem and the fact that if the threads are stripped in the stem, there is no way to fix it other than replacement. Unless the handlebar comes with a torque specification, the torque spec is related to the stem only.
I don't own a torque wrench but I do own a couple carbon bikes, including one with a carbon steerer tube. Never needed anything other than an attention to using carbon assembly paste and tightening only as much as necessary.
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01-14-13, 01:08 AM
#90
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I'd be interested to know how many of you that say you don't trust carbon bars have carbon fork on your bike without giving it a second thought...
Sudden failure of carbon forks or steerer is generally going to be much more likely to injure you than a carbon bar failing.
Me, I happily use carbon bars (and forks).
JMR
Sudden failure of carbon forks or steerer is generally going to be much more likely to injure you than a carbon bar failing.
Me, I happily use carbon bars (and forks).
JMR
01-14-13, 01:28 AM
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Hundreds of miles and thousands of feet climbing/descending with carbon everything on two bikes. Knock on wood perhaps. No issues here. Pretty confident using them. Pro-cycling is too, no?
