




TOUR 12/2018

“Failing within the standard is unacceptable”

Graduate engineer Dirk Zedler is a publicly appointed and sworn in expert for bicycles. He is running an institute for bicycle technology and safety in Ludwigsburg where our seat post test was performed

TOUR Do the damages found during the test also occur in reality and are there any tips for the selection of a seat post?
ZEDLER We as witness experts are familiar with the defects that occurred during the test from expert’s reports for the courts and the insurers; they actually do occur like that in the field. Nevertheless, we were surprised by the big number of failures among the high-priced products, because we performed the tests strictly in accordance with the globally recognized minimum requirements of the ISO standard and subsequently according to criteria with which we have been working successfully for many years when testing clearly less expensive seat posts. Failing within the standard or shortly after is simply unacceptable. The super light MCFK seat post, the comfortable Specialized and the very long Syntace endured much more in the second run, i.e. the TOUR test, with higher loads, even after having been preloaded with repeated tightening and also too high torque values applied in both clamping areas. These seat posts have significant safety reserves, even for athletic and heavy riders.

That means that defects are less frequent in the case of less expensive seat posts or aluminium seat posts?
In the case of aluminium breakages at the clamp hardly never occur and if so then due to corrosion. However, the bolts of cheap seat posts are concerned by breakages; more details can only be determined with a test.

How can I detect an imminent defect in time?
For some models the defects in the frame’s clamping area is certainly due to the length of the seat post, a long extension creates enormous tensions and movements. With shorter posts this should be less critical. The positive thing is that none of the bolts broke, i.e. that the heads are all designed in a smart way and none of the posts exploded like in the test performed a few years ago. Some seat posts were affected by cracks and thus lost stiffness and became soft which was detected by our testing systems. Road racers are not as sensitive as that; therefore regular visual checks of the seat posts in bright light are a must if something feels weird or cracks. Discolourations, deformations and haircracks are warning signs. The seat post should be replaced.

What should be considered for the handling of carbon seat posts?
One should never work on carbon seat posts without carbon assembly paste and torque wrench. Another crucial thing is to observe the assembly instructions and marks printed on. However, a seat post should always be observed within the context of other components. The clamping slots of some frames are sharp-edged and can lead to damage. A turned clamp already, as prescribed by some manufacturers, can alleviate the problem. Further dangers are at the seat post head: Breakages of short saddle clamps demonstrate the high forces acting in this area. These also weigh upon the saddle rails - in particular rails made of titanium or carbon may break. The longer the half-shell in the bottom area, the more gentle is the distribution of forces on the saddle rails.

INTERVIEW Jens Kloetzer


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