TECH TIP: For 'bag placement, we need to know two important measurements: half of the overall tire diameter and wheel center when the truck is laid out. A fully deflated 'bag is 3 inches plus a 1/4-inch safety. So, to set up our truck to run 18s, we bolted the top of the 'bag plate on the 'bag, jacked up the truck, and set the 'bag between the frame and the lower control arm to know how much room we needed to lay out completely. Then we can measure wheel center on the hub to ensure we're laying out with our desired wheel/tire combo. See steps 15-17.