Broken KH frame

Yeah go for the white russian…

2 month riding by a 13 year old guy

Have you ever heard of, “heat effect zone?”

P.S. This is void if the frames are heat treated post welding.

Joe, it’s “heat affected zone,” and he’s completely correct in his initial statement. The weld didn’t break, the metal around it did. That means it is adequate. Furthermore, as far as I know, all aluminum frames get a post-weld heat tempering to relieve stresses. Even if KH frames didn’t, off of them would have approximately the same quality of welds and tubes as eachother. If the weld were seriously weakening the tube, we’d be seeing more frames break because of it.

That said, I seriously doubt it’s a “deficiency in the alloy” or some crap like that. Taiwan has aluminum smelters which put out aluminum as good, or better than that which the US makes. Furthermore, if it were a defect in the alloy of metal, we’d be seeing hundreds of KH frames break, since factories do production runs by cutting hundreds of frame parts from one extruded tube.

Evan is right. This stuff is simpler than y’all make it out to be.

The frame was ridden hard. We all know aluminum frames have shorter fatigue lives. Live with it, fix it, or get a different model.

Hahhahahahaa How the hell did that happen? HAhahhahaha.

Broken Frame

It seemed that the Frame was pretty new (It was a 2007 model. How old could it be?). I did not see hard wear on it. I stated above that the weld was of good quality. The aluminum might have been fatigueged but that usually only happens after a few years of hard riding. the most likely cause of the break was a big trick with tons of torque put on the frame. Very easy especially if the seat post is long. Or weak metal at that point. This could be coused by a number of reasons. A worker throwing a cigarette but into the metal bath or any other impurity being introduced, bad mixing of the compounds, uneven cooling of the molten alloy are just some of the factors that could cause such a streak of weakess in a metal. The unicycle manufacturer is not to blame in theis instance. It is either the alloy smelter or pipe forger.


Do you know how it broke? Many abuse koxx frames and they hold up fine. My guess is it that it is either a really good 13year old or a messed up frame. Things like that are very rare other wise we would hear about them much much more.

theres been quite a few reports of the koxx devil frames - later models - breaking. The french forums have quite a few of them. people here dont really ride koxx thats why you dont here that much about it.

First off I’m sorry I spelled it wrong.

Secondly it looks to me that on the back side of the uni it broke right on top of the weld (which IS in the heat affected zone, if there is one) but it’s hard to tell where the crack started from with only two low quality pictures to judge from.

P.S. I’m always egar to learn so if my theory isn’t worth a crock of beans dont be afraid to tell me so.

I agree 100% that the combination of those factors (plus maybe frequent awkward landings seat in) is likely to cause that failure, but also may have been a slight defect in the frame that contributed.

Well, since it’s the manufacturer’s responsibility to make sure they have good reliable suppliers I’d say it is KHU responsibility, if this is the case.

Joe, your theory about heat damage around the weld is plausible, except this is a production frame that’s already been through a few revisions. A problem like that would have shown up immediately.

You can tell approximately where the crack started based on the shape of the broken metal. Note how there’s a sort of tab left from t he seattube ont he back of the crown. That was the last part to break. Hence we can take an educated guess that the crack started in the same plane as the end of the crack, and thus started on the front of the seattube. Clear as mud, eh?

However, Unicorn’s theory is still a load of crap, to put it bluntly. Intentionally contaminating an aluminum melt is grounds to be fired on the spot, even in union foundries (which I doubt this Taiwanese place is). Furthermore, the aluminum is completely enclosed during the melt. The uneven cooling point is moot because aluminum goes through a number of careful heat-treat cycles after the initial casting. The local impurity theory is incredibly unlikely. The only feasible answer is a contaminated weld, but then the weld would have failed, not the surrounding metal. Whatever though. Arguing further would be like trying to argue with people who dispute the moon landings. They’ll believe what they want to believe.

You don’t actually believe that man landed on the moon do you?
Next you’ll be saying we live on the outside of a ball . . . rather than inside a hollow earth.

To quote South Park "Dumb da dumb dumb dumb . . . "

Failed Aluminum Tube on KH

Gerblefranklin - Thanks for saying that I “dispence a load of crap”. I threw out a few LIKELY reasons for the failure. I did not say that it was any one of them. I work as a manufacturing engineer in the electronics industry. In the past I have done loads of studies on failed solder joints. In most instances they fail because of bad soldering processes(incorect heating levels or times.) or contamination. Now, I agree with you that a worker contaminating a process intentionaly should be fired on the spot. I did not suggest that the contamination was intentional. However I have seen such things as hand lotions that female workers wear prevent solder from attaching on to a circuit board! I have also recieved numerous University lboratory report of impurites in the metal alloys of components that are made in batches of hundred of thousands! In my post above I stated that either the guy did some huge trick that put too much force on the uni or that the Alunminum pipe was defective. This is truly the case. The weld help up.


That’s fair, but I still don’t see how it would be one single frame to fail like this when these are made in significantly larger production runs. Once again my words were harsh. Sorry. I think I did make enough points in my previous post to explain why I disagreed with those potential causes of failure, though. Whatever. I’m always an asshole when I post in threads like this, so once again, i will apologize.

To clarify. We agree that mistakes can be made on a large scale, and that in fact the frame could be made from a bad extrusion. But if that were the case, we would see the same problem in hundreds of frames, not just one. That is why I’m adamantly disagreeing with anything that points at a problem with the process.

I think we ultimately agree on the cause of failure though. Excessive stress from some trick…

Yeah. He landed on the moon.

Is it so hard to belive that when too thin of a seat tube is used, that it breaks with use? Maybe nothing was wrong with the metal at all? Gasp!