LABORATORY TEST – The tests regarding the fatigue behaviour of the seatposts and their flex behaviour were conducted at the testing institute Zedler (www.zedler.de) in Ludwigsburg. First of all, each seatpost had to comply with the requirements of the ISO standard 4210. That included 100,000 load cycles of 1200 N applied behind the middle of the saddle clamp. Subsequently the test samples went through a practical test spectrum developed by the Zedler institute which introduces not only higher loads up to 1700 N, but also individual loads to the saddle nose. The loads are to simulate a useful life of the seat post over several years by a 90 kg cyclist during intensive tours. The chosen extension length was 27 cm, i.e. quite close to reality. More details at: www.bike-magazin.de (...).
Dirk Zedler, graduate engineer, bicycle expert
"Claims regarding seatpost failure are nearly regularly on the agenda of our daily routine of writing expert’s reports. There are basically three damage mechanisms. The most frequent one is the failure of the bolted connections. The movements of the saddle partly result in inappropriate load acting on them. In this case the reserve is inferior, already a slightly too low torque value can result in failure. Fractures in the area where the seatpost comes out of the frame are quite rare. This is particularly due to the too low compressive strength of carbon tubes and to unfavourable clamp mechanisms on the tubes. Often the clamps are overtightened on the tubes. The least common are fractures in the middle of the tube or at the head. During the operational strength test it was made sure to observe the torque values which did not tighten the seatposts in an unfavourable way or overtightened them.
The test criteria are above the ISO standard, as the minimum requirements of this standard do not include harder service. BIKE real data collections revealed that a cyclist is pressed into the saddle with an increase in the acceleration due to gravity when riding through a compression. An 80 kg cyclist brings about 50 kg on the saddle depending on his position, which corresponds to a short-term load of up to 2000 Newton. With our test loads we have remained clearly below."
