One Step Ahead

Feb. 6, 2003
The quest for an edge is a constant part of NASCAR's ultra-competitive Winston Cup circuit.

The quest for an edge is a constant part of NASCAR’s ultra-competitive Winston Cup circuit.

A competitive advantage in NASCAR's Winston Cup Series is a fleeting thing. Teams that have one don't have it for long. The National Association of Stock Car Auto Racing (NASCAR) keeps an eagle eye on the happenings of each race, making sure cars stay competitive. And, if that means giving a little here on spoiler sizes, or adding a little there with air-dam clearances, so be it. Most manufacturers and teams accept these real-time changes as the nature of the beast. But that doesn’t stop them from constantly looking for an edge. Teams work closely with NASCAR’s Winston Cup car manufacturers, Chevrolet, Pontiac, Ford, and Dodge, refining their aerodynamic packages for every track. It’s a constant case of trial and error blended with old-fashioned ingenuity and modern-day science and technology.

New Editions

The big news this year comes from GM Racing, which is rolling out new models of its Pontiac Grand Prix and the Chevrolet Monte Carlo. Development of the new race cars was a total team effort between GM Racing, its core teams, and NASCAR. The Grand Prix had been in the works for a couple of years before receiving NASCAR’s approval last June. It will make its racing debut at the Daytona 500. GM Racing brought NASCAR into the development loop early on, explains Ray Smith, Pontiac program manager for the NASCAR Winston Cup and Busch Series, GM Racing. “We informed them that we’d be having a new model car on the street and that was the car we wanted to race at Daytona.” To ensure next-generation cars, such as the new Grand Prix, conform to NASCAR rules, manufacturers are issued a set of aluminum templates that define the outline of the car right down to its centerline.

Pontiac brought in Joe Gibbs Racing as the lead manufacturing team for the new model, as well as MB2/MBV Motorsports. One key design goal was keeping the brand character of the car obvious to fans. "We tried to maintain the front and rear fascias and make sure all of the window openings were basically the same as the street car, because those are all things people read from a distance," explains GM Racing's Terry Laise, lead aerodynamics engineer.

GM Racing engineers worked with top NASCAR teams to develop the bodies of the 2003 Pontiac Grand Prix and Chevrolet Monte Carlo.

The Gibbs team built the submission car, tested it in the wind tunnel, and helped GM shape the front and rear fascias and other features unique to Pontiac. NASCAR Winston Cup teams build two different cars for competition, one for downforce tracks and one for superspeedways. For the new Pontiac, Gibbs built the downforce car and MBV tackled the speedway version.

Cars built for downforce race on short or intermediate tracks where handling is critical and drag isn’t as big a factor because cars run at full horsepower. NASCAR strictly regulates overall length, width, height, wheelbase, and spoiler sizes, so manufacturers and teams are limited on how much they can do to get more grip. "With downforce cars, we try to get as much high pressure as possible over the topside of the car and as much low pressure as possible underneath," says Laise. "We do that to keep air from getting under the car and to keep air over the car acting in a positive pressure way, where the airflow is not speeded up." Teams will often vary the cars' panels to create more pressure on the track surface. Also, cars built for downforce generally have more pronounced front fenders and larger grill openings than speedway cars to get more cooling air to the engine and brakes.

The competitive nature of Winston Cup racing often has cars running just inches apart. Stability is key, says GM. "Pitch is a measure of the lift at the front and rear of the automobile. Yaw is a measure of stability, like an airplane turning from side to side," explains Laise. "A van that wanders from side to side on a windy day is an example of what happens when the center of pressure is far from the yaw center of the chassis. Ideally, we tune these variables so a race car goes down the track like an arrow."

Drag is a drag

Speedway cars are all about low drag. "NASCAR teams are concerned about aerodynamic drag because it has such an impact on speed," says Laise. "When a car is running at 200 mph, improving its coefficient of drag (Cd) by just seven counts, a 0.007 reduction on its Cd, adds one full mile-per-hour to its speed." Obviously, any gains in aerodynamics or engine performance on these tracks are particularly vital. To get faster laps from speedway cars, teams try to make them as small, smooth, and streamlined as possible. "Speedway cars usually have rounded fronts, a sharp trailing edge, and are designed with an emphasis on minimizing the amount of air getting to the rear spoiler," says Laise. Teams go over their vehicles with a fine-tooth comb, looking for any way to cut drag by doing such things as tucking in the front fenders and smoothing out any bumps. Before, 2002 teams had more aerodynamic leeway because they were allowed to float the whole body fore and aft on the chassis: They moved it back to cut drag and forward to increase downforce. NASCAR now regulates the body-location package. "The body is now located, with respect to the wheels, in the fore and aft direction ± 0.5 in.," says Laise. "In the past when there was no rule, cars actually varied ± 4 in. It has been quite a change, aerodynamically, for the race cars."

Seven hydraulic actuators simulate the suspension and aerodynamic forces that affect a race car at speed. Similar systems evaluate ride and handling.

GM's experience developing and building the 2003 Pontiac Grand Prix paid off when it came time to build the new Monte Carlo. As with the Pontiac, GM worked side by side with NASCAR and a select group of teams that included Hendrick Motorsports (HMS), Dale Earnhardt Inc.(DEI), Richard Childress Racing (RCR), and Joe Gibbs Racing. Interestingly, the Monte Carlo was not slated for a model change but some owners felt the previous car was laboring in a slight aerodynamic disadvantage on the racetrack, explains Laise. "They pointed out that it would be better to take the car under the rule package NASCAR had developed in moving forward rather than leaving the car as it was until a model change came about," he says. "So we started the project in March '02 and had the car approved by that same summer." GM says the new Monte Carlo is unmistakable, sporting its distinct features including a sloping hood, front and rear fascias, rear-quarter glass panels, short rear deck, and a sleek overall shape.

Last October, GM got the green light from NASCAR for a two-day test of the 2003 models of the Monte Carlo and Grand Prix at Talladaga Superspeedway. Eleven cars were tested by well-known drivers, including Dale Earnhardt Jr. and Bobby Labonte, in front of GM and NASCAR officials, as well as crew chiefs from the core development teams of HMS, DEI, RCR, and Joe Gibbs Racing. Everyone involved gave the tests high marks. GM says other track tests are being run as well as wind-tunnel testing.

No one sitting still

The new Monte Carlo and Grand Prix will match up against the Dodge Intrepid R/T and Ford Taurus. Dodge came roaring back into Winston Cup racing in 2001 after a 25-year hiatus. In just two years, the Dodge boys have become a force to be reckoned with, capturing their fair share of top spots and victories. This year the Dodge camp grew as Penske Racing South joined the ranks. Team owner Roger Penske will field the No. 2 Miller Lite Dodge driven by Rusty Wallace, and the No. 12 Alltel Dodge with 2002 rookie of the year Ryan Newman at the wheel.

Ford Racing has had huge success running the Taurus and has no plans to change that anytime soon. "The Taurus has gone through a couple of developmental evolutions and it is now a very competitive piece," says Greg Specht, Ford Racing manager of racing operations. In fact, claims Specht, when Ford introduced its Taurus to NASCAR in 1998, the car was established as a shape standard for all Winston Cup manufacturers to follow. With regard to templates, though tolerance is built in, “Race teams will take advantage of that tolerance to the extent that they can improve the aerodynamic performance of the car," says Specht. "Most people think stock-car racing is crude in terms of not being precise, and using old push-rod engines. But I am amazed that, for example, NASCAR has a tolerance of a thousandth of an inch on a certain dimension and teams will identify an end of that tolerance that brings better performance. They'll build the engine at the tolerance limit to get every last bit of performance."

NASCAR officials carefully scrutinize spoiler height and angle during technical inspections to ensure a level playing field.

Testing and simulation have also gotten larger roles in recent years. "Technology has really come to the fore in the testing and analysis portion of race-car development," says Specht. CFD, for instance, plays a huge role in studying how air flows over the car. "CFD studies tell us the pressure over the whole car surface and show us where we need to look if we are trying to reduce drag or increase downforce," Specht explains. "From the computational work we'll go to the wind tunnel, for example, for testing to make sure we have equal pressure over the front and rear wheels, and we also use CFD and wind-tunnel testing to examine individual wheel loads and side forces."

Manufacturers also run tests on the suspension using what’s called a Seven Post test. The test simulates how the suspension performs dynamically using a rig with a hydraulic actuator at each wheel that moves the suspension up and down at any desired frequency. Three other actuators measure cornering and aerodynamic loads to the car. Another common test uses machines to actually twist and bend the chassis. This lets engineers measure chassis torsional and bending resistance, center of gravity, and moment of inertia. Ford also uses proprietary race-simulation software.

Though teams do some of this testing themselves, they obviously don't have the resources of a Ford Motor Co. That said, team personnel are "Very intuitive about what does and doesn't work on a car," continues Specht. "So they come up with ideas, and build pieces that they'll place on the car in the wind tunnel to see if there is improvement."

Oftentimes ideas come from seeing what other teams do in their garages, a practice encouraged by NASCAR. "To keep the racing competitive, team cars are parked right next to each other in the garage so each team can look at the other cars, see something they didn’t see at the last race, and try it out themselves," says Specht.

For safety reasons, NASCAR has limited horsepower at the superspeedways, such as Daytona and Talladega, through the use of restrictor plates. Restrictor plates - small, 1/8-in. plates of aluminum bolted between the carburetor and the intake manifold - have four small holes punched in them and sit under each of the venturis in the carburetor to restrict airflow to the engine. The plates cut engine power from about 775 to about 420 hp. Safety is a critical element of stock-car aerodynamics. Roof rails, roof flaps, and side windows are designed to keep spinning cars from going airborne.

Many times, what manufacturers and teams learn from their race cars translates to the showroom floor. "It is very much a two-way street," says Specht. "For example, Ford is a leader in crash safety and we are working with our race teams and NASCAR, sharing what we've learned about crash safety in stock cars. We believe it will shorten the development curve within NASCAR. On the other side of the coin, the race teams and Ford Racing do a lot more wind-tunnel testing on the car than production people can. So we've learned things about the Taurus that they haven’t had time to discover."

One and done

At the start of the 2002 racing season, NASCAR eliminated the use of practice and qualifying engines, instead requiring teams to use the same engine from the start of practice throughout the race. With the new rule, engine durability became a big concern. Teams accustomed to changing engines prior to the race now had to consider how hard one engine could run before critical components would fail. The standard NASCAR engine is a maximum 358 in.3, two-valve push-rod type, with an 830-cfm carburetor and maximum compression ratio of 12:1. Says GM Racing's Jim Covey, NASCAR engine-development manager, "Earlier in the year, guys were more conservative, not knowing how the additional engine cycles that are run during qualifying and practice would affect the durability and reliability of their race package. They had a pretty good idea of what it took to make a fresh engine last through the last practice and a 500-mile race, but they had no idea of what was going to happen in the qualifying procedure." Typically, teams have two practice sessions, then qualifying, followed by a couple more practice sessions, and then the race. During qualifying, to improve aerodynamics, teams tape up front-end areas, restricting air into the radiator, "That thermal cycles the engines," says Covey. "And with the front-end of the engine fully taped off, you can only run about two laps before it starts overheating." Between such runs, teams circulate cool water through the engine to bring the temperature down. Thermal cycling continues throughout the qualifying session, stressing engine components.

The one-engine rule also took away some of the liberties teams could take with the qualifying engines, says Covey. Knowing they were going to eventually pull the qualifying engines out let teams push the envelope and try different designs: Changes that wouldn't last for 500 miles but could get a car through qualifying. "That was their chance to do some engine R&D but they lost that luxury," he says. "However, as the season progressed, guys got more comfortable with using one engine all weekend and are now back on track."

Watch the wheels

The sheer weight of Winston Cup cars (3,500 lb) and the load they put on the tires makes tire management a key issue. Goodyear is the sole tire supplier to NASCAR's top three series: Winston Cup, Busch, and Craftsman Truck. Goodyear's Rick Campbell, team leader for the NASCAR programs, explains the weight factor. "The weight of the car translates into increasing dynamic load, particularly with the banking that Winston Cup cars run on," he says. "The banking is different track to track. Homestead, for instance, is a fairly flat track with somewhere from 6 to 9° banking. Talladega, on the other hand, banks at 33°. Though there are many examples in the middle, a typical Winston Cup bank angle is about 25°."

Load on the tires increases too as teams continually try to gain more downforce in the wind tunnel. “The duty cycle of the tires continues to evolve and become more severe,” explains Campbell. “It’s imperative that we stay a couple of steps ahead of the teams to make sure what we provide them can handle what they are going to need.” To determine those needs, Goodyear engineers are in constant contact with teams, making sure they understand what the tire is being asked to do, and to ensure the tires are being used properly.

Because Goodyear fields the entire series, designers don't have to be as concerned with lap times or gaining more speed, says Campbell. What they are concerned with, however, is safety and making sure their tire designs can handle the conditions in which they operate. For example, Winston Cup cars are fairly grip limited in that they slide around the track a lot because there is so much on-throttle, braking, and off-throttle. "It is critical for us to design a tire that goes through these transitions smoothly and easily," explains Campbell. "When the car is sliding we have to make sure the driver can still feel the car through the slide and balance it out."

Differences in track surfaces also garner significant design consideration. To determine what tire setups to use, Goodyear organizes the tracks into groups that require similar tire setups, and then takes the toughest operating conditions within a group of tracks and applies that need to everything else. "For example, one group of tracks includes Rockingham, Darlington, Las Vegas, and Bristol," explains Campbell. "Bristol provides the highest amount of load but Darlington is the toughest when it comes to surface and abrasiveness, so in this group, Darlington becomes our benchmark. We would design a tire that handles Darlington and probably give up a little bit of performance and grip at other tracks. We've tried, based on our experience at the various tracks, to come up with four or five different groups of tracks to which we can apply a common tire setup."

Goodyear relies on drivers and teams to help pinpoint tires that produce results. The tiremaker contracts with teams to test tires on a series of laps and takes their feedback, along with other measurement data, comparing that to tires raced at the same track previously. This lets engineers see if they've made any gains. Goodyear further communicates with teams, and NASCAR, regarding upcoming rule changes and how new car designs fare in wind-tunnel testing. This keeps Goodyear a step ahead in tire design. "We have to be prepared for changes," says Campbell. "That's why it's important for us to have open lines of communication with both NASCAR and the teams."

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