I just order some 215/45/17 bfg kdws for my oem 17x6.5 rims. What psi should I have them fill the tires to. I know that they will fill to the oem regulation but I know that they should be over inflated a little bit. Also, should I ask them to fill the tires with air instead of nitrogen? I plan on doing some autox events and I know i'll have to tinker with the tire psi later down the road. Is it ok to mix nitrogen and regular air?