It really depends on what you're trying to achieve. If it's for practice and getting a feel of the car and track then run the tires straight out of the package. You can run them down to the rim if you like. However, you'll notice the traction and stability will start to decrease. That said, you should keep a few things in mind 1: tires wear down the ride height goes down. Try to keep the ride height around 3.6-4.0 - depends on the asphalt. Check the tires stagger, what I mean by this is make sure the front wheels are 0.5~1.5 mm smaller in diameter then the rear. Always sauce the rears for 45-60 minutes, and fronts 5-15 minutes. This really comes down to your tire choice and traction additive.

For racing I would start at 43 front and 44 rear. Everything else I've stated above applies to race tires.

Hope this helps.