Zone Off-road doesn't design just spacer kits, we design suspension systems. To maximize performance, a lot of testing was done to ensure the correct durometer material was used to maximize vibration absorption and absorb harsh impacts while ensuring they are tough enough to last the life of your vehicle. In addition to using the perfect durometer material, a UV stabilizer was added to ensure the material wouldn't break down over time. After the perfect spacer was created, Zone Off-road didn't forget about the bump stops. Many companies sell just the spacers without including bump stops or bump stop extensions. The factory coil spring was never designed to collapse farther than the factory wheel travel, so not installing extended bump stops may drastically reduce the life of your factory coil springs. Zone Off-road bump stop extensions can handle any impact that you can handle while driving it. We know this for a fact!