Mountain Bike Reviews Forum banner
1 - 15 of 15 Posts

·
Registered
Joined
·
472 Posts
Discussion Starter · #1 · (Edited)
I am getting the impression from my research that tubes don’t fail. Welds fail, if there is a failure at all.
is this a concern still today?
Or have all the builders got this correctEd/stopped with know how and proper equipment and environment?
Is steel usually the weld also? Or rust or dents, crash damage etc.
am I wrong? Thank you.
 

·
Registered
Joined
·
44 Posts
I have had three titanium failures and three steel failures. In both cases, two of them at the downtube about one inch from the weld and the third on the brake fork leg at about two thirds of the leg height.

 

·
Registered
Joined
·
222 Posts
It's also true of aluminum. There is a heat-affected zone that weakens the area around the weld. Usually the weld itself is stronger than the surrounding metal, just by virtue of having more material (all that extra filler adds strength), but the edges of the weld are the weakest point.

If you google for "broken titanium bicycle frame", you'll note that pretty much every image shows a crack that either follows the edge of, or starts at the edge of a weld.

The only material that doesn't break this way is carbon; usually they break from a point of impact, or they'll delaminate somewhere random where there's a flaw in the layup.
 

·
Registered
Joined
·
39 Posts
My experiences with frame failures are all about halfway between the HT and bottle bosses on the down tube.

Aluminum, Steel, Titanium — only 1 was my personal bike (and a BMX so that doesn't really count)

I have yet to see a bike (in person) that has failed at the weld.

I will also say that these have all been late 90s early 2000s frames and a few of those frames were produced in the same year in by the same American/high-end brand (makes me think that there was an issue with the machine making the tubes).
 

·
Wanna ride bikes?
Joined
·
12,534 Posts
I am getting the impression from my research that tubes don’t fail. Welds fail, if there is a failure at all.
is this a concern still today?
Or have all the builders got this correctEd/stopped with know how and proper equipment and environment?
Is steel usually the weld also? Or rust or dents, crash damage etc.
am I wrong? Thank you.
Pretty vague. Are we talking about an off the shelf asian made frame, a custom ti frame, or???

Heat effected zones are always hot spots for cracks to form, but the reasons are various when comparing different frame materials. I don't think ti frames are any more or less susceptible to cracking there than any other frame material. (tough to say for sure given the number of ti frames out there compared to aluminum and steel)

I've broken 5 frames, roughly 60-70% were at a weld, others were just over-powered and apparently I exceeded the intended purpose for that tubeset. (one was a custom steel frame, also Surly, Jamis, Kona, and Motobecane)

The bottom line is if you're not exceeding the design and build quality of said frame this is all trivial, your frame will last a long time. If you have a history of breaking frames or are on the heavier side, then you need to be more specific and give details to get good answers.

Ti cracks in weird ways that are different than aluminum and steel in some ways. The good news is it's fairly easy to repair.
 

·
Registered
Joined
·
1,619 Posts
sgltrak, thanks for the picture; did you have it repaired (very difficult with Ti since the area needs to be cleaned meticulously, then re-welded in an inert atmosphere). My friend had a BD Ti frame that cracked at the BB, and wasn't feasible to repair.
 

·
slow
Joined
·
8,157 Posts
sgltrak, thanks for the picture; did you have it repaired (very difficult with Ti since the area need to be cleaned meticulously, then re-welded in an inert atmosphere). My friend had a BD Ti frame that cracked at the BB, and wasn't feasible to repair.
Moots generously offered a crash replacement, even though I was not the original owner, but I had it repaired locally and it held for another season. The photo below is of the repaired frame. Unfortunatley the crack started to show up again through the repaired welds, so I have relegated the frame to gravel duty.

My understanding from visiting with a couple of frame builders is that the stresses of a joint like this with the top tube and down tube intersecting before joining the head tube causes additional stresses to this area and it seems that most builders are now using a taller head tube than before to allow a full weld around the circumference of both the top tube and down tube at the head tube. I ended up buying a larger version of the same frame and have not encoutnered any problems since.
http://instagr.am/p/BnKWKTOhH_b/
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top