Seems like it's almost impossible to come out of the pit and drive on the Nordschleife like I do in AC as cars are super slippy and brakes perform horrible for a long while. Would love to be able to just launch and drive.
Try setting up a race with 0 AI opponents and a high number of laps or time setting. You'll start from the start line rather than the pits but your tyres and brakes will be warm.