Cooper Tire and Rubber has completed builds of tires made of natural rubber sourced from the guayule plant. The company announced the progress as part of an update on the $6.9 million project, funded by a Department of Energy grant.

The tires are being tested on roads and tracks, and the company indicated that initial tire performance was equal to tires made by Hevea rubber plants, one of the primary sources of natural rubber production.

“We are extremely pleased with the progress that the group has made to advance the guayule technology on all fronts,” said Chuck Yurkovich, senior vice president of global research and development at Cooper. “The team is making rapid progress toward a commercial source of domestic natural rubber and ultimately tires made with guayule rubber.”

Cooper is part of a group using the DOE grant money to research the viability of the guayule plant as a sustainable source of rubber and other products. The group includes PanAirdus, Arizona State University, Cornell University and the Agricultural Research Service of the U.S. Department of Agriculture.

The group aims to use biopolymers extracted from guayule as a replacement for synthetic rubbers and Hevea natural rubber. The grant period will end in 2017.

Earlier this year, Bridgestone opened a biorubber research center in Mesa, Ariz., to study the guayule plant, a native shrub of the American Southwest. Bridgestone hopes to produce fully sustainable and renewable raw materials from that project by 2050.