Handlebar and stem are the number one causes of accident. Often, they are not seen as a unit and combined the wrong way. A stiff steel stem, for example, does not only pass all deflections on to an elastic aluminium handlebar, but also notches it slowly but surely. This happens unnoticed, the handlebar breaks without advance warning. Milling traces and notches imperil every component and often cause breaking.
Another dangerous weak point of the bike is the fork. Ist he fork thread too long, the stem clamp is still in the thread section. The thinnest part therefore is stressed the most. Dirk Zedler rejects aluminium columns in general. Modern brakes are so powerful that forks and rims can hardly sustain the stress. Accidents caused by fork failure are the worst according to Zedler's experience.
Also mudguards are critical points. If, for example, a branch gets cought in the mudguard, it is torn away by the tire, folds up and gets wedged underneath the fork crown. The front wheel is blocked quick as lightning, the fork snaps, the rider tries to hold on to the handlebar an hits the ground with his head. Meanwhile, several manufacturers offer holding devices releasing the mudguard stays in case of emergency and avoid a blocking of the wheel.
Often, particularly minor negligences have bad consequences. Although rim tape, e.g., is not very expensive, some manufacturers use anything from rubberband to insulating tape.
Dirk Zedler thinks that many sources of danger could easily be detected when having a close look. Only by visual control a bike expert could eliminate 80 percent of all risks, without a test being necessary. Zedler makes an appeal to manufacturers: "Check a bike before starting serial production. Be particularly careful when it comes to components which are important for the safety of the bike and do not change the combination of a running production series, depending on which components are in stock. And if the manufacturer overlooks weak points despite all care, the dealer should be competent and capable of noticing them during the final check and put the manufacturer under pressure.