I have found this used Specialized Diverge(aluminium frame) and am wondering how bad this scratch/dent on the side of the top-tube close to the seatpost is. I have looked at other posts and I don't think it is dangerous now, but how big is the risk that it will get worse?
7It doesn’t look bad, but it’s always hard to judge, especially with the paint still on. It would also be interesting how this dent happened. Did the bike simply fall over and hit something or was it a full blown crash at high speed which possibly damaged other areas?– MichaelDec 18, 2022 at 9:17
1Or is it an abrasion of some sort?– Daniel R HicksDec 18, 2022 at 14:34
1Side question: Does aluminum fail catastrophically, or will cracking paint provide sufficient warning?– Ray ButterworthDec 18, 2022 at 15:03
Very hard to tell in a photo - but it looks more like a scrape from leaning the bike on something, and it rolled. Then a PO painted over it without sanding the edges to blend ? This might not even be a dent, it could be paint.– Criggie ♦Dec 18, 2022 at 18:14
1Is it a risk, probably some risk there. Is it a risk that will get worse, possibly some risk. Is it enough of a risk to be of concern, that's up to you. Looks almost cosmetic to me, but to my eye (all be it from a photo), there does look to be a very slight discolouration (could be lighting) there so it might have had a touch-up to hide some damage– HurseyDec 18, 2022 at 20:23
Not bad. Fortunately it is small and not in a reinforced area.
It can be hard to judge damage from a photo, as it is in 2D and you can't control the lighting or the viewing distance. There doesn't look to be much depth to the dent, assuming it's not just paint.
In other contexts, you might want to look for cracking around the dented area. Even little fractures in the metal surface would not be a good sign, but you have to distinguish cracks in the metal from cracks just in the paint. Here is one example where the viewer consensus is that any apparent cracks are likely to be paint deep only. The dent in that post is quite considerable compared to what I think I see in this question. That is, aluminum frames can be rideable after a fairly significant dent. Here is a different example where the consensus is that this is no longer rideable.
Another thing you might consider is to search Stack Exchange for examples of dented aluminum.