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I bought a new aluminium folding bike frame last week, and this weekend while I was cleaning the bike, I noticed this very tiny dent on the top tube of my frame. It was barely noticeable and I didn't notice this until I noticed the light shining weirdly on this part of the frame. Running my fingers along the frame, I noticed there is this tiny indent. enter image description here

I can't figure out what could have caused that tiny dent/ indent (maybe an allen key dropped or something while I was fixing up the bike?), and I'm not sure whether this was like this from the factory.

What I am concerned about is whether this will impact the structural integrity of the frame? I am guessing not but would like to hear from you guys as well. I know on larger dents the advice is generally not to take the risk.

Or is this just a byproduct of the manufacturing process?

Any opinions would be greatly appreciated!

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  • Is it a race bike? a mtb? a commuting bike? from the picture it is not clear.
    – EarlGrey
    Sep 27, 2021 at 7:10
  • It is a 20" folding bike. It looks like this: cyclicworkz.com/bicycle/fnhon-tornado
    – trenz
    Sep 27, 2021 at 8:02
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    If the depth is less than the thickness of the paint, it could be a result of solvent boils/popping during the painting process - if the top of the defect was sanded off then a dip would be left in the paint. If you happen to know someone who paints cars, I expect that they would immediately be able to tell you if that was the case. Sep 27, 2021 at 15:54

3 Answers 3

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That is your bike's first "war wound" and should not compromise the integrity at all. It is disappointing to have a new-thing and is now no-longer showroom clean, but that's life - keep enjoying your bike.

Any bike that gets used will acquire chips and scratches, scuffs and memories over time. The bike grows character as these accumulate.

Just keep an eye on it when you do your periodic maintenance, and if it ever changes then stop and reevaluate.

If it really bugs you, put a sticker on it.

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    Note for others with different frames: This answer is true for any metal frame. Even aluminum can take such slight local deformations without loosing significant strength. But for a carbon frame, even the tiniest dents require examination of the materials structural integrity (i.e. are they just in the paint, or did the material crack?). Sep 27, 2021 at 12:46
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Location is close to where tensile stress are strongest (i.e. where the frame must be strong), but I would not worry about such a small dent unless it is a competition frame (i.e. it may be very light because material usage have een optimized ... and therefore any excess stress will shorten the frame life).

Luckily for you, that is a perfect dent: its location is very convenient to monitor it, your subconscious will notice if suddenly it starts growing or if it changes colour (all possible signs of a crack growing underneath the paint).

Enjoy the ride!

Ps: Reg worst-case scenario, i.e. bike theft, now you have a personal tag to identify your bike, but do not forget to save the serial number somewhere ...

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    I’m not sure what kind of riding is making OP’s top tube see tensile forces. Usually the DT and CS are tension, TT and SS are compression. Excellent answer otherwise though!
    – MaplePanda
    Sep 27, 2021 at 7:40
  • @MaplePanda its not clear in the photo but I think this is a "one-tube" folding bike, so its the top tube and down tube in one. Top edge of this main tube would be tensed in braking, and compressed under normal riding, and under shear force while pedaling hard out of the saddle.
    – Criggie
    Sep 27, 2021 at 7:58
  • Thank you! My frame actually does not have a downtube as it's a folding bike (the model is Fnhon Tornado, similar to a Tern Verge), so I'm not sure how the analysis changes? I also tried chipping off the paint at that area (ok, why did I do that?!) to see what's going on underneath and now I'm not even sure if it's a dent or a paint defect... Up close with a magnifying glass I can't tell if there's a dent or not, it's just that when I run my finger across, it feels like there is a minute indentation, but then again it's hard to tell as that area of the frame is a curve..
    – trenz
    Sep 27, 2021 at 8:01
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    @MaplePanda I agree in general (compression is relevant, fatigue is by cycling compressive stress-no stress), but the dangerous event that will pop open your frame is a tensile stress peak load (such as a bump, or sudden braking). The reason we build bike with steel/alu/carbon is their high tensile strength, for compressive loads alone we would be fine with bicycle made of granite :) . OP: even if your bike is a foldable with a single tube, I still stand by my answer. You will have to worry about the hinge mechanism, before you need to worry about the (dented) frame ...
    – EarlGrey
    Sep 27, 2021 at 8:08
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    Thank you all for the reassurances. Now I just need to deal with the fact that my bike is no longer "perfect" -- then again, what is?
    – trenz
    Sep 27, 2021 at 8:35
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Thanks guys. I scraped off the paint to the raw aluminium out of curiosity. Still not sure if it is a dent or just an optical illusion. From certain angles/ lighting, it looks like there is a slight depression; from other angles/ lighting, it looks completely flat. Running across the portion with a sharp pick to "feel" for any indentation also proved inconclusive.

Anyhow, what was more concerning was that I think I might have scratched a little of the raw aluminium off(!). I proceeded to file that area and covered it with black nail polish.

Based on all the replies provided so far, I figure that the structural integrity of my frame remains uncompromised. I'll probably put some 3M clear protective tape to seal in the nail polish and perhaps call it a day :)

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    ok, now it really stopped being a new bike and it became your bike :)
    – EarlGrey
    Sep 28, 2021 at 6:49
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    Caution: This activity may void your warranty
    – FreeMan
    Sep 28, 2021 at 17:55

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