Dented seatstay on CAAD10 - ride it or not?

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martinko
Posts: 355
Joined: Fri Dec 06, 2013 9:08 am
Location: Slovakia

by martinko

Hello

I had an accident on my 2012 CAAD10 and got injured. But what's also bad is that the bike got injured as well.
I was concerned about the fork to be cracked but it is not. No damage at all, even when the front wheel got snapped.

But then I found small dent on the inner side of left seatstay (see attached photos). I can strip the paint with fingernail. I have done it to check for cracks, but haven't found any, it is just dented.

So Weight Weenies, I want your opinion:
- ride it?
- toss it (well, hang on the wall to be fair, I love this bike)?
- try to sell it?

Thanks.

The frame is otherwise ok with no cracks or any major problems.
Attachments
seatstay 1.jpg
seatstay 2.jpg
seatstay 3.jpg

by Weenie


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ave
Posts: 2134
Joined: Sun Dec 28, 2008 10:15 pm
Location: Hungary

by ave

I know a guy racing with a similar Dent on his top tube. (on a Klein)
I'd ride it.

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TwiggyTN
Posts: 438
Joined: Wed Dec 29, 2010 2:16 am

by TwiggyTN

I'd ride that all day. Just keep an eye on it.

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Qman
Posts: 118
Joined: Wed Oct 23, 2013 9:55 pm

by Qman

Tough call. If I understand you correctly it is on the forward side of the tube, which is a little better than the back side.

Small dents might be ok if the tube is just in tension and the stresses are small. If it has a compressive load then the tube can collapse at the dent.

When you are riding, and particularly going over bumps, that tube is in compression. So, if you hit a big enough bump the tube could suddenly bend at the dent and collapse. I have no idea how big the bump would need to be to cause it to collapse. A Cannondale engineer would have a better idea.

The other load at that location is a forward bending of the tube when you hit the brakes. This puts the dent area in tension, which isn't as bad as if the dent was on the back side. However, over time the tube can develop cracks beside the dent due to the redistribution of stresses around the dent.

You might ride it for years with no problems. Or you might ride it for a while, think it's ok, then have it fail suddenly.

Personally, I'd look into a crash replacement frame so that I'd have the peace of mind to not worry about it while bombing downhill at top speed.

dynaserve
Posts: 269
Joined: Fri Jul 18, 2008 8:25 pm
Location: UK

by dynaserve

That frame will always be worth more to you than anyone else.

topflightpro
Posts: 829
Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

You should be fine to ride it for now, but you do need to keep an eye on it

Aluminum does not like to be dented, and there's a pretty good chance that it will soon crack, at which point the frame is useless. But the nice thing about aluminum is that it tends to fail slowly. So you should see it crack and tear and not fail suddenly.

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kman
Posts: 1117
Joined: Wed Jul 13, 2005 10:51 am
Location: Sydney, Australia

by kman

I'd ride it.
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totoboa
Posts: 88
Joined: Thu Dec 13, 2012 4:24 am
Location: Sierra Foothills, California USA

by totoboa

topflightpro wrote:You should be fine to ride it for now, but you do need to keep an eye on it

Aluminum does not like to be dented, and there's a pretty good chance that it will soon crack, at which point the frame is useless. But the nice thing about aluminum is that it tends to fail slowly. So you should see it crack and tear and not fail suddenly.


That aluminum frame is already a series of welds of torn aluminum. Can't that crack, if it happens, be welded by a qualified TIG operator ? Not saying it's cost effective, but from a mechanical standpoint.

highdraw

by highdraw

Agree with Qman.
Nobody can answer with certainty. That crease in the tube could create a fold point with a hard enough bump or pot hole which could be bad news on a high speed descent. Me?...I may ride it but only short term. I would look into a crash replacement from your local Cannondale dealer.

bfno
Posts: 279
Joined: Sun Apr 13, 2014 2:09 am

by bfno

Lucky you have two seat stays, at least if one does break you still have the other one to support you temporarily
Venge | Shiv TT | Langster | Dogma 60.1 | CruX | Aeroad CF SLX (WIP)

Qman
Posts: 118
Joined: Wed Oct 23, 2013 9:55 pm

by Qman

In answer to totboa's question, no you shouldn't weld a cracked aluminum tube. It's a thin-walled highly stressed tube and putting a weld in the middle of it will only cause more problems.

First, welding it will weaken the metal in the area because it loses its heat treat, and because the weld material is typically weaker than the parent material. The CAAD10 is heat treated after it is welded to increase the strength of the material.
Second, welds work better if there is some overlap between the two pieces. A crack has no overlap so the weld won't be very strong.
Third, adding a weld will cause more distruption in the local stresses and it will just crack again.

Repairing cracks in aluminum is a difficult process. On airplanes they sometimes do a temporary repair by drilling a hole in the ends of the crack and riveting a patch overtop. These don't last very long before the crack starts again. A more permanent solution is to completely cut the crack out and put on a patch. To do this you need to know the stress in the aluminum so that you can make sure the patch and the fasteners are strong enough. Trying to repair a small diameter seat stay would be difficult and not really worth the effort.

racingcondor
Posts: 194
Joined: Fri Aug 27, 2010 4:22 pm

by racingcondor

Qman wrote:Tough call. If I understand you correctly it is on the forward side of the tube, which is a little better than the back side.


My only concern about that is the braking forces on the tube. Better just above the bridge than just below it though I imagine.

I'd be paranoid of the tube folding under heavy braking or riding over a speed bump / pot hole.

Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

I don't think you can responsibly sell it. Whether you would ride it, only you can answer that. The stays are not particularly highly-stressed tubes in that location, but you never know. How 'big' are you? For me, I wouldn't personally ride it and I am 59kg...

The other issue that you seem ok with, but I would be more concerned with, personally, is the fork. I think you suggested that the wheel was broken in the crash. That would suggest to me that there was a fair bit of force applied to the fork, too. The problem with carbon (versus alloy) is that there is often no outward sign of a problem. I had a Colnago Star fork take a hit that bent an Ambrosio Nemesis 32. It is now a Colnago lamp.

martinko
Posts: 355
Joined: Fri Dec 06, 2013 9:08 am
Location: Slovakia

by martinko

Thanks for the tips to all, I plan to visit the shop where I bought it to check it and see what options I have with Cannondale :)

I don't like the idea of riding it more and wait for disaster to happen.

Geoff, I am 72kg (ok, I was, 2 weeks of sitting on the couch don't make me good). I checked the fork, also let my more experienced friend do it and it seems to be ok. No visible crack, no creaking sounds when twisting it, it's straight as it should be, nothing wrong.

Bogan
Posts: 301
Joined: Tue Feb 11, 2014 11:47 pm
Location: Boganville, Australia

by Bogan

What an excuse to get a new bike! Me, I wouldn't ride it, but I have another 20kg on you. That looks like a crease. You will most likely get a stress concentration point in the crease. Not good.
MAMIL? Never. O.F.I.L. yeh! (Old F**ker in Lycra)

by Weenie


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