Generally, the MAX SPEED LIMIT on glider trailers in Germany is 80 Km/hour.

Not true! Most glider trailers have been approved for 100km/h by now. In that case, they must place a white, round plaque or sticker with a black '100' on the tail end to indicate to the cops that they are not speeding when doing 100 with that trailer.

However, the approval to 100 Km/hour is only 62 MPH.
In the USA speed limits on the Interstate highways are 65 to 85 MPH.
My point is that many of us are driving too fast to rely on just a brake system . . . adding substantial chains might help save your sailplane at all speeds.