I'm dealing with front end issues at the race track in a kart right now. My steering feels way too heavy and I want the kart to turn in faster and exit the corners faster. I was advised by a professional driver to remove a little caster and add a touch of tow out to the front wheels. This frees up the kart but makes the back end feel loose. I think the term here would be oversteer and I'm looking for a little more of that.
This must be the opposite if you want stability. As long as your top king pin angles sit behind the center of your wheels they will automatically straighten out when you let go of the steering wheel - kind of like, well just like the front wheels on a shopping cart.
The more positive caster (top of king pin pointing backwards) the more front end stability you'll have or "understeer" and this front end stability transfers to your rear wheels as well giving them more bite. The downside of understeer is how heavy it makes your steering feel in a corner.
In a kart you are in a very tight seat and you feel every move the kart makes and for me I found I prefer a little oversteer (less caster) which makes the rear feel a little to very loose but I control that. The benefit is the kart is faster going into and out of the corners and on a kart track there are a lot of corners!
In our cars you don't have that precise feel of control so I think adding more caster is a good idea - you'll have a lot more stability both front and rear but you'll have to pull the wheel a little harder and farther to get the desired effect. Make sense?
I understand there are caster shims but can't you add or subtract a little caster using the eccentrics on a VW? Seems to me the eccentric moved all the way back would add a measure of positive caster then bump the eccentric a little to the inside to give you a touch of negative camber. I'm so glad this topic came up because it's something that I'm trying to get dialed in as well!
@Jim Dunn You may have two issues going on. 1) The wind force is literally lifting the front of your car causing a "hydroplaning" effect (Not too likely). 2) You indeed may not have enough caster and the car feels uncomfortably squirrely at high speed. Squirrely doesn't necessarily mean you don't have traction it means your steering needs more attention and a very steady hand.
If you don't have enough caster your steering will feel light and responsive at any speed. Also, you may have enough caster but you may need to angle your body such that it pushes down on the front end at high speeds if you do that a lot. Or perhaps a touch of adjustment to both. These type of issues are tough to get just right.