How do 30 pounds of air in your tires hold up 2 tons of car? The next time you get in your car, take a close look at the tires. You will notice that they are not really round. They are squished at the bottom. The flat spot on the bottom where the tire meets the road is called the contact patch. If you were looking up at a car through a glass road, you could measure the size of the contact patch. You would multiply the length of the contact patch by its width to get the area, then...