There's no definitive answer for tire pressure. Lots of variables involved such as what tire you're running, weight of car, driving style, or even road surface. Typically we chalk the outside edge of the tire so we can see how far over the tires "roll over" so we can reduce the pressure as low as possible without rolling over onto the sidewall. Maybe start at the factory recommended pressures located on the sticker on the inside of your door and adjust from there.
Highly recommend getting a tire pressure gauge that allows you to adjust pressure while measuring. You'll probably need to let some air out between runs as the pressures increase with heat.
Hope this helps a bit.