The vehicles ahead of you are driving at about 30 km/h. Why are you not permitted to overtake before the road bend?

Your answer is fully correct.

You are not allowed to overtake before the road bend because your overtaking distance is too long. This means you would need more space and time to complete the overtaking safely, which you do not have on a bend. Additionally, the red car ahead might pull out to overtake, which poses a risk of collision if you also try to overtake at the same time.

In German traffic rules, overtaking is only safe and permitted when you have a clear, unobstructed view of the road ahead and enough space to complete the maneuver without causing danger. On or before bends, your visibility is limited, and you cannot accurately judge the actions of other vehicles. This rule helps prevent accidents caused by misjudged overtaking attempts.