tire question

I have a 94 regal with the 3.8 in it, its my winter car, I have a 94 firebird for the summer, it has 205/75/15 tires on it, the back tires are great, but I want to get snows for the front, I would like to get the stock 205/70/15s for it because they are both cheaper and the speedometer would be more accurate.. and it would accelerate faster.. but.. my father says that if I put the shorter tires on it, it will mess with the abs system. is this true? do I need to keep the same size front and rear? or can I put smaller 1s on the front