odie91

ok, so i noticed there are ZERO people viewing the framebuilders forum, so for the cross-post...

how thick is the tubing of an aluminum frame, specifically the chainstay tube? i scraped it hard on a curb, and it scratched a pretty thick chunk out of the tube. no dent, but a deep gash. should i be worried? it's a Specialized road frame built in 2004, in case that info helps (Specialized Langster to be exact). i'm not sure exactly how deep, but i'll try to measure it when i get a chance.

HillRider

There is no specific thickness as frame builders use thick wall tubes of a weaker low-cost alloy for low line frames and thin but stronger alloy tubes on more expensive frames.

Chainstays have heavier walls than the main tubes but will still vary in diameter and wall thickness based on the frames cost and intended use.

grumpus

I'd guess in the region of 1.5 mm depending on what grade alloy Specialized chose to use, they seem to be deliberately vague about that. Tube thickness is chosen for strength in the heat affected zone, so away from that it can be significantly thicker than it needs to be (higher spec tubes may be tapered or butted to compensate for that) so the middle of the stay may be thicker than it needs to be. The direction of the defect is also relevant - I'd expect a longitudinal scratch to be potentially less of a problem than one that creates a lateral stress riser. I'd just ride it and check frequently for cracks - take the wheel out and squeeze the dropouts together while looking for movement and listening for creaks.

Kontact 

It doesn't really matter. Either the scraped tube will last forever, or it will crack and fail in a non-catastrophic way. Chainstays break all the time on worn out steel bikes, and no one crashes because of it.

So you can either ride your perfectly functioning frame, or preemptively throw it in the trash. But there's no good reason to do the latter, and there's no repair that is going to help matters.

veganbikes

ALWAYS LOOK AT DATES OF THE ORIGINAL POST DON'T BE LIKE ME AND MAKE A ZOMBIE THREAD

Not sure as it can vary but more to the point are you the original owner and do you happen to have your receipt or can reach out to the shop and see if they have it you can file a claim. If you go to your local Specialized dealer they can help filing a crash replacement which can get you a discount on a new frame unfortunately they have stopped making the Langster a while back (my warranty replacement after a bottom bracket crack was one of the last remaining ones and I got lucky as it was the Rio edition) however you could put it towards something else in the line up. They can also look at the frame and help determine the viability of the frame in their eyes.

Like others have said it could last and be fine or it could fail. It is up to you if you want to take that risk or not, nobody else could make that decision for you.

Kontact 

Crash replacement discounts are nice, but since it's a 2004, Specialized is not going to have a rim brake frame to offer him. Which means that he'll need to buy - at a minimum - new wheels and calipers just to get a crummy mechanical disc set up.

Every time I went through this with a customer they usually just took the discount on a new disc bike and maybe replaced the old frame because they had all those rim brake parts. And that was with actually trashed frames - not little scrapes that might amount to nothing.

Keep in mind that most manufacturers are perfectly happy drilling holes in their aluminum tubes for cable stop rivets and bottle cage rivnuts. You have to remove an lot of material before a homogenous metal like aluminum becomes so weak that it begins flexing and stress hardening.

veganbikes

The Allez Elite is still rim brake and still being made and is a solid bike, though sadly Spesh doesn't do any fixed gear stuff anymore. They had the Allez Sprint Track but I haven't seen one of those for a few years. Regardless though it would be a swap to a geared bike at this point so wheel compatibility is out the door. However one could take the crash replacement get a sweet new geared ride for a bit of discount and then move parts over to a different frame as there are still plenty of fixed gear frames out there just not by the Big S.

Andrew R Stewart 

Well, this depends on where the material has been removed from and what else is in the affected area. Welds come to mind as a bad place to loose wall thickness (look up "undercutting weld edges). A lot of cracked frames are due to this. Andy

Kontact 

Of course. I wasn't writing a blank check that all damage is meaningless. I'm just trying to explain that the structure is much more resilient than we sometimes worry it is.

And, being a chainstay it is much less worrisome than a downtube/headtube junction. 4 tubes hold the back end together.

79pmooney

On steel, I've broken the right chainstay completely just behind the bridge and on a bike I bought used and abused, discovered both chainstays were about to break in the same place. First one I learned of while riding. Felt a little funky so i looked down and watched the chainstay waving around. (Yours is much stiffer. It won't wave.) Second I'd been riding a few weeks. Did notice that it was awfully easy to align the car displaced dropouts and rear end but missed the cracks. (I think that bike tried to stop an SUV.)

I'd just ride your bike and look at it periodically.

Ironfish653

How thick the tubing is will depend on which frame member it is, and what price point the bike inhabits.
The chain stays and seat stays will always be thicker walled than the main triangle, and a less expensive, recreational bike, like the Langster, will have thicker walled tubing than a high -performance bike like the Allez Sprint or a CAAD-13

either way, I echo the sentiment that bicycles are far more robust than they’re often given credit for around here

Koyote

The original post is 15 years old. I'm guessing that, by now, the frame has failed catastrophically and the poster is dead.

grumpus

Seems like that's at least the second necropost I've disturbed in as many months. Note to self: check OP date before replying.

veganbikes

Oh jeez I did it as well. frick!