ROADMASTER ACTIVE SUSPENSION #4618-A FITS: 07-12 TOYOTA TUNDRA # MK4-XXDDHA This is a full active suspension kit - only one required per vehicle. It comes assembled and ready to install. U-Bolts only need to be removed on the MK2 models - MK3 and MK4 do not require removal. Unlike stiff air shocks, active suspension only stiffens the ride while towing, retaining the normal smooth vehicle ride when not towing. Made in the U.S.A. See additional application information: http://www.activesuspension.com/images/stories/pdf/appguide.pdf