This is the Pro-Line ProTrac Rear Suspension Arm Set, and is intended for use with the Pro-Line ProTrac Suspension Kit for the Traxxas Slash Short Course Truck. Pro-Line's new ProTrac™ Suspension kit for Slash® is one easy to install kit that greatly increases forward acceleration, corner speed, consistency and drivability. The critics are ranting and raving about ProTrac™. RC Car Action Magazine: "It all comes down to the numbers. According to the stopwatch, my laps were about 1 ½ to 2 seconds faster with the Pro-Line suspension system.” Xtreme R/C Car Magazine: “The result is almost staggering after my test down at OCRC Raceway. We can’t recommend this kit enough.” Why ProTrac™ ? Faster, more consistent laps Increased Forward Acceleration More Fluid Suspension Geometry for Jumping Light Weight/Race Inspired Design Increased Tunability Double Jump Durability One Easy to Install Kit What’s included: (2) Rear Arms (2) Rear Arms