The U.S. Army needed millions of tires for its trucks and other vehicles. Rubber was also used to manufacture tanks and planes. But when Japan invaded Southeast Asia, the U.S. was cut off from one of its chief sources of this critical raw product.
What's more, new speed limits and gas rationing forced people to limit their driving, helping reduce wear and tear on tires. A synthetic rubber industry was created. The public also carpooled and contributed rubber scrap for recycling.
Source: The National World War II Museum