The Maximum Motorsports Panhard Bar eliminates the Mustang's unstable and unpredictable behavior while cornering near its limit. This feeling is caused by the rear of the car steering itself without any input from the driver. Rear end steering is caused by the sideways movement of the rear axle. In addition, the Mustang upper control arms are at about a 45 degree angle from the direction of the cornering load. Some binding in these arms is induced during cornering as one arm enters into compression and the other enters into tension. Do NOT use urethane in the upper arms to improve the side to side motion of the axle. Because of the three dimensional movement of the upper arms, severe binding will be induced as the suspension moves--with or without a Panhard bar. This effect may not be evident in a drag-only car, but if you plan to drive the car on the street at all, we do not recommend urethane in the upper arms.