The big bores are more forgiving and make the car more plush. They will make the car feel more lazy on turn in. I'm running on 100% clay and i've been using green springs all the way around with 1.6 pistons and 30 weight in the front 27.5 in the rear. My car has a slight under steer but it's very stable. Gray front springs and white rear is another good combo but it'll make the car more stiffly sprung. There are 3 pistons: 1.5, 1.6, 1.7 and the number is based on the diameter of the hole in the piston. A smaller diameter means that less shock oil will be able to pass through the holes. This will make the car have more damping and the holes will pack up faster so it doesn't bottom out as easy on big jumps. A large diameter is the opposite it will give you less damping, make the car feel softer, and it will bottom out easier over jumps. And remember the softer the car the more grip you'll create but a softer car does not transfer the weight as quickly.