So there is a local bike for sale...Fuji Cross bike. Has what looks like a substantial dent in the top tube. Now, past posts on the safety of dented aluminum say yes, no, or maybe. Anyhow, this looks pretty substantial. Of course the seller says it doesn't affect the structural integrity which is ridiculous. Of course it does. The question is how much. Opinions?

If it was steel I would say its fine to ride. Aluminum, I dont know. That being said I would value the bike for its components only. Frame has no value.

Do not buy it, my opinion.

Is it safe? No. Is it dangerous? Also no, unless you are 240lb and thrash the bike regularly.

For normal rides, you won't encounter any problems.

Should you buy it? For anything other than parking lot speed cruising, no .

I honestly don’t see that top tube crumpling under any normal use. In any event, it’s not like it’s not right in front of you if, by some remote chance, it started to go. The top tube is under compression, so if it goes as a result of this dent, it’ll bend and crumple, and I don’t see this happening catastrophically, but rather a slow bending over time. Would this bike be my pride and joy? No. Would I ride it? Absolutely

it hard to tell from these pictures, any idea how large the tubes are and how deep that dent is?

guess you could have saved yourself a post, you got the same kind of answers you knew were coming.

I've heard stories of people riding bikes with dents more significant than that in the top tube for years.

Would I ride it myself? Sure. Gently. If the price is right. And the frames a good fit. That dent just isn't in a high stress area of the frame.

I know that's true. Sigh.

I’d pass unless the components are compelling enough to use on another frame and of course it is cheap enough.

If there is an aluminum welding specialist near you, I would go for it.

I could understand feeling stuck with a frame you had dented yourself and talking yourself into keeping it. Your costs are sunk, it’s embarrassing, you don’t want to afford another, it might be ok...

But buying one?

what would you be welding to fix a divot like this?

I'd pass. Even though all my riding is relatively tame I'd still not feel comfortable riding this.

Why waste your money unless the bike is priced cheap as a parts donor? Otherwise there are better ways to spend your money. To my mind, the OP's question is as much about economics as it is about the dent.

I think others have summed up that the value should be based on the components. Wheel quality and condition is something I’d take a good look at because they “can” represent a significant cost.

One aspect about these types of questions is to step back and ask yourself, “Do I even want a a Fuji cross bike?” It is easy to get caught up more in the good deal and less in the actual item. It is somewhat humorous to read a suggestion of buying a dented cross bike and then riding it gently.

John

You need a paintless dent repair shop, like the car insurance companies use after hail storms.

No that bike is not safe. Once aluminum gets dented like that is creates stress risers and can crack. It may not crack right away, it may never crack but that is nothing you can predict. Honestly it isn't worth it unless the parts are spectacular and the price is low enough to just be buying parts.

If that bike has that damage what caused it? You will never know and the owner may or may not tell you the full story, most people probably wouldn't give up that information to someone buying their stuff. When people bring us bikes at the shop that have damage or serious issues, it is usually the same thing "Just Riding Along" as if it magically happened. I get it, some of these incidents could be quite embarrassing or cause other issues. If I did the damage to the bike I could then take the risks knowing what happened but someone else's bike no way.

Let Drippy buy it, he is really an expert in all of this. However you should just stay away unless buying for parts and the parts are in good condition and for a good price.

I'd buy it and do a carbon fiber wrap repair. Some early "carbon" frames, such as Raleigh's top Technium mountain bike frame, used aluminum frame tubes wrapped with carbon fiber. Should be easy to do and comparatively inexpensive, and the top tube will be stronger than before the damage occurred.

As noted earlier, dented aluminum will eventually crack, and then tear. Once it cracks, it's worthless, and no one can repair aluminum frames yet. As for it being dangerous, no, it is not dangerous. Unlike carbon, aluminum cracks and tears slowly. It won't suddenly crack and fall apart. The crack will start small and grow, so you there is no danger in riding that frame for now. But as said, you don't know when it will crack. It may crack tomorrow, it may never crack. I had a dent like that on a frame and it cracked the next ride.

As for the cause of the dent, I'd guess that the bike crashed and the bars slammed in to the top tube. That's how I dented mine.

If it's cheap and the rest of the parts are worth it, then get it and ride it as long as you can. Just know that at some point, you will likely have to replace the frame. If you're not up from swapping parts over, then pass on this one.

The Dripster knows all...

Nothing. It's a nonsense comment.

Not to fix, but to strengthen the area. Would take it down a hill and 45 MPH, probably not, but for just tooling around, no issue.

You'd just fill in the divot with weld and sand it all smooth. Would work fine with steel (although you'd probably fill it in with bronze). But Al used on bike frames usually requires post welding heat treatments involving baking the whole frame in an oven which rather puts the kybosh on the whole thing.

Not having tried it, but maybe expanding structural foam could be of use.

It is up to you to figure out the math for the intended use.
Of course the Risks vrs Rewards are going to be something to think about before going forward.
Possible Pros: Pushes the dent out, increases strength, & aids in prevention of future dents in the local area.
Cons to consider: Cracks the frame, creates a new noise to tolerate, harbors moisture & dirt, provides humor for the interwebs folks.