Tires are among the most environmentally problematic parts on any vehicle.
Besides being made primarily of synthetic rubber made from petroleum-derived products, the natural rubber content in virtually all tires comes from tropical sources in South America, Africa, and Southeast Asia, where the Hevea or Pará rubber trees are grown.
Because these trees require a tropical or subtropical climate with a minimum of about 47 inches per year of rainfall and no frost, rubber production contributes to deforestation in the Amazon basin and around the world.
About 40% of every tire on the road today is made of natural latex rubber, but Bridgestone Americas is working to develop a more robust and environmentally friendly source of latex that can be grown in the U.S. The source is a plant called Guayule.
“Guayule is a shrub that’s been around a very long time,” said Cara Krstolic, chief race tire engineer at Firestone Tires, a division of Bridgestone. “The shrub has a lot of natural rubber in it. So the roots, the stems, the leaves, all have latex in them.”
Simply a good idea
Krstolic told TheDetroitBureau.com developing Guayule has multiple benefits.
“In addition to tires, we rely on natural rubber for things like surgical gloves and instrumentation,” she says. “If you’re relying on one species or one genus of tree and there’s some kind of fungus or blight that takes out the tree, it could take out the natural rubber supply for the whole world.”
Future-proofing its supply chain would be reason enough for Bridgestone to look for alternatives, but there are other benefits in play.
“To diversify our supply and to have a domestic source of latex, we’ve spent about $100 million investment in research on Guayule,” Krstolic said. “We’re growing it right now in Arizona. The other great thing about the Guayule plant is that it doesn’t use a lot of water.
“If you compare it to some of the other crops that are being grown in these areas like cotton or alfalfa, it uses about 50% of the water that those crops require. So some of these areas that are affected by climate change, increasing temperatures, or drought in general, they are able to grow this crop more easily than those other crops.”
When the product is fully developed, Guayule-derived rubber will be a direct replacement for natural rubber currently sourced from the Brazilian rainforest.
“We’re just looking at the latex in its pure form, and it should be identical,” Krstolic said. “As long as we process it the same way and treat it the same way, it should act the same way in the tire. That’s the beauty of looking at just the chemical structure. When it comes right down to it, you can get the same type of performance and the same type of tire as you would get from the Hevea tree.”
Major investments in R&D
Bridgestone plans to invest an additional $42 million to establish commercial operations, with additional investment and expansion planned toward 2030. The company will collaborate and partner with local U.S. farmers and Native American tribes to increase capacity of up to 25,000 additional acres of farmland for planting and harvesting guayule at scale.
An additional benefit, the crop can be farmed with existing row-crop equipment, helping to save costs for farmers. Bridgestone is targeting sustainable commercial production of Guayule-derived natural rubber by the end of the decade.
“We’re extremely bullish on the potential for Guayule as a domestic source of strategically critical materials, such as rubber, hypoallergenic latex, building material adhesives and renewable fuels, just to name a few,” said Nizar Trigui, chief technology officer and group president of solutions businesses for Bridgestone Americas.
“With Guayule, we can reduce the environmental impacts that come with overseas sourcing while also realizing a more sustainable agricultural system for parts of this country that are facing persistent and worsening climate conditions, so it’s really something with many benefits for our environment and our economy.”
Bridgestone has also received multiple U.S. government grants for Guayule research and development, including from the U.S. Department of Agriculture in 2017 and from the U.S. Department of Energy Joint Genome Institute in 2021.
Tested on the race track
Bridgestone Americas turned to its Firestone racing tires division to test Guayule-derived rubber under the most exacting conditions in the IndyCar racing series. When IndyCar races on a street or road course, fans may notice that some of the tires have a red sidewall. That indicates the driver is using the “alternate” tire compound.
Firestone alternate tires have a softer rubber compound than primary tires, allowing for faster speeds and better cornering, but at the expense of faster wear. Each team receives a limited number of alternate tires to use strategically during a race weekend.
Firestone Firehawk racing tires made with Arizona-grown Guayule natural rubber were introduced at the Indy 500 Pit Stop Challenge in May 2022. The green-sidewall tires were the first look before making a full competition debut as the red-sidewall alternate race tire at IndyCar’s Big Machine Music City Grand Prix in Nashville in August.
“We want racing to be the ultimate proof point for our technology,” Krstolic noted. “IndyCar is one of the most versatile and demanding motorsports series in the world because they run on street courses, road courses, and ovals, so these tires face really grueling conditions. If we at Firestone can put new technology in the tires that see these conditions on the racetrack, then we can transfer that technology into street tires. That’s our ultimate goal.”
Bridgestone plans to incorporate Guayule rubber into more of its race tires in 2023.
Guayule rubber in your street tires
Currently, Bridgestone is expanding the number of local farmers growing Guayule in Central Arizona, and it is targeting 350 new acres of Guayule to be planted in 2023. The conversion to less water-intensive crops is a direct result of Bridgestone’s agreement with the Environmental Defense Fund, a nongovernmental organization actively involved in water shortage solutions for the Colorado River, which is used for irrigation in Central Arizona.
“The challenge with Guayule is the scale-up process,” Krstolic said. “That’s where we’ve put so much effort and investment; to make sure we can maximize that plant through selective breeding and come up with the most rubber and the easiest process. Now we’re in the commercialization phase. We’ll be building some street tires, and we hope to have this in a lot more tires by the end of the decade.”