This was the part that surprised me the most: "Passenger car tires need to have 10-40 percent natural rubber content to allow them to stay flexible at low temp

This was the part that surprised me the most: "Passenger car tires need to have 10-40 percent natural rubber content to allow them to stay flexible at low temperatures and to keep tiny cracks from growing. Truck and aircraft tires need an even higher percentage." I had always assumed that modern tires were completely synthetic. Very interesting.