I set my diff till it barely slips in my hands. Then test on the track. If it goes when I tell it to, then it's good. If it seems sluggish I tighten it till it doesn't. Then if my setup is good but still feels a bit "free" I'll snug it a lil more. But the best thing I've learned so far is keeping notes like I do when I race off-road. I figured since it's only 1 car I'm racing, I didn't need to keep notes. But ya definitely need to. Especially from day to day, this way I can eventually get a feel for the adjustments I make and why.