Doug Siefkes for Cooper Tires
Developing tire compounds is like baking bread. Mix together a few key ingredients and you’ve got the basic recipe. Flour, water, yeast and sugar in the right amount and order will produce your basic bread. Add in some extras, like sweeteners, seeds and butter, and you will create changes in taste and texture.
Commercial truck tires have basic ingredients too. It all starts with a mixture of mostly natural rubber and/or some synthetic rubber, filler materials (typically carbon black and silica), waxes and oils as well as various chemical additives that promote elasticity, eco-friendliness and durability. If rubber were not mixed with an additive like carbon black, a sooty by-product of the burning of oil that gives tires their blackness, a tire’s tread would be too soft and have no resistance to abrasion.
Silica, a basic component of ordinary beach sand, is traditionally used to enhance cut/chip/chunk resistance. Tire engineers discovered in the 1970s that rolling resistance could be reduced, and durability increased, by replacing some of the carbon black with reacted silica in light tread vehicles’ tires. But there was a trade-off, especially when combined with natural rubber tread compounds in commercial tires — the lower rolling resistance could potentially affect abrasion and wear resistance.
Today, compounding engineers at Cooper work to develop the optimum mixture of ingredients that will create the perfect functionality for a particular application.
According to Phil Mosier, Cooper Tire’s manager of commercial tire development, “unpeel” a commercial tire and you’ll find 12 to 15 different compounds can go into one tire. There’s the tread compound, which is going to have contact with the road surface; underneath that is the base compound to help dissipate heat; other compounds go into the wire belt and the sidewalls of the tire. Because of the necessity for flexibility, tear and crack resistance in the sidewalls, Mosier said that tires will often consist of a combination of natural and synthetic rubber compounds specially engineered to meet those requirements.
“Developing the compound formulations to achieve the desired balance of performance properties is a delicate task as many of the ingredient selections do provide both desirable and undesirable trade-off performance attributes,” Mosier explained. “Compounding keeps evolving as new materials are being developed and new fillers and chemicals are introduced to enhance fuel efficiency, grip, and cut and chip resistance, while also complying with new environmental regulations.”
Depending on the part of the tire — tread, sidewalls, belts, or casing — there can be 30 to 40 ingredients in the various rubber compounds. On average, it takes 22 gallons of petroleum to produce a new commercial tire. Much of that is for the production of process oils, chemicals, synthetic rubber and carbon black. To replace some of the oil, manufacturers are looking at variety of sustainable, natural ingredients as substitutes.
And, minds are always working. Cooper led a consortium under a $6.9 million USDA grant to study guayule — a woody shrub grown primarily in the southwestern United States. They learned it’s possible to extract natural rubber, latex, non-toxic adhesives and other specialty chemicals from the shrub. Cooper built concept passenger tires based on this knowledge, and after extensive evaluation, including rigorous wheel and road tests, the guayule tires were found to have overall performance at least equal to tires made with natural and synthetic rubber. While the purpose of the study was research and not commercialization, Cooper determined it could use guayule rubber in tire production today if enough material was available to meet production needs at a competitive price. (A video detailing this study is available at www.coopertire.com/guayule.)
Another alternative has also been studied — Taraxacum kok-saghyz (TKS), the scientific name for a type of Russian dandelion. Cooper is playing a key role in the Program of Excellence in Natural Rubber Alternatives (PENRA), group dedicated to the development of TKS as a domestic natural rubber source. This consortium, led by The Ohio State University, is making progress in its research, which includes tire compound evaluations. The idea is to breed a type of dandelion that yields a milky fluid with tire-grade rubber particles in its taproot.
“Beyond natural rubber sources, Cooper is continually studying new ingredients that may help improve tire performance. If we believe a material has promise, we will study it for its potential to be put into development,” Mosier said.
In the here and now, compound development has multiple stages. According to Mosier, the engineering team at Cooper puts mixes through a series of test suites designed to correlate with conditions the rubber compound will see during the life of the tire. The most promising rubber compounds are vulcanized and tested under static and dynamic conditions. Cooper’s lab equipment is designed to test small rubber samples at different frequencies under various temperature settings from minus 148 to 212 degrees Fahrenheit (-100 to 100 degrees Celsius).
“Tests to examine factors such as tensile strength ensure that compounds perform as expected and meet or exceed industry safety standards. After the tire is built and cured, it moves to wheel testing on a simulator that mimics real world speeds and conditions,” Mosier said. “Once we are satisfied, field engineers work directly with customers to study how well the tires are performing in the day-to-day environments against our own control products as well as that of the competition.”
Here’s a perfect example: Waste haulers, in major cites like New York, Chicago and Los Angeles, have a very specific job, and in the course of their work, turn tight corners and do a lot of starting and stopping. The application requires a compound that provides excellent wear resistance. Mosier recalled that Cooper had developed a tire compound for waste hauler applications, and it was performing well in testing, but frequent contact with curbs was causing shoulder damage. The solution was changing some of the internal polymers and fillers to improve the tear resistance of the tread cap without affecting the other properties of the tire.
Another example is long haul operations through Northern Canada where snow and icy conditions are the norm, and drive tires need to have superior traction. Here, tread compounds need to provide traction plus low rolling resistance even when the rubber is cold.
Cooper recently launched its Severe Series WBA commercial truck tire that provides long miles to removal, while handling the harsh operating conditions found in construction truck applications. Special cut, chip and chunk resistant compounds, plus Cooper’s Scrub GuardTM technology, help the tire withstand scrubbing, curbs, and other obstacles typically encountered during operations to ensure longer tire life while maintaining casing integrity. For those in long-haul operations, Cooper’s PRO Series features tires that are ultra fuel efficient. A combination of tire design, compounding and construction created tires that exceed SmartWay standard requirements by 15 percent and meet the EPA’s greenhouse gas (GHG) emissions requirements set for 2021.
“Tread design is married to a specific compounding formulation,” Mosier said. “On a truck, you have steer, drive and trailer tires. With three different sets of tires in the setup, each will have different compounds. There can be different tread caps being utilized, and each tire set has a specific need requirement. There might be a tire that would work in all three positions, but it would have a very limited application.
“One of the biggest misconceptions that tire buyers have is that all rubber compounds are the same,” concluded Mosier. “That couldn’t be further from the truth. At Cooper, we never stop working to improve our tires. It all starts with the needs of the customer and ends with our work in the lab to come up with a solution.”