A quick warning. Check yer bars!

The previous crash may have had something to do with it, but Id be more looking at the bolts on the stem being overtightened , You dont want to be introducing areas of uneven stress into aluminium.

Glad to hear your okay , not a fun thing to happen at all. Thank god thats never happend to me.

Aluminium alloy parts in particular are also susceptible to fatigue failure. Even if components are correctly fitted and haven't been crashed, they can fail after sufficiently vigorous and/or prolonged use.

I've had two sets of handlebars snap while riding. I came off on both occasions. One of those spills cost me a broken collarbone and I was lucky that it didn't cost me my life, as I went skating through a red light on my ear out into the middle of a busy T-junction.

I now replace my bars and stem every few years, regardless of how healthy they look. It seems odd to retire components that look just fine but I regard it as an insurance cost.

IIRC, about 15 or so years ago there was an increase in the number of MTB XC riders reporting broken stems, bars and in some cases, seatposts. I believe that component manufacturers had taken the weight-weenyism just a little too far.

I snapped the Alu seatpost On my old hardtail.
Showed no signs of wear and there was nothing that could of caused it to weaken, no bad falls putting stress on it or the likes.

Parts just seem to diminish after a few years of use.

Good to hear you survived relatively intact. Does look like a failure due to overtightening the clamp. I have a free torque wrench coming with the new bike. Before I just used 'the force' to tighten bolts, usually a quarter turn more after it stsrts to tighten.

Strange, the way we try to get away with not using the correct and not so expensive tools on our costly bikes. A bit like sticking a 20 or 30 euro lock on a bike worth a grand!

'68 wrote:

Thanks for all the comments, didn't want to worry anyone. Just to clarify, it's an ITM alu bar in an alu stem that's about 5 years old and has been crashed twice before. It really is my own fault, I should have paid more attention to my maintenance routine. It's my commuter bike and doesn't get half the love it deserves.
I'm sure that over torquing the stem nuts played a part but I'm certain the two previous crashes did the majority of the damage.

Have a look at the grain of the metal, if its smooth over a part then suddenly rough thats a prime example of metal fatigue.

'68 wrote:

@Kona. The top half of the break looks really clean. Then the bottom half looks like it tore away. Is this what you mean?

Yup exactley what I mean. Metal fatigue is your culprit!

'68 wrote:

So was it the crashes or the bolts?

Aluminium is suspect to metal fatigue and has a definate life cycle. An example being the airframe of a aircraft, its only rated for so many cycles. Overtightening and crashes or sharp edges will lead to introduction areas of stress into the metal, its these areas that slowly grow into cracks, and over time it breaks, as you have seen. Usually you can catch it by inspection, but its hard when there is paint etc covering the metal.

Only thing you can do is inspect the parts for signs of fatigue, its the little things like this ,where a good mechanic earns his money, even if you have any mates that are mechanical engineers or deal with materials, they will be able to see the common points where fatigue will begin. Or even if you take a read of a materials book for engineers, it goes into depth about fatigue. Fatigue is a serious issue with metal failure.

IMO it was a combination of age, crash and bolts that caused it.

'68 wrote:

Thanks for all the comments, didn't want to worry anyone. Just to clarify, it's an ITM alu bar in an alu stem that's about 5 years old and has been crashed twice before.

Hmm, I did the same thing to an ITM bar some while back. I reckon it's all the power we're laying down... :cool: