Yokohama Tire has in the meantime developed tires that are 80 percent petroleum-free, says Dan Guiney, director of technical services. The company's dB Super E-spec car tire and its ADVAN ENV-R1 racing tire both use modified natural rubber compounds and processing oil that is derived from orange peels, a waste by-product of fruit juice processing. The company, which introduced the dB Super E-spec orange oil-infused model last year, reportedly charges roughly 30 percent more for the green tire.
Michelin says that it employs sunflower oil in the rubber compound of its premium Primacy MXM4 all-weather tires to improve traction in winter conditions and shorten braking distances in the rain.
Other tire-makers are looking beyond traditional rubber trees to develop new, potentially cheaper and more sustainable crop sources of natural latex such as Russian dandelion, a central Asian weed variety, and guayule, a desert shrub that grows in the U.S. Southwest and Mexico, Herzlich says.
Still other companies are turning to renewable synthetic rubbers made of precursor chemicals that are grown in vats by biotech-modified microorganisms. In 2007 Goodyear entered into a research collaboration with the industrial biochemical firm Genencor of Palo Alto, Calif., (a subsidiary of Danisco, a Denmark-based food ingredient company) to develop microbes that can grow the isoprene monomer, or what the company calls BioIsoprene, says Rich LaDuca, senior director of business development at Genencor. Goodyear will use the BioIsoprene to cook up a synthetic rubber that mimics natural rubber, which is composed of polymerized natural isoprene. The biotech firm will offer to supply the sustainable chemical to other tire manufacturers as well.
A research group at Oregon State University recently reported that microcellulose, or microcrystalline cellulose, which can be made from various plant fibers, provides a promising alternative to the heavy (and costly) silica mineral fillers now used to reduce tires' rolling resistance. The lightweight microcellulose could save even more fuel. More study is needed, however, to confirm the long-term durability of tires that incorporate this natural additive.
In the meantime, the tire industry is trying harder to recycle more of the estimated 300 million used tires that are discarded annually in the U.S. Tire recycling has grown markedly in recent years and small quantities of processed rubber are reused in some tires, but these efforts are limited by the quality of the rubber feedstock, Herzlich says. One company, Georgia-based Lehigh Technologies, has developed a process that freezes the rubber with liquid nitrogen before grinding it into pulverized rubber feedstock that could go into tires.
In time, the ongoing installation of new precision tire-making machinery that can hold much tighter manufacturing tolerances will allow tire-makers to produce tires that have little extra weight beyond the design spec, Herzlich says. "If you take a half ounce out of a tire," he explains, "it saves fuel because it makes it easier to rotate the wheel."
Although the overall environmental legacy of the car tire is still decidedly black, the appearance of fuel-saving designs, biosourced raw materials and more vigorous recycling programs have given its future a distinctly greener hue.