Ok, the shimming of the spring on my van resulted in an improvement in
traction.  Subjective?, hell yes.  I have no lap times to gauge against, as
is the case when you change a suspension setting on a race car.
  I do have the same driveway (about 1/4 mile of gravel at about 6% with a
few pitches at ~10%) that I've been driving up and down for a year in the
van.  Now, I have less tendency to lose traction on the steeper sections,
even if I don't 'get a run' like I have been doing.  Also, the wheel that I
shimmed (right rear) doesn't start hopping over the low spots...
  I think I've made a move in the proper direction, trying to add some of
the vehicle's weight to that corner by shimming down the spring seat about
1/4", so far...
  Subjective, until I take the Van to the Nuremberg Ring or Laguna Seca and
cut some laps.....NOT!
  Don Hanson