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I wanted to lower the stem on my one month old road bike and noticed that the stem already left a noticable mark in the carbon steerer. Seems that the lower edge scraped into the material. Stem was always properly tightened and headset adjusted. I know that carbon is a much debated topic with a lot of panic and confusion but this scratch leaves me with a bad feeling as I would prefer to keep my face and teeth as long as possible.

Anyone know if this kind of damage is in the "to be expected" range? As a side question: When reattaching the stem I made a small scratch on the upper end of the steerer because the stem got jammed. Nothing compared to the big circular scratch, but would be glad if someone could tell me if that's ok (last two pictures).

1 2 3 3.1 4 5

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    Can you carefully run your finger over the inside of the stem where it mounts on the steer tube and see if there are any sharp corners or rough spots that could cause those scratches? And I do mean carefully - if there is anything sharp there, it could be sharp enough to give you a decent cut. Jun 19, 2023 at 13:56
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    I tried to check for that but couldn't really feel a sharp edge. Definitely nothing so sharp you'd risk to cut your finger. Maybe a tiny edge but nothing more. But there are visible marks where the black paint/anodization has rubbed off a little (added another picture). Regarding my warranty possibilities for now I avoided to give the stem inside a sandpaper rub.
    – conste
    Jun 19, 2023 at 14:09
  • Particularly in the first photo, looks like the scoring goes right around the steerer tube. That to me would mean that there is something in there rotating that maybe shouldn't. Assuming the stem is tight, then perhaps the issue is the top edge of the spacer, or perhaps some grit has got in between the spacer and stem
    – Hursey
    Jun 19, 2023 at 20:35
  • I think it actually results from the stem as the scoring has a gap on the back where the stem clamps/bolts are clamping. But indeed it is weird that the marks are so regular and all around. I only needed to tighten the bolts a few times (of course with a torque wrench) because I was fiddling with the headset but didn't move/rotated the stem for that. I only had to rotate it once when I received the bike in mail and had to do the initial setup. So it actually has to result from riding the bike.
    – conste
    Jun 19, 2023 at 22:03
  • @AndrewHenle It is good practice to use a cotton ball or something similarly fibrous when checking for sharp edges--not worth cutting yourself by accident.
    – MaplePanda
    Jun 19, 2023 at 22:47

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I would recommend getting this warrantied (specifically, get the fork and stem replaced). Although the groove is not terrible (i.e. the bike is not immediately an unrideable safety hazard), objectively speaking, it is damage that should not be there. This is a clear case of defective product sold as new, and you should have legal protection via your jurisdiction's lemon laws provided they exist.

As seen in your fourth photo, the lower edge of the stem appears to have a raised edge, which cut into the steerer to cause the damage. The gap in the stem corresponds with an interruption in the groove, and even the amount of shiny metal exposed on the stem (indicating the severity of the raised edge at that point) corresponds with the changing depth of the groove. This should not be the case; as matter of fact, well-made stems will often have a chamfer on both ends of the clamping surfaces to specifically prevent this from occurring (as well as offering a smoother transition to reduce stress concentrations). See an example below (RaceFace Turbine R).

Don't worry about the scuffs on the upper part of the steerer. No need for concern whatsoever there.

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