We only raced inside on wim as it was raining so heavily on sunday morning.
The surface is now dirt impregnated with chunks of rubber (not gravel although it does look like it) like the marbles on an f1 track. We had to do a lot of sweeping. The rubber makes it quite bumpy. I had a chunk of rubber jam my steering in one heat. This was much better after the cars had cleared a line.
There is another post running on this subject on the Tiverton section