Friday, September 12, 2008

Ax-Lightness Daedalus Seatpost Failure

Forget testicular cancer!

Imagine your bum just rose in standing to pedal up to the top of that hill. You sit back down and discover that the saddle is missing!!! Except its too late, the post may already be in your intestines.

A carbon seat post failing and opening up something of that possibility constitutes a conspicuous disregard for engineering ethics and safety, especially if the load didn't even exceeded the max spec. That should never happen!!

Weightweenies member Roberto Bicicletas
says : So, about two hours ago, in the middle of a cross race in Herne Hill (London UK), I found out I had nowhere to sit on my bike anymore . Didn't get hurt, but my heart feels broken - I am a 72kg cat4 club rider, way below the weight limit of the seatpost (85kg), and the seatpost/bike never been involved in a crash.

What you're looking at is possibly the lightest setback seatpost on the market. Notice the failure just where the post curves out, at the point where the AX logo was dented in. Possibly a delamination. There is little room for flex. Often on bending, fibers fail at low strain values.

The retail for this flimsy product stands at more than 500 dollars. Thats not the kind of price for an injured bum, and a broken heart.

More pictures on Weight Weenies.


Anonymous said...

i've seen this type of situation in funny films, not so funny when it happens to u in real

Luis Diaz said...

Carbon is usually fine for cross, depending on your weight and how you ride.

The lightness seatpost has no place in a cross bike. This is the fault of the rider for making such a silly decision.

Anonymous said...

great blog! this is a good example of an improper application of technology (on the rider's part). the mere existence of a light weight CF part doesn't mean it is suitable for all applications. we now see that this post has a razor thin margin of safety. echoing the other commenters, stick with a robust design for cx posts (no bonded aluminum - i've killed two DA bonded posts and one Kore bonded post; and no dangerously light CF posts).


Anonymous said...

your bring up a good point ron. i suppose the responsibility falls on the mfg to provide usage guidelines. the general (non-engineering) public may not consider the limits of a particular design for a given application, or the trade-offs that go into making a light-weight piece of equipment (as witnessed by this guy's use of the ax lightness post on a cross bike). this seatpost is an obvious case, but i think such usage guidelines may become confusing to apply (for mfg's) and to interpret (for consumers) unless an industry standard is adopted. i wonder what such a standard would look like?


Anonymous said...

That post seems to be under engineered. Why is it so costly to produce if its using such less material? I find some discrepancies in the biking industry hard to understand.

Anonymous said...

I wonder if that design ever passed th Fatigue Test - DIN, or the DIN+?
What is really surprising is that the EN Fatigue Test has effectively doubled and everything that is now sold in France is required by law to pass this test.
Did they pass the new EN?

- Ryan

Matt in Denver said...

Yeah tolerances matter! When the mfr specifies an atypical limit (I'm thinking of all those cheesy wheelsets and frames with 185 lb limits), I've always just rejected them because I don't want components that have tolerances that might just barely work, I want the tolerances to exceed the worst-case stresses they are likely to encounter! Whoever makes that AX seatpost should probably not make airplane wings.

If a desinger achieves some weight objective with a product that fails to meet standard tolerances, then that design is a failure.