Normal for carbon bars to develop slight indent?

[weaponsgrade]

Is normal for carbon bars to develop a slight indentation from the stem clamp? I was playing around with my setup the other day and had the handlebars off. When I run my finger over the clamp area I can feel a very slight depression. There are no cracks, no noises, and no changes in tone when I tap on the area. I always used a torque wrench and if anything the bolts were under-torqued. The bars specify a torque of 6 N-m, but were torqued only to 5 N-m.

[FlashUNC]

Indents are usually bad.

[HenryA]

Hard to tell without seeing it. But, the resin that binds the fibers may have some creep or compressibility that would account for a "slight indent" from clamping. If you think about the carbon bars as made to be strong along their length and not so much in the other direction (across the diameter of the tube) this makes sense.

The benefit of carbon fiber comes from the fibers working in tension where they are extremely strong by resisting stretching in tension. In a lay up with all the fibers running in one direction, at 90 degrees to that directional layup you have only some plastiky glue holding a bundle of fibers together and no real strength in that bundle across the bundle but that of the resin or binder. Of course composite structures would be engineered to provide adequate stiffness or strength in any and all directions where they would be expected to perform, so its not exactly a simple answer.

A nick (cutting fibers) is definitely a sign of the possibility of an impending failure or the chance for one to begin. A "slight indent" maybe not.

[rburnham13]

Unless that "indent" was there when they were new, I would be concerned. Especially if you are a bigger stronger rider. You may put some force on those bars. If they are getting an indent, they are weakening. Carbon, all though strong, has a relatively short life span.

[Black Dog]

Unless that "indent" was there when they were new, I would be concerned. Especially if you are a bigger stronger rider. You may put some force on those bars. If they are getting an indent, they are weakening. Carbon, all though strong, has a relatively short life span.

Carbon has an unlimited lifespan if not stressed beyond its limits. It will withstand unending duty cycles in theory. In practice this may not be the case. Frames and forks made from carbon will wear out a test rig long after their metallic counterparts have failed. The failure mode can be very unpleasant and in the pursuit of lightness durability may be sacrificed. Any damage must be treated seriously. However, a small indentation in the resin is not a big deal as long as the underlying fibres are intact. Resin is flexible and will compress to some degree. All of this from a guy with steel and Ti bikes and the only carbon being on one set of forks and one set of cranks.

[John H.]

What bars?
Was the indentation in the "rough" coating that most makers put on the clamping surface?
That stuff does compress and take on the shape of the stem.

[Cicli]

What bars?
Was the indentation in the "rough" coating that most makers put on the clamping surface?
That stuff does compress and take on the shape of the stem.

I had some Ritchey bars that did that. The slip resistant coating compressed a bit while the bars were fine.

[vqdriver]

tough to speak in generalities without seeing it. but i think i know what the op is referring to and if it's what i think it is, john h is correct. there's some sort of clear resin plastic stuff that i don't know the technical term for. this can take on an impression of stuff clamped to it at proper torque, stems being one of them. if it has the rough portion for clamping friction, i'm not sure you could avoid leaving an impression actually. i've seen some where it looks like fully cured glue oozed out from the stem edges. as long as the fibers are good, i wouldn't worry.


if you feel uneasy about it, you could always try to capture it in a pic and send it off to the maker.

[SoCalSteve]

Unless that "indent" was there when they were new, I would be concerned. Especially if you are a bigger stronger rider. You may put some force on those bars. If they are getting an indent, they are weakening. Carbon, all though strong, has a relatively short life span.

Where are you getting your information from? Love to know....:confused:

[Dead Man]

I found an "indentation" in the exact shape of my stem on a carbon steerer that kinda freaked me out. But then I put it back on the bike, and have even crashed a couple times since then. Hasn't broken!

I did a strength test on some carbon tubing, once... I am a very small rider, so when I cut a fork steerer, I get a pretty good chunk off it. I beat and hammered and torqued and crushed that thing for days - when I finally did get it it to collapse, I still couldn't get it to sheer off. I had to smash it into a pulp before I could actually break off a piece of the tube, and still had to use a bench vise and vise grips. Those carbon fibers are really strong, and cracks don't make the whole matrix explode, like a lot of dudes seem to think.

At least in the EC90 SLx tube I played with.

[lhuerta]

Is normal for carbon bars to develop a slight indentation from the stem clamp? I was playing around with my setup the other day and had the handlebars off. When I run my finger over the clamp area I can feel a very slight depression. There are no cracks, no noises, and no changes in tone when I tap on the area. I always used a torque wrench and if anything the bolts were under-torqued. The bars specify a torque of 6 N-m, but were torqued only to 5 N-m.


this post is pointless without pics...

Minimal/shallow indentations left by stems are harmless, however deeper indentations that have cut beyond the clear coat and pressed deep into the epoxy and resin that binds the carbon fibers, can be damage of concern. One way to tell whether the indent is deep enough to be concerned about, is to look for white/gray clouding in the underlayer of the epoxy. The clouding is an indication that the resin which is impregnated in to the fibers has been compromised. However, the extent to which such damage can compromise the structure is not known...which in the end means ride at your own risk.

BTW, I have never seen a carbon bar stamped with a suggested torque value....are u sure the value u are referencing isn't the max torque value for the stem bolts. The max torque values u see stamped on stems (and other parts) should not be confused with recommended torque....such are the max torque at which the BOLT will fail and have nothing to do with recommended torque values for mating a stem to bar. IME, I have never needed more then 4 Nm to fix a 4 bolt stem face plate to a stem.

[weaponsgrade]

Here are two pics of the bars. It's hard to tell, but in one of the pics you can see a faint circular outline of the stem. If you run a finger over it, you can feel a slight depression. In the other pic you can see the max torque values for 2 bolt vs 4 bolt stems. For the four bolt stem (which is what I have), the max is 6NM.

[lhuerta]

.....those appear perfectly fine, ride in good health and with confidence ! The slight indent appears to be only on the grit coat that is added at the clamp section. Before reinstalling your stem b sure to lightly sand all the inside edges of your stem to remove any sharp or uneven edges. Also use criss/cross pattern when torquing bolts. Lastly the torque value indicates MAX torque not recommended torque,....apply the minimum amount of torque needed to hold bars firmly, which in most cases will be about 4 Nm.

[weaponsgrade]

Cool, thanks. I torqued to 4Nm this time.

[rburnham13]

Where are you getting your information from? Love to know....:confused:

Apparently you have never seen carbon failure? I work in a shop that has seen the highest amount of failed carbon bikes (from Cannondale) in the entire country. Myself and the service manager have helped Cannondale to find its weak spots and fix the issue. We also have a very talented local guy who builds carbon race car bodies and boats. He has gotten into fixing frames, and even wheels. He has shared a lot of his knowledge with us and from I have learned, if it looks a little "sketchy" on the outside, it's probably worse on the inside. Carbon does have a lifespan, especially if worked over and beaten like a bicycle.
In this case, without seeing a pic, if the bars never had an indent to begin with, they should not have one now.

[rburnham13]

Those pics look fine. The only concern is the clear coat is being eaten away by corrosion. Totally normal, and should be fine for a while. Those outlines don't look like cracking to me.

[Cicli]

Those pics look fine. The only concern is the clear coat is being eaten away by corrosion. Totally normal, and should be fine for a while. Those outlines don't look like cracking to me.

Corrosion? :confused:

[marciero]

Those look better than the ones I replaced. Mine also did not pass the "tap test" suggested by LBS-if the sound when tapped lightly with a screwdriver is different in the affected area; eg, deader or less resonant, it can indicate that the fibers are compromised. I am done with carbon bars. For me, they make no sense at all. I still have carbon forks on a couple of bikes though.

[Fatty]

If in doubt , change it out. Just made that up. Seriously though I would bin those.
Run carbon bars on my mountain bikes, all Easton. I inspect them regularly and have never found any kind of dents or depressions in the stem clamping area.

[HenryA]

I'd ride 'em. I'm pretty sure that if you took them off and replaced with new bars, that in a week the new ones would look just like that.

[binouye]

When I changed stems on one of my bikes last year the 3T carbon bars had a slight indent in the rough clamping area, looks/sounds like those bars. They were installed with carbon paste, a matching 3T stem, torque wrench to only 4.5 nm. No other signs that the carbon was compromised at all, so I installed them in the new stem, again with carbon paste and about 4 nm on the torque wrench -- fine so far. I'm guessing the indent is only in the thicker layer of textured resin at the clamping area.

[Louis]

I would not worry about it in the least, and would gladly ride something like that.

I would not want a brand-new pair of bars to have that, but if I rode some for a month then took them apart to discover that sort of "ridge" I wouldn't be surprised or concerned.

If you have busted fibers that's a different story, but as best I can tell that is not the case here.

[rburnham13]

Corrosion? :confused:
Have you never seen a clear coat be eaten away by corrosive salt, from sweat or ocean air? I am located on the seacoast and the salt air combined with people that are heavy sweaters, I have seen many carbon clear coats be eaten away. Even on the likes of Parlee's. The clear coat is another layer of protection, so maybe not super detrimental, but not good in any case.

[bshell]

I'm genuinely curious because I thought clear coats were purely cosmetic.

I've wet sanded the clear coat/logos off of several carbon items (proceed to 1200 grit) assuming that they had no protective/structural value whatsoever.

It leaves a beautifully smooth matte finish.

Carbon builders, care to chime in?

Thanks!

ps. I live by the beach in California and have never had any type of clear coat affected by sweat or ocean air.

[lhuerta]

Oye!

Carbon, all though strong, has a relatively short life span.

Compared to what? Under what conditions? Are you saying that carbon loses its working strength at a higher rate, over time, compared to steel, Ti, Alum?

You need to do some homework on new fibers, resins and epoxy that are being used today.

Carbon does have a lifespan, especially if worked over and beaten like a bicycle..

Every material has a working lifespan, but I have not seen any evidence that carbon fiber has a working lifespan that is less than steel, Ti or alum.

The only concern is the clear coat is being eaten away by corrosion.

That is NOT corrosion... the pics only show the result of grit layer being pressed by stem.

[Louis]

Compared to what? Under what conditions? Are you saying that carbon loses its working strength at a higher rate, over time, compared to steel, Ti, Alum?

Agreed. If it were true there are some folks in military and commercial aircraft who are in for a big surprise some time soon.

[rburnham13]

In theory, carbon should last forever. Theory is not reality. The layers of carbon can start to fail over years of stress at the high stress points, IE bottom bracket, and head tube. I have seen many carbon frames crack in high stress areas. It is not always from impact or abuse. I chalk most of it up to poor manufacturing and the quest to make everything lighter. I have seen numerous Cannondale frames brake near the BB on the seatube. I have seen one completely sheer from an unnoticed crack. When one of these frames was being repaired I got to see wheat the inside of the area looked like. According to the carbon repair guy (a man that builds race car bodies and racing boats), it was built poorly, and considering the application, it should have been much thicker in that area.
When carbon is built well, and sees no abuse aside from what it was engineered for, it should, in theory last forever. Not always the case. In turn, yes carbon has a lifespan.
The military and airline industry is not always trying to cuts cost and weight in the goal of making more money from their products (airline do some for fuel savings, but not at the risk of safety). I feel they are probably building things to a higher standard than bicycle companies. Bicycle companies only care about cranking out high numbers and profit. Maybe, a smaller company that lays their own carbon, would produce a better product, but in my years in the industry and working at shops, I have seen way to many frames crack, and brake to say that carbon does not have a life span.

[Louis]

So, it sounds to me like you're saying that poorly designed and built CF frames are more likely to fail.

I agree, and would add that one could say that about any structural material out there.

[HenryA]

So, it sounds to me like you're saying that poorly designed and built CF frames are more likely to fail.

I agree, and would add that one could say that about any structural material out there.


Yes to all the above.

When carbon fiber frames first showed on the market there were lots of failures and from many different causes for quite a while. It was a mess.

And I would not include any mass market bike in the discussion about the technical characteristics of carbon fiber. There are many, many combinations of fibers, the matrices that hold them together and building and engineering techniques. Properly done, a CF part can have tremendous service life.

Here is an informative article:

http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/6810/Boeing-Carbon-Fiber-and-Engineering-the-Future-of-Aviation.aspx

[drgonzo]

I'm reviving this thread because when I took the bars off a bike last night, I came across the indents you see in the photos. The bars were new when first installed, attached to a Fizik Cyrano R1 stem, have always been properly torqued to 5Nm and tightened in an X pattern to ensure even distribution of force.

The question is, are these bars hosed? They feel fine, there's no creaking or other anomalies.

[jpritchet74]

that doesn't look good to me

[marciero]

I'm reviving this thread because when I took the bars off a bike last night, I came across the indents you see in the photos. The bars were new when first installed, attached to a Fizik Cyrano R1 stem, have always been properly torqued to 5Nm and tightened in an X pattern to ensure even distribution of force.

The question is, are these bars hosed? They feel fine, there's no creaking or other anomalies.

That's the thing with carbon. You're not going to get any warning when they fail. For god's sake dont ride those.

[R3awak3n]

yeah, that does not look good. I would not ride those.

[Tickdoc]

I look at indented bars every time I ride my seven...bought the bars used off my wrench. 3t ergo nova. Had them on for about 5 years now...been through two stems ridden across three states and thousands of miles.

https://i.imgur.com/RlcVUFW.jpg

[Duende]

That doesn’t look good to me either. FWIW, I had small indents on my Enve bars that made me nervous. Sent pictures in to tech support and they assured me they were fine.

But yours look like the clamp is putting uneven pressure on the top of your bars, as opposed to the bottom.

Are you keeping the bottom and top stem bolt tightening even?

[drgonzo]

I look at indented bars every time I ride my seven...bought the bars used off my wrench. 3t ergo nova. Had them on for about 5 years now...been through two stems ridden across three states and thousands of miles.

The 3t ergo nova are alloy, correct? I'd be much more willing to push the limits on an alloy bar since I'd expect them to bend before breaking. With carbon, I'm worried about the catastrophic "snap" without warning.

I've sent Fizik a warranty claim, let's see if there customer service is as good as I've heard in other threads ;)

[RoosterCogset]

odd.. is there also a similar shape/indentation on the underside, where the bottom 2 bolts are clamped? Indentation is only from face plate and not the stem's side too, right? It's almost like your faceplate has an undersized curvature.

[drgonzo]

That doesn’t look good to me either. FWIW, I had small indents on my Enve bars that made me nervous. Sent pictures in to tech support and they assured me they were fine.

But yours look like the clamp is putting uneven pressure on the top of your bars, as opposed to the bottom.

Are you keeping the bottom and top stem bolt tightening even?

Yeah it does look that way. Obviously something was awry but I'm obsessive about this sort of stuff. I make sure to tighten by hand, then the classic X pattern with a Park torque wrench, all the while visually making sure all bolts have equal space (i.e. no bolt is flush while the others protrude). Still, far be it from me to say I don't F things up on occasion.

[drgonzo]

odd.. is there also a similar shape/indentation on the underside, where the bottom 2 bolts are clamped? Indentation is only from face plate and not the stem's side too, right? It's almost like your faceplate has an undersized curvature.

Yes there's a similar but not as deep indentation on the bottom as well. Maybe it's the stem plate, it's also a Fizik Cyrano R1.

FWIW, I have a Cyrano 00 bar with Cyrano R1 stem on my other bike and no issues. Both are about the same age and have seen similar miles too.

[Velocipede]

I have one of these. I bought it years ago to inspect frames and components like bars and steerer tubes. It's really nice to have.

https://www.walmart.com/ip/Peroptimist-Endoscope-Camera-Type-C-Borescope-USB-Inspection-Camera-HD-Waterproof-Snake-6-Adjustable-Led-Light-Android-Smartphone-Windows16-4ft/651974836?wmlspartner=wlpa&selectedSellerId=18988&&adid=22222222227299314497&wl0=&wl1=g&wl2=c&wl3=372663531818&wl4=pla-789865970580&wl5=9015339&wl6=&wl7=&wl8=&wl9=pla&wl10=125210027&wl11=online&wl12=651974836&veh=sem&gclid=EAIaIQobChMI0ruTlsWi6gIVyEXVCh3tXgO2EAYYASAB EgKsuvD_BwE

You could have the outer carbon layer compress or indent but inside, there's no sign of damage. Once of these would help see what's up.

[Tickdoc]

That doesn’t look good to me either. FWIW, I had small indents on my Enve bars that made me nervous. Sent pictures in to tech support and they assured me they were fine.

But yours look like the clamp is putting uneven pressure on the top of your bars, as opposed to the bottom.

Are you keeping the bottom and top stem bolt tightening even?

Carbon. Ergo sum? I don’t know, I’m terrible at knowing which naming they use but they are definitely carbon bars and you can see the imprint from the original stem there as well. All bolts are torqued to 3ncm, per extralite spec.

[Duende]

Carbon. Ergo sum? I don’t know, I’m terrible at knowing which naming they use but they are definitely carbon bars and you can see the imprint from the original stem there as well. All bolts are torqued to 3ncm, per extralite spec.

Hey Tickdoc,

I should have been more clear.. I was referring to Drgonzo’s bars not yours.

[RoosterCogset]

Yes there's a similar but not as deep indentation on the bottom as well. Maybe it's the stem plate, it's also a Fizik Cyrano R1.

FWIW, I have a Cyrano 00 bar with Cyrano R1 stem on my other bike and no issues. Both are about the same age and have seen similar miles too.

fwiw i have the R1 stem also.. but FSA bar. no issue though.

[marciero]

I have one of these. I bought it years ago to inspect frames and components like bars and steerer tubes. It's really nice to have.

https://www.walmart.com/ip/Peroptimist-Endoscope-Camera-Type-C-Borescope-USB-Inspection-Camera-HD-Waterproof-Snake-6-Adjustable-Led-Light-Android-Smartphone-Windows16-4ft/651974836?wmlspartner=wlpa&selectedSellerId=18988&&adid=22222222227299314497&wl0=&wl1=g&wl2=c&wl3=372663531818&wl4=pla-789865970580&wl5=9015339&wl6=&wl7=&wl8=&wl9=pla&wl10=125210027&wl11=online&wl12=651974836&veh=sem&gclid=EAIaIQobChMI0ruTlsWi6gIVyEXVCh3tXgO2EAYYASAB EgKsuvD_BwE

You could have the outer carbon layer compress or indent but inside, there's no sign of damage. Once of these would help see what's up.

Scoping the inside could be useful, but important to note that you cant conclude anything from the lack of visible damage. That is, while visible damage on the inside may show the piece is unsafe, lack of visible damage would not prove the piece is safe.

[pasadena]

F-yeah those bars are hosed.
replace immediately unless you want your face to be a swissstop braking surface.

[R3awak3n]

Scoping the inside could be useful, but important to note that you cant conclude anything from the lack of visible damage. That is, while visible damage on the inside may show the piece is unsafe, lack of visible damage would not prove the piece is safe.

exactly.

[glepore]

3t bars among others are notorious for this. Keep in mind that there is almost always thick clear as the final coat on any carbon product, if only for abrasion resistance. The clear is very weak compared to the layup and bruises easily.


Sent from my iPhone using Tapatalk

[weaponsgrade]

That doesn't look good to me either. fwiw, I'm still using my bars without issue.