I normally start my tires at 1.85 in the back and like 1.78 in the front for club racing. any larger and you will chunk much easier and the traction will be all screwed up, you normally cant run them that high at big races since you will have wayyyy to much traction. Also i make sure to have under 4mm of ride height, however normally i run under 3mm's of ride height since the car does handle better the lower you go (thus you have to adjust ride hieght to get em at the correct hieght)