Rarely do you want less downforce than max, except for F2007,F2010, and X2010. For everything else there is just 3 tracks you might want less downforce, Daytona, SSR7, and La Sarthe. For Daytona it is simple, can you go flat out without touching the breaks, then you might want a little less downforce. For La Sarthe, ie Le Mans, it is much more difficult, so you would have to do a couple practice runs in each car to find the sweet spot. If it is with chicanes you will very rarely improve your time with less than max downforce, but without chicanes is a whole other field.