Actually, a seat post's task seems to be quite simple: It connects frame and saddle and allows for the rider to find his/her individual position on the bike - provided that the seat post can well be adjusted in length and angle. You could assume that this task can be fulfilled quite easily - but time and again seat posts break causing bad injuries. When examining these breaks, the damage can roughly be devided into two categories.
One is very mixed: Neither material nor weight, price or construction of the seat clamp structure the damage; seat posts burst directly at their frame exit or somewhere in the middle of the tube, clamp heads or the shell of the holding mechanism break. Faulty construction can just as well be the reason as faulty assembly.
The other category, however, is very clear: In it, you find the classic patented seat post. One single bolt clamps the saddle - and it breaks. This is by far the number one cause of accident.
Short and crisp
The seat post is a sensitive component, which needs accurate assembly with proper tools in order to work durably and safely. Seat posts with double-bolt-clamps are preferable, but they also need to be tightened with the right torque. The construction principle of the patented seat post with only one bolt to clamp the saddle with is generally problematic. It is negligent not to use a torque wrench.
Crashtest-safety and occupant protection nowadays are major development goals and offensively advertised sales arguments with cars. The trend of more safety seems to pass the bike tracelessly, though bike riders are exposed to the dangers of road traffic much more directly. How else could it be explained that in the form of patented seat posts a construction principle is sold millionfold which according to reputable engineering has to be assessed dangerous? When using patented seat posts, the saddle and with it the rider's safety hangs on one single bolt which is furthermore stressed improperly at inflexion. The problem can at best be controlled when tightening the bolt tight enough with a torque wrench. With a normal hex key or minitool most people cannot generate enough strength. The seat post can hold, but does not have to - the danger of breaking always is a fellow passenger. Show responsibility and ban patented seat posts from your bikes!
Author: Graduate engineer Dirk Zedler, bike expert