Originally Posted by Mike Rainbird

The more caster you have, the more straight-line stability and the more negative camber you get with steering lock and the outside wheel during cornering (with the inside getting positive camber). This aids turn-in, but you can go too far, which could cause drive shaft problems with a 4wd. Also it makes the steering heavier, so the above range is considered to give good straight line stability along with reasonably weighted steering and not too much camber change .

With positive caster, you also get some self centering of the steering wheel, which is a good thing for drifting (once on full lock, you can actually let go of the wheel, and it will naturally straighten ).