Fabtech 07-15 GM 1500 4in Front Dirt Logic 2.5 Reservoir Coilovers - PairDirt Logic 2. 5 Resi Coilovers. From our desert racing experience the Dirt Logic 2. 5 has been developed for exceptional performance in a variety of Coilover applications. The Dirt Logic 2. 5 will provide incredible dampening capacity for aggressive offroad driving. Features: 2. 5in OD Stainless Steel Body. 2. 25in OD Billet Aluminum Piston. 7 8in NitroSteel Black Piston Rod. Cold Wound Coil Springs. Adjustable Coilover Construction. 5 8in Spherical