got a set of iceage antistab and avid drivers on the anti stab how far back from the leading edge of the wheels should the rails be cut back I cut a nice smooth rounded edge but their only recessed a quarter of an inch or so and for the drivers how loose can you run the track or should I just stick to spec? on a side note I have 2.86 pitch 7 tooth drivers and want to figure out my final gear ratio have 20 40 gears so that's 2.0 but don't know how to figure in the drivers any advice is appreciated thanks!