Admit it, drivers buy the 15" BFG m&s 's for the "look" and they also serve to keep the wheels off the ground
. Definitely not performance tires.
Your cold tire pressures depend upon the tire manufacturer's recommended hot pressures, your car's setup and the driver's preference. I'd suggest you take the car to an auto-x or 3, and experiment with different pressures.
Regards,
Bob S