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I have never had a carbon component on any of my bikes, so I have no idea what sorts of imperfections are perfectly normal minor blemishes that pose no risk. I'm building the bike for a family member and don't want to install anything dangerous.

These photos are from a new fork we just received. It cost almost $300, which isn't high-end by any means, but it is triple what the low-end forks are costing, and it was from an eBay Seller with over 15,000 feedbacks and a 99.9% positive rating, so I figured there would be a basic level of QA that would prevent a defective fork from being sold, and I hope I was right about that.

Are the shallow gouge and the other blemishes on the steerer just above the crown benign?

P.S. I should also add that at 9 o'clock on the steerer, when looking down at the tube from above if you were straddling the front wheel, there is a palpable ridge that runs from the crown up the conical taper. The other side of the tapered section is perfectly smooth. I've added a picture that shows that palpable ridge.

carbon fork steerer imperfection1 carbon fork steerer imperfection2 carbon fork steerer imperfection3 palpable ridge on carbon fork steerer

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  • 5
    That looks bad.
    – gschenk
    Dec 30 '20 at 19:57
  • 1
    I would find an actual brand to buy a fork from instead. Even Chinese brands like Dengfu or Winspace would do. Just not some random guy on the Internet, even if they seem to have good feedback.
    – MaplePanda
    Dec 30 '20 at 20:28
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    @MaplePanda: It is a branded fork, but I did not want to mention the name until I had heard some opinions on those flaws and had also taken the matter up with the Seller.
    – Tim
    Dec 31 '20 at 2:06
  • @Tim That’s fair. Try to find out if it’s a genuine product, because I kind of doubt any reputable manufacturer would let something like that pass QC, even if it’s only cosmetic. Perhaps you’re just dealing with Bob the foreman who sells some of the rejects on eBay when the big boss isn’t watching.
    – MaplePanda
    Dec 31 '20 at 19:46
  • 1
    @MaplePanda: The Seller wants me to pay for the return ($15 USD) and they cannot guarantee a replacement (even though they're still listing the item as available on eBay); they may opt to issue a refund once they have received the return. This policy strikes me as already a tad on the shady side--why not set aside one of the forks they're selling? I hope it's just Bob "Fire, walk with me" and not company policy to treat customers in this manner. I will mention them by name if it turns out that people should be steered away.
    – Tim
    Dec 31 '20 at 20:56
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I don't normally go around inspecting fork steerers, but I suspect that's highly abnormal and a significant cause for concern.

I don't clearly see torn fibers. If you did, that should mean the steerer got gouged in transit. Raoul Luescher is a carbon fiber repairer and consultant with extensive aerospace and bicycle industry experience. He describes some common manufacturing issues with carbon fiber. I think that the gouges might be related to porosity, which stems from improper compaction.

Basically, carbon fiber is a bunch of sheets of little carbon threads. These are immersed in resin, and then the assembly is baked at high temperature and pressure. The carbon plies and the resin are supposed to compact, i.e. come together. If are holes, i.e. porosity, this compromises the structure's strength. (Although normally I would suspect that porosity is inside the structure, not on the surface.) Alternatively, you can have areas that have too much resin, where the resin pooled and perhaps disrupted optimal compaction, or you can have areas with too little resin where some carbon fiber is left exposed. Either of these are bad as well.

Without a background in the subject, I can't be sure what caused these surface imperfections. They definitely look out of the ordinary for a new component.

I suspect you are correct that normal factory quality control would have caught this item and probably destroyed it. In theory, I have heard speculation that some people resell factory second items, like ones that were QC rejected. There are cases where factory seconds with only cosmetic issues get sold. To my knowledge, in the bike industry, these tend to be for accessories. For example, Spurcycle, which makes very high quality and expensive bells has an annual sale on what they call "Frankenbells". These have cosmetic but not functional defects. I haven't seen cosmetic seconds sold as new equipment in official distribution channels. It does seem possible that the rough spots in the steerer might only be cosmetic. However, that steerer is taking a lot of load, and I wouldn't chance it. This isn't a case of paint chips on a used carbon bike.

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  • Thanks for the thoughtful and informative response.
    – Tim
    Dec 30 '20 at 20:01
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    I'd return that one and have it exchanged rather than risking my front teeth and more on this.
    – Carel
    Dec 30 '20 at 20:10
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    Yes it does look like porosity. But I’m not sure how these tubes are manufactured. The surface looks milled, so maybe those layers don’t matter and their only purpose is to be milled away for a precise fit. Doesn’t change the verdict though. Better safe than sorry.
    – Michael
    Dec 31 '20 at 6:33
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The first picture in particular, shows damage that extends far beyond the epoxy resin used to bind the fibers themselves. In pursuit of safety, I highly suggest you return the product if it is under warranty or simply use a different fork.

A fork that fails at the steerer tube is sure to cause an accident that would leave you injured and unable to ride for weeks. Further, now (during the pandemic) is not exactly the best time to get hospitalized.

Stay safe!

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  • 1
    Thanks for the information. Fork is indeed on its way back to the Seller and I'm awaiting a refund.
    – Tim
    Jan 3 '21 at 17:30

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