I'd keep your tyre pressure's at at least 30 psi, if its a cold day or raining you wont get enought heat in your tyres and you'll just slide around or roll the tyres of the rims. Take a tyre pressure guage with you and when you start to push the car hard for a few laps then check the pressure, try to keep it about 30-36psi. I doubt you guys will see much of a pressure increase as this couse is only a beginer thing and you wont have helmets so i doubt you'll be able to push your cars very hard.