Re: Los Angeles robot traffic ticket and Caster

[bearbvd@domain.elided (Greg Hermann)]

At 4:10 PM 12/7/99, David Bongiovanni wrote:
>The fuzz is playing the same game here in San Francisco.  I've noticed
>that the photo radar intersections have yellow lights that last about
>half as long as the intersections nearby.  Aren't these photo radar
>installations subcontracted to commercial operations who make a
>commission on every ticket?  Sounds like the big scam to me.
>
>If you want true automotive freedom, try http://www.nasaproracing.com,
>you can't beat it at $150/day for road racing and open track.
>
>As far as caster goes, most modern automobiles require positive caster,
>meaning the centerline of the kingpin axis is farther back at the top.
>Too little positive caster places the tire contact patch in front of
>the  steering axis, causing the front tires to be unstable when tracking
>straight ahead.  A car with too little positive caster will run right
>off the road if you let go of the wheel, but will turn in better,
>understeer less, and have light steering a low speed.  Too much positive
>caster will cause heavy steering at low speed, understeer, possibly
>vagueness on-center in the steering, and good directional stability.
>I've found that the stock settings for caster and toe on my GTV6 provide
>the best balance of the above mentions characteristics, though the
>negative camber really needs to be increased to maximize tire
>performance.

Caster , according to the truly proper definition, is the fore and aft
distance from the center of the tire contact patch to the point where the
(extended) centerline of the (now imaginary) kingpin axis intersects the
pavement. Positve caster is defined as when the axis intersection falls
ahead of the center of the contact patch, and negative is the opposite.

Steering self-centering effect, directional stability, turn -in feel, and
the like are affected primarily by CASTER.

Caster ANGLE is the fore and aft inclination of the kingpin axis.

Kingpin inclination is the side to side inclination of the kingpin axis.
(Angle in the same pl;ane as camber, but NOT to be confused therewith).

The difference between the kingpin inclination angle and the camber angle
is determined by the design of the knuckle and spindle.

A caster angle LESS than the kingpin inclination angle will give an
increase in positive camber on the outside wheel as a car is steered into a
turn, giving a tendency toward understeer. (And, vice versa.)

The relationship between caster and caster angle is determined, once again,
by the design of the steering knuckle and the spindle.

The only things we really are left to play with are wheel offset, caster
angle, and knuckle risers.

A car with wheels which leave zero lateral offset between the tire contact
patch and the intersection of the king pin axis with the ground, but which
has a small amount of positive CASTER when the CASTER ANGLE is set to be
slightly LARGER than the kingpin inclination will have near ideal steeering
response characteristics. The steering will be a wee touch heavy--because
the nature of this kind of geometry is to LIFT the car up slightly when the
wheels are turned! But this is a LOT less effect than one gets from too
much positive wheel offset.

Greg
>
>--
>David Bongiovanni
>84 gtv6
>87 graduate
>75 rabbit neuspeed gti-cup

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