Scions-
Not to beat a dead horse, I apologize for the length but I offer the
following for clarification. Some of this has already been
discussed...................
Camber-The inward or outward tilt of the wheels from true vertical as viewed
from the front or rear of the vehicle. The vehicle will always pull to the
side with the most negative camber.
Castor- The forward or rearward tilt of the steering axis in reference to a
vertical line as viewed from the side of the vehicle. Castor will also cause a
pulling condition; it will always pull to the side with the least positive
castor. Castor is used as a stability angle to assist the steering wheel to
return to center. The more positive the angle, the more stable the vehicle
will be. Negative castor will cause a wandering or unstable condition at the
steering wheel. Castor does not cause premature tire wear.
Toe- The difference in distance between the front and the rear of the tires.
Toe is the biggest contributor to tire wear. Any adjustment to camber or
castor will affect the toe. Excessive toe-in results in an over sensitive
steering wheel. Excessive toe-out will lack a sense of control or direction.
SAI (Steering axis inclination)-The angle formed between true vertical and an
imaginary line drawn between the upper and lower pivot points of the spindle.
Included angle- SAI added to the camber reading at the front wheels. It is
determined by the design of the steering knuckle or strut. It is not
adjustable.
TOOT- (Toe Out On Turns)- When turning a corner, the inside wheel has to turn
at a sharper angle than the outside wheel because the inside has a shorter
distance to travel.
Thrustline- A line which bisects the rear toe, or the direction the rear
wheels are pointed. If the rear wheels are pointed to the left, then the
thrustline will be left. Thrustangle can be calculated by comparing the
thrustline to the geometric center line of the vehicle.
Setback- The measurement of the wheelbase on each side of the vehicle after
the alignment is complete.
With the TR6 IRS the rear toe and camber can be adjusted. This can result in a
thrust angle change as well. I am not sure about the Spitty/Herald setup but I
would guess it is has the same adjustment capabilities. Camber and castor
(when adjustable) usually work in conjunction with each other. IE: one affects
the other. Here in Maine, due to the road crowns that we have, the camber
and/or the castor are adjusted to compensate for the road crowns and this will
result in a vehicle that does _not_ pull to the ditch. Usually it will only be
1/2 degree or so from one side to the other. YMMV
Hope this helps......
Tim Hutchisen
71 TR6
80 TR7 Spider
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