leveling blocks

I guess I dont have to say both tires again. As to the blocks, I started with wood and went to plastic. I had to carry 3 ft long and 2 ft and 1 ft to stack them staggered so I could climb them and half the time they would slide apart. I had to buy two sets of plastic and the only real problem I have had is a few times I could not go high enough front to back and one site had blacktop driveways that were surprisingly smooth and I kept pushing one set on the back and it grated some of the plastic on the bottom so they dont want to stack right. I had to trim up the edges and they are OK but not perfect now.