"Dent" in seat tube to accommodate front derailleur?

While meticulously cleaning my aluminum frame the other day, I noticed a sizable "dent" behind the derailleur. There weren't any scratches to indicate that it had suffered any maltreatment and it was in a very inaccessible place. Admittedly, I panicked at first!

I am quite surprised it had gone unnoticed for a full 2 years. In the weird lighting, it looked as if the indentation might be uneven but upon closer inspection, it turns out it is quite a uniform, flat surface.

Is this sort of frame modification common practice? Does it compromise the integrity of the frame? :p

No, it is not a practice I have ever heard of to dent a tube to accommodate a front derailleur clamp. More likely is that someone overtightened your front derailleur clamp, creating the dent (as aluminum is quite soft that way).

Another possibility, if your chainstays are very short and the tire is very close to touching the seat tube, that the flat surface was intentionally created to allow for tire clearance. A picture would help tell the story.

Assuming it is some kind of damage it is probably fine structurally, but if you want to be sure, you will probably have to remove the paint around the dent and look for cracks. The problem with aluminum is that a crack can spread and cause tube failure pretty fast.

I'd recommend not worrying about, but keeping an eye on it. If you see a crack developing, stop riding it and have the shop where you bought it assess it.

I'd check out bikes just like yours, too, if you can to see if they have it. What kind of bike is it?

Karen

yes, frame makers put that dent in there. Some are more artful than others. And if they do it right it doesn't affect the integrity!

It does look machined which makes me feel (somewhat) better.... Thank you for your comforting words :)

I will definitely be browsing the other aluminum bikes for this feature when I go into the shop :)

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Originally Posted by Ana

It does look machined which makes me feel (somewhat) better.... Thank you for your comforting words :)

I will definitely be browsing the other aluminum bikes for this feature when I go into the shop :)

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Great photo, I know exactly what you're referring to. Yes, the dent formed at the factory for front derailleur clearance. (It's not needed in every case, but likely with certain derailleurs and say triple cranks for example).

I just browsed the Trek bikes while I was getting my seatpost cut and most of the aluminum frames have the same indentation mine does :)

Yay. I'm so glad my frame isn't structurally compromised :)

something new I learned today. Great photo BTW. :) Thank you for sharing the information.

See its a triple 105. the chain looks so clean. not black like mine.:confused:

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Originally Posted by smilingcat

See its a triple 105. the chain looks so clean. not black like mine.:confused:

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Why thank you! I am rather meticulous about my chains...and riding in fair weather ;)

I was just noticing the grime near my derailleur.... ;)