For 1990-2009 cars

Steering Axis Inclination (SAI) is the inward tilt from the vertical at the top of the steering axis. The inclination angle is the angle between true vertical and a line passing through the center of the upper mount and the lower ball joint, as viewed from the front of the vehicle. SAI helps the vehicle track straight down the road and assists the wheel back into the straight ahead position. SAI on front-wheel-drive vehicles should be negative.