Jimmy how are you going about finding out what surfaces are what ? Quick look in BagEdit shows oval2 (speedway2 base track) uses urban01 for the grass surface. When I first was learning to mod I tried changing the name of the material in bagedit but it had no effect, but not 100% sure i was doing it right either. After doing the same in 3ds max to material name and it worked, I never tried this again. I will play around with it some more tomorrow to see if its possible to include the speedway2 and tarmac03 .scne files in your surface mod with one of the other offroad surfaces assigned to grass and sand.