To run a 285 or larger tire on the factory wheels of your 2007-2020 GM Silverado / Sierra 1500 6-lug new body style pickup you may need to use ReadyLIFT's 15-3485 1/2" front wheel spacer. This spacer is essential as factory wheel options and backspacing differ. This lift kit known as the 66-3085 ensures that your factory springs are not compressed and does not require cutting the strut studs. Importantly it will not affect your factory OEM ride quality or comfort level. The 66-3085 kit includes two Aluminum SST Strut Extensions and two Aluminum SST Lower Strut Mount Spacers all constructed from CNC-machined 6061-T6 solid billet Aluminum. This high-quality construction ensures durability compared to cheaper kits made from low-grade stamped steel. Please note that this kit is compatible with new 2015-2020 GM 1500 Trucks. However if your truck is a 2017 model with stamped steel upper control arms it may require either aftermarket upper control arms or the purchase of Aluminum factory upper control arms. Stamped steel control arms on 2017 models are known to have issues with ball-joints when leveling or lifting the suspension. To determine the proper fitment of the leveling kit use a plumb bob line to measure from the center of the wheel hub to the bottom edge of the fender at the 12 o'clock position while the wheels are pointing straight forward. If this measurement is greater than 22 inches it means your truck already has some factory or aftermarket front lift compared to a base truck. For distances measuring greater than 22 inches #66-3086 or #66-3085 should be modified to account for the pre-installed lift. Incorrectly using these kits on a truck with 22 inches or more distance may result in component interference and excessive wear. Additionally some vehicles may require the use of 1/2" front wheel spacers when using aftermarket tires on certain factory wheels but the factory wheel options and backspacing can vary.