# How do you know if you cracked the Carbon Fiber due to overtightening?



## Rexg (Jul 3, 2011)

HI All,

I thought of posting in this forum since I think this may be a noob question. I just installed a new carbon handlebar and of course it being the first time installing one, ive had a few issues along the way. Anyway, my question is, how do I know if I overtightened the stem and damaging the bars? I used a 5nm torque driver and as I was tightening it, i was in a quiet room and heard a soft crackling sound. thinking that i may have crushed the bars even before the 5nm click, i unloosened everything and inspected. i think it may have been the clearcoat as I can see some paint that got scratched. I am hoping it was just the paint and the cf may actually be tougher that what i perceive it to be. Do you think I am just being paranoid? of course i don't want to find out that i have a broken handlebar doing a 35-40mph downhill switchback on a shared road.


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## icsloppl (Aug 25, 2009)

Don't ride it. At all. You can do a search here and on other sites about carbon components and failure modes.

The CF is a fabric. It has no structural strength of its own. The resin gives it its form. You likely just cracked that.

Even if you can place significant force on the compnent today, you have creaed a stress-riser. At some time in the future, the component will fail at that point.

That time is normally the worst possible, such as hitting a pot hole at 40 mph.


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## Rexg (Jul 3, 2011)

yikes. not what i wanted to hear. 100 dollars was a waste then. i tried searching for other posts before even installing and the consensus was that as long as i torqued it to 5nm and under, i am fine. of course i can try sending it back to warranty because i torqued it to spec. if that's the case, all i wasted was a 30 dollars lizardskins bar tape.


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## Camilo (Jun 23, 2007)

Internet experts of course have sure answers for you, but we have no idea w/o looking at the bars. You should have an expert look at the bars, or at the very least post some good quality pictures.

And why would it waste the handlebar tape? Can't you carefully remove it and re-use it? I do that all the time with my inexpensive Deda tape.


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## PJ352 (Dec 5, 2007)

Since you use the word 'know', the only way you'll ever really _know_ if your bar has been compromised is to subject it to an ultrasonic test using what's called an FEM method (basically, an ultrasound). This will 'find' any delaminations or cracks in the CF epoxy.

Just as an aside, unless your torque wrench is known to be accurate, the possibility exists that you applied excessive torque. FWIW, I've done all the work on my bikes since the early 90's (and CF bikes for the last 4 years). Never owned or used a torque wrench and never damaged a part.


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## Kerry Irons (Feb 25, 2002)

*Testing*



Rexg said:


> HI All,
> 
> I thought of posting in this forum since I think this may be a noob question. I just installed a new carbon handlebar and of course it being the first time installing one, ive had a few issues along the way. Anyway, my question is, how do I know if I overtightened the stem and damaging the bars? I used a 5nm torque driver and as I was tightening it, i was in a quiet room and heard a soft crackling sound. thinking that i may have crushed the bars even before the 5nm click, i unloosened everything and inspected. i think it may have been the clearcoat as I can see some paint that got scratched. I am hoping it was just the paint and the cf may actually be tougher that what i perceive it to be. Do you think I am just being paranoid? of course i don't want to find out that i have a broken handlebar doing a 35-40mph downhill switchback on a shared road.


A close visual inspection is certainly in order, and it would not hurt to have a hand-held magnifying glass or some reading glasses to improve your magnification. A way to test for CF damage is to "tonk" the part with a coin or small screwdriver. If there is damage to the CF composite, you will get a change of tone when you hit the damaged portion. You can't spend too much time going over this part!


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## bike981 (Sep 14, 2010)

Wow, considering the posts above, if those were my handlebars, I'd replace them and consider the extra $100 to be a cheap form of insurance against a trip to the ER...


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## PJ352 (Dec 5, 2007)

bike981 said:


> Wow, considering the posts above, if those were my handlebars, I'd replace them and consider the extra $100 to be a cheap form of insurance against a trip to the ER...


That would make two of us, except my replacement would be aluminum.


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## superjesus (Jul 26, 2010)

PJ352 said:


> That would make two of us, except my replacement would be aluminum.


^ This.


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## Rexg (Jul 3, 2011)

here are some pics. notice the indentation of the rough finish. i think this is why it crackled as i could not find any cracks using a jeweler's loupe and i also tried tapping the bar and depressing it and everything looks ok. or i hope it's just my noobish paranoia. i know cf is tough. why would they make planes out of it.


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## PJ352 (Dec 5, 2007)

I don't think everything looks ok. There doesn't need to be visible cracks or crushed tubing for CF's strength to be compromised, but the indentation does signify a level of compression at the clamp. My guess is there was excessive torque applied. 

If it were mine I'd consider it a lesson learned and wouldn't use it.


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## terbennett (Apr 1, 2006)

PJ352 said:


> I don't think everything looks ok. There doesn't need to be visible cracks or crushed tubing for CF's strength to be compromised, but the indentation does signify a level of compression at the clamp. My guess is there was excessive torque applied.
> 
> If it were mine I'd consider it a lesson learned and wouldn't use it.


+1...... :thumbsup:


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## Natedogz (Aug 25, 2010)

terbennett said:


> +1...... :thumbsup:


Yes, and as mentioned things sometimes fail before reaching recommended torque settings, torque wrenches of click and dial type need to be recalibrated at least once per year. Torque specs require a fastener with clean threads and sometimes the part being torqued also requires properly lubed threads or you won't get proper torque. Always use cross pattern bolt tightening too.


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## fuzzy (Jul 19, 2011)

I would at least give them the Bo Jackson stress test before I got rid of them. If they passed I would probably use them....but, I have done a lot of stupid stuff in my time.


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## velocanman (Jul 15, 2011)

FWIW, I agree that the compressive depression in the bar is worth concern. The depth appears to be through the friction coating and clear coat into the tube.

Are you sure that open-face front cap is approved for use on your bars? There are mixed feelings about the cutouts on those front caps for this very reason. I like a solid cap with a nice logo on the front of it.

I applaud your use of a torque wrench, but wonder what method you used to tighten. Did you "walk around" the four bolts, evenly tightening them until reaching 5 Nm? What type of torque wrench do you use--an adjustable one or the small Ritchey "clicker". It looks like you over-tightened the top bolts, pushing the cross-brace of the front cap into the bar.

Is there a similar depression on the underside of the bar, coinciding with the lower cross brace on the front cap? If not, you may have clamped down out-of-round, causing a pinch at the top.

EDIT: I was reminded of a similar concern with cutouts on the steerer tube clamp of the stem, and one or more manufacturers that do not approve use of those on their carbon steerer tubes. Also note the common practice to put a short 1/8" spacer on top of the stem to allow the steerer tube to pass through the stem completely. These are all to prevent crushing and crimping the steerer tube which can lead to failures like George Hincapie suffered in Paris-Roubaix.

I wouldn't ride it.


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## velocanman (Jul 15, 2011)

I just made some edits to my previous post. You might have to refresh to see them.


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## Optimus (Jun 18, 2010)

Ouch ... I would take that bar off as fast as I could. Definitely not worth the risk!


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## PJ352 (Dec 5, 2007)

velocanman said:


> EDIT: I was reminded of a similar concern with cutouts on the steerer tube clamp of the stem, and one or more manufacturers that do not approve use of those on their carbon steerer tubes. Also note the common practice to put a short 1/8" spacer on top of the stem to allow the steerer tube to pass through the stem completely. These are all to prevent crushing and crimping the steerer tube which can lead to failures like George Hincapie suffered in Paris-Roubaix.


As the link provided will show, you're right that some manufacturers recommend against using the stem design you describe, but re: spacers atop the stem, the link also recommends against their use with (in this case) Specialized CF forks, because of the use of a long expander plug (versus compression plug). IIRC, some C'dale models and Giant does the same. There also are variances in the max _number_ of spacers recommended. 

Since designs/ recommendations vary, I'd advise that the specific fork manufacturers installation instructions be followed.

http://service.specialized.com/coll...Fork---Carbon-Road-Fork-Instruction-Guide.pdf


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## Rexg (Jul 3, 2011)

yup. its off my bike already. taking it off last night to take a pic and putting it back on to torque crushed the bar. what a short life for this bar. it was just made 10 days ago according to the label. or thats what the label stated. oh well. back to aluminum.


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## RickRandhawa (Jul 26, 2011)

Rexg said:


> yup. its off my bike already. taking it off last night to take a pic and putting it back on to torque crushed the bar. what a short life for this bar. it was just made 10 days ago according to the label. or thats what the label stated. oh well. back to aluminum.


How sad :/

Your thread just talked me out of some CF handlebars. Thank you!


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## Mr. Versatile (Nov 24, 2005)

Some parts work great & are desirable in carbon fiber, Some don't. Handlebars & stems in CF just aren't trustworthy enough for me to use them. Besides, they don't even weigh significantly less that alloy.


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## Rexg (Jul 3, 2011)

My stem came with my bike which is a most tigermax so i hope this wont dissapoint me. Ill probably get a new al bar and possibly a stem when i do my retul fit since i have this persistent right knee pain even if i already had a static fit. Glad to have helped others in realizing that cf bars are not exacly a good idea. Oh yeah i used a ritchey torque key to torque. Now im scared to use it to adjust my seatpost.


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## The_real_maverick (Sep 25, 2011)

Ya, frame and seat post are useful for CF, but bars I wouldn't


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## vladvm (May 4, 2010)

first tell tale is you "heard a crack", second is you see visual evidence of the crack... it's done. don't use it and replace. lesson learned.

properly installed, you will not hear or see anything wrong.


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## Carbon_NiHM (Sep 4, 2011)

It's just delamination of the resin underneath, it will happen causing the fiber cloth to stray away form the resin, due to impacts.

Don't worry about it! Just a cosmetic  until you see a layer of the resin cracking then add some epoxy to fill it in (carbon specific if you must) .

Have fun!


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