I started out by baking two 14" cakes, since I wanted to make sure there was plenty of cake for the party. I leveled, torted, filled and stacked the cakes. Then took a bread knife and started cutting away on the outside of the cake to make a tire shape. I then attacked the center (with a smaller knife) to cut out the middle.
Then I frosted the cake with whipped buttercream, and rolled out black fondant to cover it with. Covering a cake (with a hole in it!) with fondant is no easy feat. I finished putting the fondant on and smoothing it, only to see it starting to rip in the center where the hole was. So, I took an exacto knife and made slits in the fondant so it was lay flat along the inside of the tire. I figured I'd find something to cover it with later. I then took a dogbone gumpaste tool and made tire tread marks on the sides of the cake, as a tire has. I looked at the pictures I had of John Deere tires, and they have a yellow center to them. Perfect!! I rolled out some yellow fondant, cut a circle put it on the inside, covering up my ripping black fondant. I also piped a star edge around the yellow to neaten it up.
I had also purchased some John Deere hot wheels-type cars to put on the cake, since the birthday boy wanted a construction site. He described the construction site as "having lots of dirt and rocks", so that's what he got! The piles of dirt are mounds of frosting covered in home-made "dirt" (graham cracker, brown sugar, white sugar, pepper, nilla wafers and cocoa powder all ground up). The rocks are chocolate rocks I bought somewhere (no idea where, lol). I used piping gel to get the rocks to stay in the trucks, and frosting for the piles of dirt in the trucks.
Here's a close up of the trucks:
The birthday boy was extremely happy with his cake!