Overload spring installation kit.... not tires!. Installed on a 90's chevy 1 ton truck. Fairly easy to do. Good instructions with pictures. Wish the u - bolts were better quality needed to chase the threads with a tap so nuts would go on properly on 2 of the u bolts. But that's not the sellers fault. With clean threads goes together easy with only 1 person. All in all a very good product.