Thursday, September 11, 2008

16 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.


  1. I broke a KORE bonded aluminum seatpost in a cross race a few years ago when I hit a bump. Ultra lightweight seatposts are not suited for cyclo-cross. The KORE post broke at roughly the same juncture as this AXlightness, execpt that it broke where the head clamp was bonded into the tube of the post.

    I would say the moral of the story is that if you want a seatpost for cross, make it all metal, all one piece, something like the Thomson Masterpiece or a Titanium Moots, really anything not carbon or bonded, maybe with two bolts in case one shears off.

    Keep the AXlightness on the roads.

  2. You have a point about application in Xracing. The Thomsons are some of the best seatposts I have seen strength wise. Atleast they ensure their saddles dont separate on failure through the "fuse". I would not buy a cladly built carbon tube to support AX lightness is certainly garbage in my eyes.

  3. Anonymous10:39 AM

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

  4. Anonymous1:21 PM

    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.

  5. Personally, I would use the Elite version of the Thomson seat post instead of the masterpiece. The only reason I say this is because most of the pros tend to use the Elite version.

  6. Yup, I think the MP and the Elite are virtually identical except for additional machining done on the body.

  7. Anonymous4:40 PM

    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).


  8. In engineering, specs matter. They really DO!! Now you can't go on designing a special seatpost for every single application, but on the part of the manufacturer, they should spell this detail out that 'hey, this post we would not recommend for so and so usage'. I personally don't see any advantage in decreasing 40 grams so I can sit on something flimsy that won't reliably support my body.

  9. Anonymous11:37 AM

    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?


  10. perhaps they should put a number rating system in place based on bending strength and what not, and they could show it on the catalogues.

  11. Anonymous12:09 PM

    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.

  12. Anonymous6:34 PM

    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

  13. Anonymous10:47 PM

    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.

  14. The two clues to not buy or use this seatpost are

    1-- the clamp is designed to cut the saddle rails (Look at the photos.) and

    2-- it retails for 500 dollars.

    Since the best seatposts -- prettiest, strongest, longest-time-tested -- sell for less than a fourth of that, the retail price is a flag that says, in large neon letters, “This is a piece of crap.”

    Bob Cooper

  15. Anonymous9:09 AM

    Carbon fibre wank. Yeah you might get an occasional bump on the road which, combined with other factors may result in failure. But seriously...using a AX lightness post for CX?? No brainer.

  16. Weight weenies have always been fools hypnotized by saving a few measley grams


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