[autoavia]

Tracks get a layer of dust whenever they are not used for a while so it is possible that it is not Ortmanns causing lack of grip. If I forget to vacuum my track then all tyres pick up some dust and need cleaning after a few laps. Soon sorted with some sticky tape.

 The track is covered between club nights and it is only after we have run vintage with ortmanns that we get the grip problem. Maybe because vintage cars, particularly 1/24 scale tend to be much heavier than modern cars they wear the tyres faster and produce more dust. Most vintage cars also run much wider tyres than modern cars so more tyre area to produce dust. 
 I have tested modern cars with other urethanes during club nights and no one has complained of loss of grip when they followed me onto a lane which led us to conclude that Ortmanns on vintage cars are causing the problem.