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also depends if you want total traction or just enough to get you going ,I've used just plain sheet metel screws ,50 on the rear and 25 on the front ,more serious racers use like a 100 per tire
do you have ice screws or sheet metal ?and there can be a point of to many if you are driving on other things besides ice ,the angle of the slot in the screw head can affect traction also .
I know that yo have to look at which way the slots are sitting ,and if they get any rounding going down your drive then that will take some of the edge off