The Music City Grand Prix last weekend marked the one-year anniversary of incorporating natural rubber derived from the guayule plant into the sidewalls of the series’ alternate tires. Teams use the alternate tires when they need extra speed on road courses and street circuits. Firestone offers the tires with guayule only at its street circuits–St. Petersburg, Long Beach, Detroit, Toronto and Nashville.
Before Firestone debuted the tire made with guayule at Nashville, teams tested it at Sebring International Raceway.
“The feedback from the teams was that it was basically the same tire,” says Firestone Chief Engineer Cara Krstolic. “Josef Newgarden said, ‘It’s not a big deal because I couldn’t tell any difference.’ For us that’s a huge deal.”
At the end of the day, Firestone’s racing division has one primary goal. “We don’t want to sacrifice performance,” Cara says. “We want to have sustainability, but not at the cost of performance or durability.”
Why Find a New Source of Natural Rubber?
The search for new raw materials for tires goes beyond just checking off a hot-topic box for corporate stakeholders. Sustainability provides real-world benefits, and guayule exemplifies that.
First, guayule (aka Parthenium argentatum) is native to the Chihuahuan Desert. Firestone sources its guayule right here in the U.S., in Arizona.
Conventional rubber comes from the Hevea brasiliensis plant. While endemic to the Amazon rainforest, most of the world’s natural rubber comes from Southeast Asia. Being that far away from the U.S. makes it more prone to supply chain disruptions. Also, with the source being closer to where the tires are produced and sold, it could theoretically reduce the cost of tires.
Furthermore, if a blight hit Hevea brasiliensis, it would have catastrophic results. In fact, it was a blight native to South America that helped accelerate the move to commercially produce the plant to Southeast Asia, where that blight is not found.
A bonus to growing guayule is that it requires less water than many crops and can be grown in traditionally less favorable areas for agriculture, such as the desert. Plus, all parts of guayule can produce rubber, from roots up, unlike Hevea brasiliensis.
Why Not Use Guayule Everywhere in the Tire?
Okay, so guayule seems like a solid alternative to traditional natural rubber. Can it go beyond the sidewall?
“Most racing [tire] treads do not contain any natural rubber,” says Cara. “They’re purely synthetic. With a synthetic, you can come up with a lot of different variations [of compounds for different characteristics]. You can tune a tire with different types of synthetic rubber. With any car, [tires] have to be very heat-resistant. If you put a natural rubber in there, your compound is going to start to degrade.”
However, the sidewall still plays an important role in a tire.
“The sidewall is a great place to start because it’s an important characteristic of the tire,” Cara says. “It protects the carcass, the body of the tire. It has heat mitigation properties. It’s also in one of the more safe areas of the tire, and we can take what we learned from there and apply it to other areas of the tire.”
As far as the tread, Firestone might have found a more sustainable source for its materials.
Look no further than what’s probably in your kitchen now. You know, those plastic bags that pile up because you seem to always forget to bring reusable bags when you go shopping. Well, don’t feel as guilty about that.
In partnership with Shell, Firestone incorporated butadiene1 into the tires used for the 2023 Indianapolis 500. Butadiene1 is a monomer produced from hard-to-recycle used plastic that you find in shopping bags, stretch wrap and other flexible polymer packaging.
Why Experiment With New Materials in IndyCar?
Racing provides the perfect medium to test tires, according to Cara.
“In any form of motorsport, you are always pushing limits,” says Cara. “At Bridgestone [Firestone’s parent company], we are redefining limits. When we test tires, even before they get to the race track, we look at them, dissect them, run them on high-speed tests that go well above where we would run them on the race track. The reason we do that is that we want to challenge [the tires].”
There’s also another reason that motorsports serves as a place to experiment with new technologies.
“The wonderful opportunity we have in racing is we can use small quantities,” Cara says. “If you have a regular production tire [for the street], if you go to one of those plants, they’re maybe making 30,000 tires a day. We make 30,000 tires a year [for racing]. We can have a big impact with a small volume in motorsports.”
What Does the Future Look Like?
Firestone Chief Engineer Cara Krstolic with a race tire using materials derived from guayule. Photo by J.A. Ackley
When can you expect guayule in race tires for tracks other than the street circuits?
“The quantity and scale-up is something we’re working on right now,” says Cara. “Right now, we have enough material for street courses. In the future we would do road courses and then ovals.”
The race for alternative materials to make tires is on, and that includes those for racing.
“By 2050, the company announced that we will have 100% renewable or circular materials in our tires,” Cara says. “This will include the entire portfolio [including race tires]. To get to where you’re 100% sustainable, you have to start making steps.”
For Cara Krstolic, a former Formula SAE participant, the quest to develop a sustainable race tire is a personal one, as it is for many others at Firestone.
“Most of us in IndyCar grew up racing our own cars, building cars or [being involved in] anything automotive,” says Cara. “We love racing. We want to make sure [racing] is around for a long time. The only way we’re going to be able to do that is to make sure we do it sustainably.”