DETROIT—Dave Cowger and his team of engineers at General Motors Co. spent about two years putting tires through a lot of abuse before selecting what they believe are the ideal tires for the 2011 Buick Enclave.
Cowger, GM's tire engineering group manager, heads up a team of about 50 engineers at GM's Tire-Wheel Systems Lab at the Milford Proving Ground.
In the case of the 2011 Buick Enclave, Cowger worked with engineers at Bridgestone and Michelin to develop tires to meet the Enclave's needs for a smooth ride, fuel economy and low road noise.
In the end, GM selected the 19-inch Michelin P255/60R19 and 20-inch Bridgestone P255/55R20 all-season tires to be the original equipment tires shipped on the Enclave.
While GM engineers look for different tire characteristics for different vehicles, the overall process for selecting a tire as original equipment is similar.
“We establish specifications for a tire, along with a size, and all the different performance specifications that are optimized and balanced to match the vehicle,” Cowger said. “Then we go through a technical review process with all of our suppliers.”
In the end, GM usually selects one or two manufacturers to develop a tire for each project.
Testing process
“We'll go through a number of submissions from that supplier before we get to the final tire that meets all of our requirements and passes all of our tests,” Cowger said.
In North America, GM works with six tire manufacturers for passenger vehicles: Bridgestone, Continental, Goodyear, Hankook, Michelin and Pirelli.
Each tire vying to become original equipment on the Enclave went through 25 lab tests to gauge how it would hold up to real-world abuse. Tests mimic blows, such as those a tire might sustain when hitting a curb or pothole.
The tires also were put on a dynamometer with specially grained sandpaper to replicate tens of thousands of miles of road wear.
“That will represent the type of wear you would get on an abrasive road surface, and that allows you to do some of the wear testing, particularly in the early process,” Cowger said.
Scientists also check for air permeation—air pressure loss through the tire. Other tests measure rolling resistance, which helps determine a vehicle's fuel economy.
“They build experimental tire constructions,” Cowger said of the tire manufacturers as they try to meet GM's specifications for a particular vehicle. “They run some lab tests. We run some lab tests. Typically, they'll give us a submission of perhaps four different tire constructions with different features.”
Once the lab tests are completed, GM engineers put the tires on a vehicle for further evaluations, Cowger said.
“We take them through strenuous handling courses, doing maximum lateral acceleration kinds of maneuvers and aggressive lane changes and avoidance maneuvers,” he said.
GM also conducts ride-comfort tests over different types of surfaces and measures in-vehicle noise levels, and conducts treadwear tests to calculate how many miles an average driver should expect from their original set of tires.
The treadwear test lasts for 25,000 miles, but the engineers are able to use that information to calculate the tread life of the tire.
Engineers then report the results of their tests to the tire manufacturer, who makes further adjustments to improve the design of the tire and its composition to meet GM's needs.
Criteria varies
While the testing procedure for all vehicles is similar, the criteria on which engineers place their emphasis will vary by the car type, Cowger said.
“You have to balance those requirements so it's got the right balance of performance for the vehicle and the market that the vehicle is selling in,” he said.
For example, while low-road noise and a comfortable ride are important to drivers of an Enclave, drivers of a Corvette sports car place a higher emphasis on handling and performance from their tires, he said.
For drivers of a Chevrolet Cruze Eco, an economy car that can deliver up to 42 miles per gallon, reduced rolling resistance is of major importance because it boosts fuel economy, he said.
Engineers have to accept a certain tradeoff of features, Cowger said.
Meanwhile, tire manufacturers can spend $1 million or more for each tire they develop for a specific car model, said Mike Martini, president of the Consumer OE Division of Bridgestone Americas Tire Operations.
“Every tire that we manufacture for an OE is made to their overall specifications, and it's a very grueling process, where literally hundreds of tests are done on our side and the OEM's side to ensure that the tire fits the character that they're looking for very specifically in that particular vehicle,” Martini said.
The testing begins even before Bridgestone develops a tire prototype. Engineers first simulate the tires with finite element analysis modeling. It involves using a computer to determine how a tire will roll on a particular car model.
The results are provided to the auto maker, and after receiving their input, Bridgestone begins manufacturing prototypes so the auto maker's engineers can see what it actually feels like on a vehicle.
Key challenge
One of the challenges Bridgestone faces is that as auto makers tweak the design of their vehicle, “we need to make a change based on the changes they're making as the vehicle is being developed,” Martini said.
Bridgestone has its own test facilities, both indoors and outdoors, in Fort Stockton, Texas, and Acuna, Mexico. Also, a sophisticated tire development center is located in Akron.
Michelin, the other company to produce tires for the Enclave, may spend between six months and two years working with an auto maker to develop a tire for a new vehicle, said Dean Weekes, Michelin's product marketing manager.
The tire maker's engineers work with their counterparts at the auto maker to ensure tires match vehicle suspension for best performance, Weekes said.
“It's a large portion of our research and development campus located here in Greenville, S.C., as well as in similar centers in Europe and Asia,” he said.
Seventy-five to 90 Michelin engineers and related employees in North America work on developing new tires for auto makers, he said.
“It's a customization process,” Weekes said. “I make the analogy of buying a tailored suit.”
It's very rare that an auto maker introducing a new car will settle for a tire pulled off the shelf, he said. That only happens in a “crunch situation.”