To get Maximum vehicle stats, press: SQUARE, L2, X, R1, L2, L2, LEFT, R1, RIGHT, L1, L1. Notice that it doesn't say "Cheat Activated", due to it might be a secret, but since it doesn't say "cheat activated", check the stats, and you will notice that Bike Skill, Cycling Skill, Driving Skill and flying Skill will be full.