I've reviewed multiple videos of shooters, not all FIRST related. Also this year we've prototyped with different surfaces, wood, aluminum, foam, etc. Seems there are a lot of fine variables, between surfaces, both of wheels and walls, but also the amount of pressure placed on the disk. It's an 11" disk, but 11" of space doesn't give you the optimal velocity. Proto-type different things and find what works best for you, and remember 1/16 of an inch between the wheel and the wall can make a huge difference.
WHEELS: Solid, rubber, wrapped in foam, treaded....don't be afraid of trying different surfaces, it's almost fun to see the differences.
Good Luck