The average car tire runs from 24 to 28 inches in diameter. Light truck tires as on a 4 wheel drive or pick up run around 27 to 33 inches diameter. A typical width falls from 6 to 8 inches across the sidewalls when mounted and inflated. Medium and heavy duty truck tires are obviously much bigger. Not far from here is a small power plant that shreds scrap tires into fuel pellets. They only sort the incoming carcases by whether or not they have steel belts because they require additional processsing before using as fuel. Otherwise their incoming tire scrap piles have a variety of sizes. Just something to keep in mind when building a 'prototypical' scrap tire pile, they're not all the same size.
Back to the original question, construct a large bin or fenced enclosure and use foam or other filler and then add enough tires to create the illusion of a large pile without exposing the filler.
