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Big dent on steel frame

Old 08-05-21, 05:14 AM
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Foxtrot Bravo
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Big dent on steel frame

While I was bikepacking the other day, I took a big fall. When I inspected my bike at camp that night, I noticed a biggish dent on the chainstay of my steel Kona Sutra.

The dent is visible from the side and about the size of a quarter and about 5 millimeters in. It doesn't look like the chainstay shape was deformed as it happened in the largest part of the tube. There is no apparent crack either. I would love to post a picture but I'm new to this forum so I'm not allowed.

Is it just a flesh wound? Should I have it repaired? Can it be repaired?

Thanks!
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Old 08-05-21, 05:20 AM
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Chainstays get dimpled all the time for tire/chain ring clearance. Just Say'n
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Old 08-05-21, 06:31 AM
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I'd be happy to be corrected and to learn something, but when I think of the chainstay, it's mostly in tension. A dimple in a tube under tension doesn't scare me as much as a dimple in something in compression (e.g. the seat stay or to some extent, the top tube). A dimple in a tube does significantly lower buckling strength in compressive failure as the dimple is an easy starting point for the failure.

Picture?
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Old 08-05-21, 06:59 AM
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Originally Posted by WizardOfBoz View Post
...happy to be corrected and to learn something...
It has been forever since I looked at this but I believe the right stay sees the highest loading and is in compression in all situations other than braking and the left stay is lightly loaded in tension.
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Old 08-05-21, 07:16 AM
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Originally Posted by WizardOfBoz View Post
Picture?
I think because of the forum rules, I'll have to reply 8 more times before being able to post one so... Suspense!

The tube is already not tubular (round) in shape, so I think it is inherently more fragile. Also, contrary to the dimples made on chainstays to allow larger tires, this one is on the outside of the tube...

Thanks again!
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Old 08-05-21, 07:32 AM
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Originally Posted by Foxtrot Bravo View Post
...contrary to the dimples made on chainstays to allow larger tires, this one is on the outside of the tube...
Pic Assist - https://www.bikeforums.net/g/picture/22108594


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Old 08-05-21, 08:19 AM
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Wow thanks cb400bill !
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Old 08-05-21, 08:54 AM
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I can't make it out well enough in the pics to say anything much specifically.

However in a steel tube bike, I generally wouldn't worry too much or too long. If everything is working correctly and in alignment, then just keep an eye on it for the beginning of a fracture. If you clean your bike regularly, that'll probably be often enough to check it.

Though steel can in some instances suddenly fail completely, steel usually will show evidence of impending failure long before it happens. And even when it does, it usually will just slowly bend before the fracture completely severs the tube. ...IMO!
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Old 08-05-21, 10:48 AM
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That looks to be a significant dent. No guarantees, but just looking at the pictures, it looks to be ok for riding. I would maybe limit it to trails that are not going to put the maximum stress on it, and keep observing that area. A tongue in cheek, friendly suggestion. clean all the gunk off the bike and you might save a few pounds and put less stress on the chain stay.
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Old 08-05-21, 08:19 PM
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Originally Posted by easyupbug View Post
It has been forever since I looked at this but I believe the right stay sees the highest loading and is in compression in all situations other than braking and the left stay is lightly loaded in tension.
Good heavens, I believe that you're correct. If F is the thrust your wheel generates forward, then the force on the freewheel from the chain is F*R/r where R is the wheel radius, and r is the radius of the rear sprocket in use. Because they both push the wheel forward on the frame, they add so the total forward force on the wheel is F*(1+R/r). Most of that force will be on the side closest to the chain and must be counteracted by the chain stay.

For some reason I was just thinking of a bike gliding along without chain forces. To quote my pal, Homer, d'oh.

Thanks for pointing my error out.
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Old 08-05-21, 09:31 PM
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That's you NDS chain stay which we now agree is in tension, however bending stress are far higher and I still would not worry following the precautionary good input from above.
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Old 08-05-21, 11:46 PM
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Maybe it's OK, maybe not. But it is weaker.
That's a perfect place for a CF wrap fix. I have done a bunch of stuff with CF, both separate and wet layed right on the frame.
I just put it on top the paint or powder coat, that has zero chance of coming loose anyway.
So if you do this, I would straighten the stay first. Then put a 4" or 5" band on, 3 layers. You can get little kits for $50 maybe.
Fill the dent with anything.

Last edited by GamblerGORD53; 08-05-21 at 11:50 PM.
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