Re: Wandering, Negative Steering Roll Radius?

[Luis Marques <marques@ti.com>]

  "NSRR places each front wheels pivot point outside the center of the
   tires axis. This has the effect of making the front wheels want to
   return to center-to turn in the direction opposite that of the
   pivoting force-even under conditions when one front tire has far
   better traction than the other. When this happens on a conventional
   automobile, as when the driver must brake hard in a corner, has a
   blow-out, or has one front wheel drop off the road, the front tire
   that retains traction has greater stopping power."

So, basically, when you have one front tire braking harder than the
other, the tire with better braking is forced to turn opposite to the
yaw introduced by unbalanced braking forces.  This is very good for
directional stability when making hard stops, or a tire blows out, etc,
but I don't see how it helps straight-line stability under normal
driving, since you just have a little engine power trying to force an
equal amount of toe out on each wheel against the wind resistance (since
power is slit 50/50).

I would think that the same "negative radius" feature is designed on the
caster plane.  Having the front wheels centered behind the pivot point
will probably make the car's own weight force them to point straight
ahead.  Now that I think about it, this should be more effective in
curing the wandering of wider tires than having more offset on the
wheels.  It is well know that if you increase the caster, you improve
high-speed stability (at the expense of increased steering effort), just
like the fork offset in bicycles.  For a car with McPherson struts, this
could be achieved by moving the strut bearings back a little.  Not easy
to do on a 4kq, but perhaps easier to do on a 5000/200 etc.

Luis Marques
'87 4kcsq