Behind the Scenes of Tire Design

July 9, 2012 12:29 AM
Behind the Scenes of Tire Design

Firestone ag tires are engineered at a state-of-the-art technical center and tested at a historical farm.

There are more than 30 compounds, months of engineering and testing and a whole lot of history in every Firestone ag tire. Going back to the company’s roots, every Firestone ag tire is tested on the historical farm of Harvey Firestone, who first put pneumatic tires on tractors 80 years ago.

The 400-acre property in Columbiana, Ohio was deeded to the Firestone family by President Thomas Jefferson. The farm once hosted gentlemen’s camp outs with Firestone, Henry Ford and Thomas Edison in attendance. The property was established as the Firestone Test Center in 1952, and the grounds are used for testing as well as leased to a local farmer for production.


Today, many of the tests are head-to-head comparisons of new Firestone tires vs. the previous design as well as new Firestone tires vs. the competition. With the facilities, Firestone test engineers can simulate four years of wear and use in three months.

The tests are run 12 months a year on the indoor equipment as well as the five circles with concrete, black top and limestone surfaces. The test circles are the site for wear and durability tests, and the test tractors are run without an operator. The equipment is mounted with the tires for testing, the steering is locked in position, and using a remote start the tractor takes off in its circle pattern and run for 48 hours in one direction before the equipment is stopped and the direction of travel is reversed. For safety, the tractor is tethered to a concrete post and there is monitoring equipment at each tire and on the tractor so that if something malfunctions, the engine is immediately stopped.

For more hands-on, extreme testing, the crew calls on the Mean Machine, a custom-made vehicle developed in the 1975 that has up to 32,000 lb of drawbar pull. It’s a unique Detroit Diesel engine-powered machine designed to provide drag for wheel slip tests on the tractor pulling it, and its tires are filled with beet juice, but were once filled with calcium chloride.

Another unique machine at the test farm is a ¼ scale machine used for the early screening of tire compounds. Specially prepared tires are run over a variety of surfaces to simulate different field wear conditions. Currently the testing for this machine is being focused on developing a more stubble-resistant tire surface.

In addition to those tests, the crew can run vibration pad testing to simulate furrow or hillside driving, and with its 400 acres, the team can conduct field tests.

Every tested tire is analyzed for performance. TekScan is a technology that produces an electronic footprint image to display pressure exerted by the tire. To test sidewall strain, a tire sidewall is prepped and a laser system is used to measure hot spots on the tire sidewall. A proprietary technology to Firestone is its 3D tire profile, which can be utilized on new and worn tires to provide a three dimensional profile of the tire. Upon conclusion of testing, a tire is cut and dissected. All data and tire sections are delivered to the engineers in Akron.

Where It Begins.

The test center is the final step in the development of Firestone ag tires. The process begins at Bridgestone’s Americas Technical Center in Akron, Ohio, which is one of three of its kind for the company with the other two located in are in Tokyo, Japan and Rome, Italy.

The brand-new Akron facility was opened in April 2012 and employs 450 Firestone engineers, lab technicians and scientists. The $100-million building is certified to Leadership in Energy and Environmental Design (LEED) Gold standards, and many of the products used were from the company’s Firestone Building Products division.

The building houses chemistry and physical property labs that focus on all aspects of tire development. In all there are more than 30 compounds in an agricultural tire, whereas only 20 in a passenger tire.

The high-tech facilities include a 3-dimensional printer that can produce a 10"x10"x8" sample of a prototype tread, for example. Another lab is outfitted with four tensile and test robots, which replaces a hand-operated process, and the robots can cycle 18,000 samples a month. Those machines are being used in the development to calibrate tires against stubble damage.

In the ag division, eight engineers are dedicated to developing the Firestone ag tire lineup.
"We have a dedicated engineering team to agriculture, and our tires span from 20" to 91" outer diameter tires," says Firestone Ag President Ken Allen.

Using computer programs, engineers can virtually build and test tires beginning with the baseline standards and then adding factors such as size, load, inflation pressures and wear requirements.
"With our computer systems, we can run multiple cycles in a tire’s development to optimize its performance," says Ben Rethmel, Firestone engineer. "Everything can be designed by the computer—body plys, the number and length of belts, compounds used and the tire’s shape.

After its design is completed, the virtual tire can be put in environments for simulated stress and strain.

"We can generate multiple views of the tire static, in motion, or under load," says Brad Harris, Firestone engineer. "Then we can apply lugs and design those for best traction."

Using a program originally development by a Bridgestone (Firestone’s parent company) business unit for snow traction, the ag engineers use CROSS, which is a program that simulates soil conditions in the field. To develop CROSS for ag applications, the team had soil samples pulled from across the Midwest ranging from muck to sand. Those parameters were loaded into the program which can now simulate those soil conditions for the virtually developed tire.

"All of the computer engineering speeds up the process of new tire development and saves a lot of money because adjustments can be made before a mold is ever created," Harris says. "Our goal is to have the testing at Columbiana only confirm our virtual work and not demand adjustments."

What’s Ahead.

The engineering process is layered with evolving challenges.

Tires are becoming larger in response to carrying heavier loads at lower pressures. The trend has been for tire sizes to go up in group size to make more room for air. But that doesn’t mean every tire is available in every size.

"The difference in today’s tire market is that we don’t make one tire in every size," says Allen. "A top issue is the application-specific tires for grain carts and sprayers. These demand lower soil compaction, and lower contact pressure, but still carry the load and have traction."

The general rule of thumb for matching group size to horsepower is: Group 47 for 200 hp; Group 48 for 300 hp; Group 49 for four-wheel-drive models; Group 50 for 600 to 700 hp and larger four-wheel-drive models.

Producing larger tires in higher quantities was reaching the limits of tire production—larger tires take higher pressures and longer times to cure at the factory. In response, Bridgestone will invest $74 million to expand capacity at its Des Moines, Iowa factory. This is following a $77 million investment announced in March 2010. The Des Moines factory is the company’s primary agricultural tire manufacturing facility that employs 1,673 people. The improvements as a result of the total $151 million expansions are planned to be completed by 2013.

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