Actually, the manufacturers COMPLETELY control the design of tires. Not on the drawing board, but with the contracts they hold out. Tire technology is as good as it gets. But what the manufacturers buy is almost never top quality stuff. Manufacturer of BrandX Trucks goes to Tire Company Z and says "I want a light truck tire for my new line of trucks. It has to do light offroad use, have good highway handling, deal with all kinds of weather, hold up for so many minutes if it goes flat, to meet federal guidelines, blah blah blah." Tire company Z says "We already have a tire that does all that, here it is. The AllterrainZ. It costs $."
Problem is, BrandX Trucks wont pay $. They pay PEANUTS.
Tire companies are hurting bad these days. Demand is down. Technology has increased to the point where productivity is at an all time high. So is quality. They dont have to throw away as many because fewer fail the quality tests. They can make more in less time than ever in history. But they also last longer, so secondary tire sales have dropped. Sales of new cars are down, so they need fewer tires for new car production. Every contract is necessary to stay alive. So when the BrandX Truck Co. says "We will give you a contract, but only if you can make the tires for this amount instead of what you want," they have to find a way to cut corners. So instead of the high quality tires you COULD get, the high quality tires that are stacked in rows and rows in a warehouse at Tire Co. Z's facility, your new vehicle gets the crap tires that BrandX was willing to pay for.
This happens every day. Its not limited to Explorers, its not limited to Firestone Wilderness AT's, its not limited to any one company or any one brand of tire from that company. Every design made for manufacturers of new cars these days is a gamble waiting to roll snake-eyes. Firestone just cut the wrong corner, and the nightmare all the tire companies were waiting for happened. Luckily for the Auto makers, Firestone played the game afterwards and didnt blow the whistle on the whole shebang. That would have KILLED new car sales if people believed it. Then NOBODY sells tires. Nice thoughts huh?