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INTRODUCTION

REDUNDANCY

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STEERING

WEIGHT

MISCELLANEOUS

SUV STABILITY

DIALOG

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STEERING SYSTEM TRIM

Try this test.

  • 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

  • Dragging brakes and other mechanical defects

  • 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.

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