bob barry, i am currently testing my tc4 with different spacer thicknesses. for example the tc4 comes stock with .025", .050", and .075" i'm trying out .030" spacers ... so basically i'm running .060" all around in front and .090" all around in rear and let me say that my car is handling great but it also ran great with the stock ones so i guess try it all and stay with what is faster.