What must you check when transporting bicycles on a rear-mounted support system?

When transporting bicycles using a rear-mounted support system, it is essential to check three key aspects to comply with German traffic laws:

1. **Manufacturer's Instructions**: You need to ensure the support system is suitable for your vehicle as indicated by the manufacturer. This ensures stability and safety during transportation. If the system is not designed for your specific vehicle, it could lead to accidents.

2. **Secure Fixation**: It's critical to verify that the bicycles and the support system are securely attached. Loose bicycles can sway or fall off while driving, posing danger to other road users and yourself.

3. **Visibility of Equipment**: Lastly, you should check that the lighting equipment and number plate are not obstructed by the mounted bicycles. German traffic regulations stipulate that your vehicle must always have visible and functional lights and plates. If these are covered, it could lead to fines or accidents due to lack of visibility.

Addressing all these points ensures that you are complying with safety regulations and helps prevent potential accidents or legal issues while on the road.