April 26, 2018 —

By Larry Mason, www,carsandcompetition.com

Copyright © 2018 Larry Mason


When you watch an Indy car hurtle down the track at speeds that defy logic whether it’s on a street course, road course, short oval or super speedway, the only thing keeping the car on the  track and off the wall is the driver’s ability to control it on four little contact patches created by Firestone Racing Tires. Yes, physics still apply and in some instances the accident that might occur are out of the driver’s control. At the same time, physics, chemistry and mechanical engineering are also the key ingredients in making a safe, reliable and performance-oriented race tire that can see wide extremes in temperature and loading.

I recently sat down with Cara Adams the chief engineer for Bridgestone Americas Motorsports at the Toyota Grand Prix of Long Beach and asked a few questions. Adams is an interesting person not only because she’s a woman in a male-oriented field, but because of the story that got her interested in engineering in the first place. At a very young age her mom had neighborhood science games and her grandfather was an engineer at NASA. He was part of a launch team, and she recently found some fantastic pictures of him from his time working there. That early exposure to science and engineering has stayed with her ever since. She went to school at the University of Akron to pursue her engineering degree. She happened to wander down to the machine shop where they were designing and building a Formula SAE car. “If you talk to most of the engineers here in the paddock, you’ll find that they have Formula SAE experience.” Once she found out about the program, she did whatever she could do to get involved.

Not only that, but her husband gave her tickets to the old CART ChampCar event at Cleveland Burke Lakefront Airport. She was mesmerized for hours. After graduation she looked for a company that had a strong tradition in motorsports and started working for Firestone. She said, “They (Firestone) were on the winning car in 1911 – they’ve got the foundation down. I started in vehicle dynamics group and I moved into racing after a few years.”

Her engineering expertise is in mechanical engineering, tire design, construction, noise and vibration. She relies on “really smart chemical engineers and compounders.” Those engineers work with the tread compound formulations. “There are many different compounds within the tires that aren’t just the tread. They’re brilliant, and they do all their work behind the scenes.”

Street course compounds are the softest in their lineup. The primary (Firestone Blacks) compound is meant to be consistent over the course of the stint. The alternates (Firestone Reds) are designed to be quick at the start and go off as the stint goes on to give the fans something to watch and to give some strategy to the race.

The tire construction varies depending on the track. Street courses have a unique construction compared to permanent road courses which is also unique. All of those are also different left to right. That means a total of eight individual constructions considering the fronts and rears and  side-to-side. Compounding varies between the tracks. For instance a higher speed track like Road America would use a different compound than a tighter track like Barber Motorsports Park or Sonoma, which tends to get a lot of sand on the track which requires a tire with more grip.

Ovals also provide a unique circumstance for construction and compounds. The short oval at Phoenix will be different than Texas or Indianapolis. Tire pressures are much lower on a street/road course compared to an ova, and furthermore, the right side pressure is much higher on an oval due to the increased loading on the outer tires. Firestone also provides for tire stagger (meaning that the right side tires have a slightly larger circumference than the left) on both the front and rear tires on the ovals to help the car rotate into the corner.

For some road courses like Portland or Mid-Ohio where the corners are primarily favoring one direction, the option of measuring the tires to get some extra stagger by swapping left and right sides is a temptation. However, IndyCar rules state that you must run the tires as Firestone has marked. Technically the radial tire sizes for road courses are set at 10 inches wide and 25.8 inches in diameter for the fronts and 14.5 inches wide and 28 inches in diameter for the rear. All are mounted on 15 inch wheels.

IndyCar is key in facilitating an information exchange between Firestone and Dallara (the chassis manufacturer). The tire is essentially a mass spring damper, and therefore plays an integral role in suspension design from Dallara. There was about an 800 pound reduction in downforce on the short oval for this year with the new aero body kit, so the construction has been updated to make sure that the tire foot print can deflect enough to provide good mechanical grip as an integral part of the system That makes the tire a critical part of the overall performance of the vehicle.

Firestone also provides engineers at the track to work with the drivers and teams to make sure that they’re getting the maximum performance from the tires as well as getting feedback to see if they need to change something for next year. The engineers have a sharp eye for detail, and for example found excessive wear on one team’s front tires. The engineer suggested to the team to check the camber setting. The team member said that everything was fine according to his setup sheet. However, with some deeper digging the team found that they had an incorrect steering arm mounted for that track and that therefore caused the excessive wear.

I also spoke with Tom Long from Schmidt Petersen Motorsports during practice, who is a part-time crew member who educated me on the hand-written numbers, arrows and other markings on their mounted tires. He explained that they use a depth gauge to measure every wear hole on the tire as well as a durometer to measure how hard the rubber is across the surface. Arrows are drawn to quickly locate the valve stem and also markings are placed to locate the balance weights. All of these things are checked after the tire has been run on the car to add to the team’s engineering database. To get accurate readings after the tire has been run, a small torch and scraper are used to clean the surface of the tire where the wear holes are to get a more accurate measurement of how much of the tire surface has been used after a specific number of laps. This helps the team with their knowledge base to develop race strategy. Adams said that she’s aware that some teams do this, but that it wouldn’t have a detrimental effect on “heat cycles” of a tire due to the small surface area that they’re working with.

Firestone brought more than 1500 tires to Long Beach for the teams. Each team was allotted seven sets of primary tires, four sets of alternate tires and five sets of rain tires. Since the company’s return to open-wheel racing in 1995, they have logged more than 600,000 tire miles on race tracks including practice, qualifying and races.

So what happens with the massive amount of used tires after a race weekend? Every tire is tracked by bar-code and accounted for so that their proprietary construction and compound techniques don’t get shared with any other manufacturer. Almost every oval tire is cut apart and analyzed to confirm that the tire has performed optimally and some of the road course tires do as well. After that, they get used as fuel for alternative energy.

Firestone has a tradition in winning and engineering expertise. It goes way beyond the simple explanation of round and black!


Photos by Larry Mason


Cara Adams is prepared with notebook and notes in hand for the start of the Grand Prix. She is also prepared to talk to her engineers and staff as well as radio and TV.


The numbers on top are the durometer hardness numbers. The numbers on the bottom show the depth of the wear holes.


The arrow points to the tire valve for an easy way to locate the valve quicker. In racing, time counts for everything!


Here a team member uses a torch and scraping tool to smooth out the tire’s surface in order to get a more accurate reading when he re-measures the wear holes after practice.