Bicycle Mechanics - Dent in aluminum top tube.

As you can see from the attached pictured there's a dent in the top tube of my aluminum Fuji Pro bike. The dent is circled with a red oval and there's a penny there to give perspective. The dent is about as long as the oval but not as wide. I searched for this problem on bikeforums.net and there are mixed responses but it's hard to gauge anything because all the pictures have been deleted so I can't see the dents that are referred to.

I ride on so-so roads but always in heavily trafficked areas so I'm worried about the frame cracking right when I'm in the middle of traffic. Any advice would be greatly appreciated. Thanks.

Doesn't look too serious to me. If there's no tearing of the metal and you can sit on the top tube and put your full weight on it without making it worse then it's probably OK. Watch it closely but dents happen and normal bike riding is unlikely to make this one any bigger.

Be prepared for a lot of bs about aluminum's fatigue strength in this thread.

It looks like you dropped something on it - true?

Actually the bike fell while it was in my room. I don't remember very well but it must have hit the corner or edge of some hard object. Anyway, that's when I realized how thin the aluminum walls are. If it had been one of my steel-frame bikes I don't think the same would have even caused a scratch.

Aluminum doesn't tolerate this sort of thing nearly as well as steel. The problem part is of course inside the tube. It is likely to have shortened the life of the frame, and certainly killed what little value it had before (bikes lose value like mobile homes). I think the risk of riding is very low and that of catastrophic failure very low, but if the frame is going to crack this would be one place for it to start. Generally speaking I would not sweat it much. (I have had a steel frame crack in half while riding, was about 15miles out when a previously cracked and welded 531 down tube broke near the downtube shifter clamp.
I found a piece of electrical wire and wrapped it around the downtube shifter clamp and the top tube and rode home. Kind of bouncy but got home. Frame was definitely squirly before the crack propagated all the way around.)

I had a similar problem with a steel frame. Luckily one of my friends is a metal engineer and this is what he told me. "I would not ride it" I trust him very much and his expert opinion has proved to be the truth in the past. Especialy if that is double butted. Think of it like it's a soda can with out imperections my mother inlaw can stand on it and the can will support her weight. Yet with any wrinkle or dent it will collapse under nominal stress. With that said do as you wish it might last 5 more years but it might last 5 more miles. Ride safe Happy New Year

Just watch for cracks. I would sand down the area around it so you can see what's going on clearly.

Think of it like it's a soda can with out imperections my mother inlaw can stand on it and the can will support her weight. Yet with any wrinkle or dent it will collapse under nominal stress. With that said do as you wish it might last 5 more years but it might last 5 more miles. Ride safe Happy New Year


++++

Wouldn't emerging cracks be easier to see in the paintwork that in scuffed up and subsequently coroded aluminium?

Richard

++++ Well... get your mother-in-law to stand on a soda can with the same wall thickness and tube diameter as the one on the bicycle and with a similar dent, and see how far it spears into her foot. Assuming the mother-in-law is pretty hefty, I doubt that her weight even then would come anywhere near the forces transmitted by the headtube to the top tube, except in a head-on crash (which then would make any dent in the top tube moot anyway).

It also gives lie to the longevity of indentations and bends in alloy tubing most likely also on the bike in the fork and chainstays (and probably the seatstays).

Sorry, but the mother-in-law analogy does seem to stretch the rubber band a bit far.

Of course, if the top tube is as thin as a pop can, riding it wouldn't be advisable. But assuming it is a normal aluminium frame, riding it shouldn't be a particular problem. The dent does not appear to have caused a misalignment of the entire frame because of the localised impact.

Regular checks to see if cracking has extended out from the dent would be a good idea (but then regular checks of any frame is a good idea to check for cracking, anyway). Unlike a fork, too, a failure in the toptube is likely to be more progressive that sudden, and you would expect a degree of noodliness to occur before final fracturing.

I don't see how much of anything can be ascertained from that particular photo; it's too small, not clear enough, in poor light, and doesn't even show exactly where on the top tube the dent is. I hope the dent doesn't cause problems for the OP, but there's no way a meaningful assessment can be made from that photo-

Wouldn't emerging cracks be easier to see in the paintwork that in scuffed up and subsequently coroded aluminium?

Richard

Aluminum doesn't corrode that much, and when it does it's pretty easy to polish it up.

I had a similar problem with a steel frame. Luckily one of my friends is a metal engineer and this is what he told me. "I would not ride it" I trust him very much and his expert opinion has proved to be the truth in the past. Especialy if that is double butted. Think of it like it's a soda can with out imperections my mother inlaw can stand on it and the can will support her weight. Yet with any wrinkle or dent it will collapse under nominal stress. With that said do as you wish it might last 5 more years but it might last 5 more miles. Ride safe Happy New Year

I can't believe. One small dent on a steel frame and you have to chuck it? I have a double butted steel frame commuter that sustained a dent on the top tube last around ten years ago. The dent is around half an inch long and around 1/8 of an inch deep and was really unsightly at first but I got used to it. This bike has been used regularly since without any issues at all. I think the soda can analogy isn't quite applicable here.

You don't worry so much about the dent per se as whether that's going to lead to crack formation, and if so, how fast the cracks propagate. That is, how much warning do you get, etc. With steel, you get more warning than you do with aluminum.

I can't believe. One small dent on a steel frame and you have to chuck it? I have a double butted steel frame commuter that sustained a dent on the top tube last around ten years ago. The dent is around half an inch long and around 1/8 of an inch deep and was really unsightly at first but I got used to it. This bike has been used regularly since without any issues at all. I think the soda can analogy isn't quite applicable here.

he said its an alumn frame. but I agree with well biked, you really can't tell much from the photo. did it change the geometry of the frame any? alumn. tubes are not as thin as soda cans, in fact, some of the ultra light steel frames are thinner than alumn. today. an impact might dent alumn. but it is still pretty strong stuff. I have an alumn. cross bike that took a hit to the down tube. small dent but no effect on the bike in any way. I would keep an eye on it.