What do you have to expect after these traffic signs?

You correctly identified that the sign indicates a downhill slope of 10% grade lasting for 800 meters.

In German traffic rules, this triangular warning sign with a downward slope graphic and percentage warns drivers about a steep descent ahead. The additional plate below (800 m) specifies the length of this slope. This informs drivers to be prepared for continuous downhill driving for that distance, which may require careful braking and gear control to maintain safe speed and prevent brake overheating.

Remember, this sign does not indicate an uphill slope or that the slope starts 800 meters ahead, but that the downhill section itself extends for 800 meters immediately after the sign. This helps drivers adjust their driving accordingly.