Small dents on bicycle frame

Question

Two weeks ago I bought Trek Checkpoint ALR5. Bike rides pretty well. It has aluminium frame. I bought it primarily for bike packing trips as it has ton of mounting points.

After riding it for 2 weeks and hitting some easy gravel roads I found two relatively small dents on bicycle's frame. They are probably caused by flying rocks from the wheels. In total I rode around 100 km on gravel trails and the riding wasn't too extreme. Those dents made me a little bit paranoid about the bike's frame strength, and made me wonder how the frame will look like after one year.

Are these dents normal or do they show that bicycle has a fragile frame? Can they cause problems? Do they compromise the bike's structural strength?

Pictures of the dented area:

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Here's a video:

Answer 1

If this were an ultralight aluminum frame, then even those dents would be potentially concerning. But the Checkpoint is not such a bike. Ultralight aluminum isn't even that common these days. Yes, aluminum theoretically has a finite fatigue life, and those dents will presumably reduce it. However, chances are that Trek anticipated that this type of frame would occasionally take hits and they probably selected wall thicknesses appropriate for the use case. Hence, I agree with Criggie. Also, those dents look very shallow.

You peeled back a plastic frame protector. It looks relatively thin. I assume it was to protect against damage from abrasions. Effetto Mariposa's shelter tape (I have this on my gravel bike) is 1.2mm thick and does offer protection against light impacts, as demonstrated in this video by Cantitoe Road, a shop. I have to imagine that other manufacturers make similar tape. This PinkBike review covered a few brands of frame tape that are all less than 0.5mm thick and are designed to be proof against abrasions but not impacts. Also note that even something like the Effetto Mariposa tape won't protect against a big impact. Nevertheless, you could consider this.

Answer 2

Looks like you've peeled back some paint protector to see the dents better. Was there damage to the plastic from rocks?

Also, these dents seem to be too high up the downtube to have come from stones flicked off the tyre. I'd expect anything like that to be concentrated around the BB shell and the very bottom of the downtube.

My suspicion is they are caused by bad handling at some point, or possibly by over-zealous clamping in a work stand.

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Are they a danger? Probably not - but the first damage on a nice new shiny bike is always disappointing.

Now you've noticed, make sure to check this area whenever you do maintenance. As long as they don't change, get deeper, or start to crease/crinkle or crack then you'll probably be fine to put another 100,000 km on this bike.

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If you want to repair it, then consider aluminium does not unbend in the same way steel can. So trying to pop the dent out of aluminium will make the frame weaker than it is right now.

For a cosmetic fix, you could clear the paint from the dents, sand and fill it with automotive bondo, then sand, and repaint. However that stops you directly observing the dent in the future. Plus matching paint is hard to do.

And, if the dents are from your riding to date, you'd expect more similar dents by the end of another similar ride. So after 1000 km your downtube should look like the moon's craters if the dents are from riding.