Upper A-Arms

When the Toyota FJ Cruiser is lifted the front geometry is change so the Castor can no longer be set to factory specifications. The FJ will feel light on the road and will tend to wander more than normal. To fix this issue there are a number of vendors that are producing aftermarket Upper A-Arms that change the geometry so the Castor can again be brought back into factory specifications. Many of the aftermarket A-Arms are also beefier and include grease zerks for maintenance.

About Castor:

Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it’s tilted forward, then the caster is negative.

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as “trail.”


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