+2 Depends on the track, dirt (region of the country), track maintenance, whether they run 1/8 scales, etc.
But in general, a wide variety of pin sizes for the rear. Perhaps a set of Step Pins for rough loose dirt tracks typical of the midwest. (Guessing from your indoor comment.) And some small pins, such as Losi Taper Pins, if it's a smooth relatively hard packed track. ProLine Holeshots frequently seem to be OK.
But best advice is to try and ask around at each track or surrounding Hobby Shops. If you have track contact info try calling them, they should know what works.