Try this test.
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Steer your vehicle straight ahead on
level, straight road
-
Relax your grip on the wheel so it is free
to turn, but guard the wheel
-
Note if your car keeps going straight more
than a second or two or whether it tends to "lead"
Most cars tend to pull; some a little, some a
lot. Most lead to the right; but, some will go left. Lead to the left is
considered dangerous.
Unquestionably, it is most desirable that a
car want to continue going straight ahead unless driver input turns it. Wheel
alignment is perhaps the most important factor in controlling lead, but not
the only one. It is the other variables which make it virtually impossible for
any fixed alignment to neutralize leading tendencies. The factory alignment
specs only provide a manufacturing or field tolerance for approximately
correct alignment angles which yield tolerable results on most roads. If your
car leads after an alignment which restores factory tolerances, then your car
is deficient in that it needs a steering system trim control, an auxiliary
control system to be built in to the suspension system to allow the driver to
make small adjustments as will be detailed shortly.
Having to compensate for lead really
increases driver load and adds to fatigue, especially on long drives. I
consider it a safety hazard.
No amount of complaining to the alignment
shop will do you any good because the perfect alignment is not doable with
today's vehicles. This is because the required alignment angles for neutrality
are dependent on several factors:
-
Caster and camber angle
-
Tire variation, inflation, and wear
-
Road camber
-
Cross winds
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Dragging brakes and other mechanical
defects
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Uneven loading and resultant suspension
angle changes
With all these variables what can be done to
solve this problem of lead. The solution is quite obvious. A trim control is
needed.
Aircraft have used trim control almost since
the beginning of aviation. Trim on aircraft takes the form of small movable
surfaces or trim tabs on primary control surfaces which alter the airflow such
that that small changes in pitch, yaw and roll can be made to the aircraft so
that it flies straight and level. As weight and balance or atmospherics
change, the pilot can dial in more or less trim to keep his craft on a even
keel.
The analogy already exists in cars in the
form of a speed control (cruise control). But this topic deals with the
here-to-fore previously unaddressed problem of directional stability. I
believe that the problem of lead can be solved with the design of a steering
trim control, whereby the driver literally realigns his
front
wheels as he drives. From the driver's point of view, the control would take the form
of an annular ring below the regular steering wheel. With the car on a
straight road, the driver would relax his grip on the steering wheel and
ascertain if lead was present and if so, in which direction. He would then
correct the lead by turning the annular control ring either left or right to
compensate. As he turned this trim control, a motor would be actuated which
would then turn a jackscrew in the suspension system. This jackscrew would
then change the camber angles of the two front wheels in equal and opposite
directions up to a maximum of 1 degree. This is a very small amount, but quite
enough. Wheel camber geometry is illustrated at left. The driver would sense the exact moment of neutrality where all lead
is eliminated. It is similar to tuning a conventional radio dial. The station
just pops into tune. Well, the car would do the same, with the sweet spot of
neutrality relieving the driver of the burden of constant counter-steering to
maintain direction.
I see this as an option on luxury cars
initially, with it becoming standard equipment over time.