Angle of pull
The car allows you to adjust the angle of pull the sheet has on the jib clew. Move the car forward and the pull is more downward which will tend to take the twist out of the sail and add camber. Move the car aft and the pull is more in line with the foot which allows the head to "twist off" and flattens the camber. Forward = power up, less twist, more camber used in light windsaft = power down, more twist, less camber used in higher winds.To point the highest you have to a) have the sheet as "inboard" as possible and b) the car as far aft as possible. Unless you are trying to point in choppy seas or in light winds in which case you will want to sacrifice some angle of sail for speed. This is where racers earn their money. Balancing the speed and angle of the boat with respect to the desired course for a VAST array of wind and sea conditions.I use the Newton method for lots of things to include car placement. Get the boat sailing upwind and going as fast as possible for a given course. Tweak each control in turn; Cunningham, sheet, leach cord, sheet car....... By remembering where the car was before the tweak and the speed then you can compare it to the new trim and speed to see if you did any good. if you got an increase then newtons method would tell you to move it more in the same direction until you see a decrease and then half the distance between the present position and the last one. You can take this kind of thing to several decimal places in the math world but practically speaking you are only talking about an inch or two of rope/car position so there is not much to do as you really can't adjust it (and tell the difference) when you only move the rope a millimeter. Then all you have to do is tweak all the other controls and since every thing interacts, start back at the beginning tweaking till EVERYTHING you do slows you down.