John,

Oversteer, occurs when you are in a turn and the front wheels do not follow the turn radius but instead push (shovel) a different radius. More rubber up from helps reduce this affect by helping he tires better follow the steering line.

 

Chad, I think you mmean under-steer. Oversteer is when
the back-end comes around because it's not sticking
as well as the front. More rubber in the front will make
the fronst stick better. That's what you need to cure
under-steer, which is when you turn in but the car ploughs on
in more of a straight line than you want/need.
"Ackerman" is a property of the geometry of the front steering
system. When you turn your steering wheel from straight ahead
to go around a corner, let's say the outside front wheel turns
in 30 degrees. A zero-ackerman setup would also turn in your
inside wheel by the same amount, but that's not what you want!
Your inside wheel is closer to the point you are turning around,
and needs to turn in more to contribute to turning. How much
more depends on the radius, but there's no easy way for a car
to know what radius it's turning at, so most steering systems
dial in a fixed amount of ackerman (per degree) Ie: the inside
will turn in some small fraction of a degree more for every degree
the wheels are turned in. To be more technical, Ackerman is the
amount of induced toe-out while turning. I do not immediately
understand how a change in tire radius would affect Ackerman.
Lastly, ABS only knows how fast the hub is turning. It can't
differentiate whether the car is going 65mph with tire A, or
70mph with taller tire B. As long as the tires are rotating at
the same RPM, ABS and the viscous unit are happy. For ABS, the
only issue is RPM difference. If you change rubber to make one
end stick substantially better than the other, then the only affect
is that ABS will still limit effective braking to what the weaker
end will support without lockup.
Joe