taken from wiki manual...
So a higher coast setting will both reduce the chance of a single wheels locking up under braking, and the difference that lift-off oversteer makes to the car balance. Likewise a higher power setting will reduce the chance of a single wheel spinning under power but will increase power oversteer in RWD cars. As a rule of thumb, having the power side set low and the coast high makes a car easy to drive, while high power and low coast is fastest – so adjust to your skill and taste.
basically,if you increase the coast figure then its easier to control under hard braking BUT you will lose some braking performance from the engine.i normally use between 40-70 depending on car and track.
if you have a lower setting on power,it will make it easier to drive out of corners but some power may be lost through the unloaded tyre breaking traction and spinning up,i normally keep it between 25-50.
if you have big gaps between ratios,when you shift down it can cause the driven wheels to lock,when turning in on a rwd car,sometimes it can help a little to reduce understeer,again car and track determine your setup.
im afraid they arent many setups that work on all tracks,the differences can make a big difference on certain tracks.
Tango