Bicycle Mechanics - Dent in alu frame

Hi all,

I just bought a Specialized Stumpjumper with a dent in the down tube (cheap). The bike's in really good
nick, hardly a scratch etc. but for this said dent. Now my question to you is: How sensitive to deformities are aluminium frames? I know that they are prone to fatigue and they flex a lot less than CroMo but would dents like these actually harm the frame to the extent that it risks snapping/breaking? I'd be very grateful for any input you might have!

Regards, thomas

If you bought it cheap you got your money's worth. Probably nothing to worrry about to use it as a beater type bike or just tooling around.

Yeah, not worried about not getting my money's worth, with just the fork (fox float80RL) worth almost what I paid for the whole bike :-) My worry is more in the 'frame cracks in action and I injure myself fatally' department. I don't really get out on the trails much so it wouldn't take much abuse. Mostly commuting, at the moment at least (a bit difficult to get out of London...).

Replacing the frame wouldn't be a major prob apart from the financial shock as I've built a bike before (got stolen in January), but I'd be happy if there wasn't any need...

thomas

Looks pretty ugly, but consider:

1. Generally, when a frame cracks, you still have two other members in the frame holding it together, so you don't go down.

2. The down tube is not loaded in compression, so dents won't make it buckle anyway.

I wouldn't worry about a dent in the downtube, but I'd worry about how the bike got that dent in the first place : if something heavy hit it in the garage or something, probably no problem, but if the bike got into an accident, you might want to check that the frame is still straight.

Hi,

Excuse a stupid question but how can you check that it really is straight? I guess take it to a LBS
would work, but If it would have been in an accident wouldn't there be more visible damage like scratching and stuff? The whole bike's in mint condidtion, not a scratch anywhere, apart from the offending dent. And I've been out on the bike a few times and it feels absolutely fine; not percepitively
off center in any way...

Here are two more pics:

Hi, Excuse a stupid question but how can you check that it really is straight?

Well, carefully eyeballing the frame would reveal problems. You can also put the two wheels on without tires, sandwich the two rims between two square-section tubes and see if the wheels are aligned. Of course, for a thorough check you'd need a jig, but you can see a lot with your naked eye. If it looks fine and rides fine though, it's probably fine :)


but If it would have been in an accident wouldn't there be more visible damage like scratching and stuff?

You never know. I crashed hard on my mountain bike once, it landed on the curb (I guess, I was busy taking a tumble while the bike was sliding to a stop) and the only visible damage was a big scratch near the bottom bracket. What I meant was, something quite unusual happened to your bike that dented the frame, and since you don't know what, it might not be a bad idea to check if the frame has hidden damage as well.

Try riding it without hands. If it pulls to one side, it may be out of alignment. If it runs straight, you're probably fine.

Right, have been cycling around on it quite a bit the last days and the frame seems absolutely fine. Will take out an insurance though so perhaps I can claim it on that...:D

Cheers everyone for the input!