If you are refering to the disk type spacers, they will move the center of rim off the hub far enough to loose contact with the hub. The trucks weight is suported by the hub, not the wheel studs, so the disk type are a bad idea. The "billet" spacers, like the one pictured above, are also a bad idea becuase they are not hub-centric, meaning the trucks weight is again carryed by the wheel studs. Notice how close to the edge the studs are placed, not enough structural material there for me. There are steel spacers that are hub-centric. they are pricy at about $325.00 a pair.
www.wheeladapters.com I had BS billet adapters on an 86 C10 I had back in the 90s, sold it to a friend of mine. I urged him to put the stock wheels back on the truck becuase I had two adapters break after hitting potholes, well he ignored my advice, the RF adapter broke and sent the truck into a phone pole totaling the truck and banging up my friend pretty good. I agree with Glock, get some wheels with the offset you want, or go with the steel spacers.