the SLA or Short Long Arm suspension on an Explorer is why you get more negative caster when lifting the front with the TT,
as the arms pivot , the lower arm being longer than the shorter upper arm has a a narrower arc , as opposed to the short upper arm that has a a wider arc,
from Wiki,
A short long arms suspension (SLA) is also known as an unequal length double wishbone suspension. The upper arm is typically an A-arm, and is shorter than the lower link, which is an A-arm or an L-arm, or sometimes a pair of tension/compression arms. In the latter case the suspension can be called a multi-link, or dual ball joint suspension.
The four-bar link mechanism formed by the unequal arm lengths causes a change in the camber of the vehicle as it rolls, which helps to keep the contact patch square on the ground, increasing the ultimate cornering capacity of the vehicle. It also reduces the wear of the outer edge of the tire.
SLAs can be classified as short spindle, in which the upper ball joint on the spindle is inside the wheel, or long spindle, in which the spindle tucks around the tire and the upper ball joint sits above the tire.
[edit] Disadvantages
Short spindle SLAs tend to require stiffer bushings at the body, as the braking and cornering forces are higher. Also they tend to have poorer kingpin geometry, due to the difficulty of packaging the upper ball joint and the brakes inside the wheel.
Long spindle SLAs tend to have better kingpin geometry, but the proximity of the spindle to the tire restricts fitting oversized tires, or snowchains. The location of the upper balljoint may have styling implications in the design of the sheetmetal above it.
SLAs require some care when setting up their Bump Steer characteristic, as it is easy to end up with excessive, or curved, bump steer curves.
