my general rule of thumb is a 700' line in the middle of the track.if you are building a super mod only track your turns are gonna determine that, some guys like big wider corners and a narrow straight ......1/8th is a good starting place then you can always punch the corners out more.I like putting about 5-10 degrees bank in 1 and 3 so the fast guys can get slideways and open up 2 and 4 to get into the straight.