Pulsify

I'm still relatively new to cycling. I recently switch my stock 100mm Canyon (Endruace AL) stem on to a 110mm FSA stem. Then a few months later, swapped that 110mm FSA stem to a 120mm FSA stem. Upon removal of the 110mm stem, I noticed the stem left behind two very small lines vertically along the carbon steerer where the stem clamps. The lines can be lightly felt when brushing my fingers over them. They are NOT dents OR cracks, I promise; if anything, it feels like braille protruding ever so slightly outwards like a mountain ridge --- maybe like a super, super thin layer of carbon folding over itself? Again, it would be hardly noticeable to the vast majority of people and I'm 99% sure this is fine, but I am OCD about safety and wanted to double check. For reference, I never went over 5nM with my beam torque wrench as I know over-tightening is a real problem. (sorry about phone picture quality).





EDIT: oh boy, this video looks similar to my steerer. Maybe it's delaminated?

Crankycrank

I always preface questions about photos of CF damage by saying I can't guarantee any opinion as photos don't give all the info you need. Having said that, it looks fairly normal but take it to a shop for a professional, in-the-flesh opinion.

blamester

Seriously you felt two tiny lines on a carbon steerer and you want reassurance.
Look at it and use your head. Think about it.
Install the handlebars.
Do they fell o.k
Do they look o.k.
You have already been riding this bike with those marks there and you didn't know.
Nothing is perfect.

2old

We know carbon fiber is notch-sensitive, and the ramifications of a break in that area will be severe. However, you say it isn't "scratchy" and, as noted above, have been riding with the system, so probably OK. That said, possibly some type of compression marks, so you might call an expert like Craig Calafee for advice.

woodcraft

I don't think there is a "normal manufacturing line",

so that's likely from the first stem being put on.

I suggest hitting it with a bit of 320 wet/dry sandpaper to get rid of the marks-

then they won't be there to worry about.

UKFan4Sure

A little harsh, don't you think? He's not an expert on CF, so he asked. I say, the only dumb question is the one you don't ask. Give the guy a break.
How the bars "look and "fell" (sic) have nothing to do with it since CF breaks catastrophically and quickly at times. A lot of people have ended up in the hospital by CF components that had issues and didn't know, even professional riders.

02Giant 

Either I am living on the edge or just stupid. I would ride it without question.

They look like they match the width of the gap in the stem.

blamester

Ok. a bit harsh. But maybe he had a think about it. If you are going to do your own mech work then you are going to have to use common sense.
Look and feel do matter. How did the installation go? Did it feel ok?
Is the stem properly square?
Does it operate normally?
Is it the same as before?
I asked him to think about what he did and draw a conclusion. Is it ok or not?
And if you can't decide you can't ride it
And no amount of opinions on here can change that.
I will try to be kinder in future and a little clearer about what I mean.
But no one is perfect.
​

HillRider

One other consideration, they are vertical (longitudinal) lines. If they were circumferential, i.e. horizontally around the steerer, they could act as stress raisers and contribute to possible failure. As is, they could only contribute to vertical cracks and that is very unlikely.

UKFan4Sure

I've asked Mr. Luescher to weigh in on the situation. Maybe he can advise..

UKFan4Sure

Here was his reply:

"It could be a surface mark or go deeper, I would need to scan it."

blamester

Well that's cleared that up.

UKFan4Sure

Yeah, well that's the thing with carbon. No one wants to put their ass on the line.

2old

As noted above, the material fails catastrophically in which case I err on the side of caution. Most carbon fiber is clear coated; if you can see the coating and it hasn't been penetrated, probably OK. I has a very slight mark/scratch on carbon MTB bars, which didn't penetrate the coating and used them for almost 10 years.