Castor: Angle of the kingpin in relation to a vertical plane as viewed from the side of the car.
Increase the angle - Make the car more stable out of the turn as well as down the straights and increase steering entering a turn.
Decreasing the angle - Make the car feel more “touchy” at high speeds and help steering while exiting the turn. Less Castor – More front grip, more steering.
Lower Castor Angle – Better on slippery, inconsistent & rough surface.
Higher Castor Angle – Better on smooth, high traction track.


Reactive Castor – Amount of castor change when the front end of the car is compressing (diving) or decompressing (rising).
Increase the angle – Make the car react quicker & offer more steering.
Decrease the angle – make the car easier to drive smoothly into corners.

My experience is that with less static and reactive caster, the car tends to corner in an almost linear manner, holding a certain grip through the corner without a heavy turn-in or push on exit. More static and reactive caster tends to make the car "twitch" into the corner as you go off power, and then push a bit on exit. I would suggest less static and reactive caster for a flowing track, and more for a track (such as mine) that has lots of tight hairpins.

Just remember, what works for one car and driver might not work for another.