i am planning on putting a balloon strip around at least the back wheel and most likely all wheels, to avoid any spinning or skidding (as this would throw off the run).
Its running on a tile floor so the balloons will help
http://www.chiefdelphi.com/media/photos/28597
that is the car i made for my senior year physics class in high school.
as far as materials go we can use anything we can get, no cost limit just as long as nothings radioactive. And being part of the Iowa State solar car team, i am definitely making a carbon fiber spoiler simply because we have a large scrap pile of it...