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PostPosted: Sat Jun 09, 2012 12:00 am 
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Posts: 65
This comes down to ignorance on my part - freely admit that, anyway:

Deda Presa Carbon bars, paired with a Deda Zero 100 stem for my new bike. Turns out I'd miscalculated the reach a little, so i need a slightly shorter stem. So I order a new stem, but while I wait I figured I had a spare stem of correct length that I could use.

So it turns out Deda's "special" 31.7mm "standard" makes a real difference. The spare stem was a Syntace F109, nice stem, but as you'll see below, it didn't really get along with those Deda bars :( I used carbon assembly compound, used a torque wrench; made sure it was 6nm. Only had the stem on for a 2 days too, one real ride.

Image
Image

So the question is, are these bars now unusable? The indentation is only on the top of the bars, not the same underneath. If you need more pics let me know.

Embarrassing :oops:


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PostPosted: Sat Jun 09, 2012 1:13 am 
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Location: London
Probably better to get a set of alloy bars.

I think it was more down to over torquing, 4-5Nm on a 4 bolt face plate should be fine. I barely go over 4 on a set of alloys


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Posted: Sat Jun 09, 2012 1:13 am 


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PostPosted: Sat Jun 09, 2012 1:35 am 
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roadman wrote:
Probably better to get a set of alloy bars.

I think it was more down to over torquing, 4-5Nm on a 4 bolt face plate should be fine. I barely go over 4 on a set of alloys


Fair enough. I admit i just followed the 6nm listed on the stem.

The impact seems pretty minimal, and I'd love to keep using these bars, but damaged carbon does worry me.


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PostPosted: Sat Jun 09, 2012 2:17 am 
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It's nothing.


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PostPosted: Sat Jun 09, 2012 3:06 am 
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I agree...those bars are fine. I have a Deda Element as well and totally crushed a new Easton EC90 Aero bar...being careful no less! The suggested 6Nm torque is a bunch of $hit. The second EC90 I went 4Nm and was fine.


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PostPosted: Sat Jun 09, 2012 3:24 am 
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looks like the clearcoat chipped off. not structural at all


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PostPosted: Sat Jun 09, 2012 3:26 am 
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If it was crushed, you would know. Carbon doesn't bend or relax, it's either structurally sound or it fails, there is no in-between.
If it's just the thick-ass paint being marred, which is the case, you wouldn't notice a difference in the bars.

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PostPosted: Sat Jun 09, 2012 3:43 am 
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I have almost the same set-up (Deda Presa's with Syntace F119 stem). No problems torqued to 5 Nm. That damage is cosmetic. No worries.


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PostPosted: Sat Jun 09, 2012 3:47 am 
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BTW,

iscarrr wrote:
So it turns out Deda's "special" 31.7mm "standard" makes a real difference.


Nope. :thumbup:

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PostPosted: Sat Jun 09, 2012 4:40 am 
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Location: Sydney, Australia
From what i understand, deda round up to 31.7 and everybody else rounds down to 31.6 but the size is essentially the same.

I also have a set of presa bars with a f109 attached. torqued just past 5nm, it did not make any marks like that.

prendrefeu wrote:
If it was crushed, you would know. Carbon doesn't bend or relax, it's either structurally sound or it fails, there is no in-between.
If it's just the thick-ass paint being marred, which is the case, you wouldn't notice a difference in the bars.


Unfortunately for the OP this doesnt really reflect reality, it would be nice if it did. Being a composite material, it doesnt behave like a metal, ceramic or plastic, and it can fail in different ways. It doesnt have a plastic region like metals, but it also doesnt elastically deform linearly to a failure point like a ceramic. Carbon definitely does bend, look at a windsurfing mast for instance. It is possible for an area of the component to be damaged, with the rest of the structure holding it more or less in place until the damage propogates far enough for it it give completely. When someone breaks a bar (or any other component), chances are that it suffered some kind of damage at one point without the owner knowing. It held together fine for a while, until they ran over a bump or something, and gave it enough load for it to snap. Point is, there is definitely an in-between.

I wouldnt ride it. But its your bar so its your call.


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PostPosted: Sat Jun 09, 2012 5:00 am 
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Location: NYC
We have been over this numerous times....the torque value stamped on stems is MAX allowable torque NOT recommended torque. If u were using carbon paste then u would most likely have sufficient bite at about 4 Nm or even less. I have never had to torque a 4 bolt stem to more then 4Nm and never experienced slipping. Unfortunatetly your bars are toast. EM3

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PostPosted: Sat Jun 09, 2012 8:39 am 
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Thanks for all the input guys. Got a lot of insight from the replies.. wish I'd had that knowledge before i installed the bars!

I looked at the damage a bit more. There's no flaked carbon at all, but if you run your finger over it you can feel some indentation.

Seems like most of you think they'll be fine, but the few of you who don't are doing my head in. I'm leaning towards still using them, and keeping a close eye on the area, but clearly im taking a risk. :oops:


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PostPosted: Sat Jun 09, 2012 12:01 pm 
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In my experience the Syntace stems will do that to bars unless the top bolts are evenly tightened with the bottom. I would take the bars off and flex the hell out of them to see if they creak or crack. If not, then it is probably cosmetic. My guess is that its cosmetic.

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PostPosted: Sat Jun 09, 2012 2:02 pm 
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You can always test it as the aerospace guys do checking composite surfaces.
Tap it with a coin or something and listen. Serious.

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Posted: Sat Jun 09, 2012 2:02 pm 


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PostPosted: Sat Jun 09, 2012 3:04 pm 
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I would remove everything off the bar and look extremely close.
I've had the Presa bar since it's intro that I run w/a Nero Zero stem, I have some markings on the finish but the bar is solid. I find that when using carbon paste you don't want to go to the spec torque. I torque my Presa to 4 w/paste and have never had an issue.
I'd think your bar is structurally fine but you need to make that call...
All that being said, I'll probably never buy another carbon bar, there is just no reason to.


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