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Racecar Dynamics and Data Acquisition Training Seminar

This article will appear in Racecar Engineering this Spring.

Racecar engineering is so complicated that most people have given up hope of gaining any significant understanding. Many people involved in the sport don't even try to figure out why anything works but instead keep meticulous records on set-up variables along with track conditions, driver comments, weather, and other minutiae. They rely on that recorded information and their experience for starting setups at tracks they know.
NASCAR teams are famous for having magic sets of springs and shocks that work at one particular track and get stored carefully and installed on the car again when the team goes back to that track. Some club racers don't change the car at all when they go to a new track.

People involved in the technical aspects of racing try to understand what's going on but realize the complications. They develop a set of personal beliefs about how the racecar works that helps them most of the time. When new information arises the most open minded of this group quickly shed their old beliefs or modifies them to embrace the new data. During race weekends they are willing to modify their system minute by minute in the face of evolving reality.

Where do the new ideas come from? Maybe a different tire construction or compound or a driver new to the team forces the exploration of new combinations of tire pressures, spring rates, anti-roll bar rates, suspension geometry, shock forces or aerodynamic changes. Off-season repairs to a race track or a complete repaving can significantly change the behavior of tire/track interface. A team that qualified on the front row can be faced with an ill-handling racecar just hours later because of a rain shower. A good team faced with the need will adapt rapidly.

Blessed Mystery

Aerodynamics used to be a great unknown but the proliferation of wind tunnels and high-tech instrumentation has shed much light on this topic. But it seems there actually is no real hope of learning anything technically significant about racing tires. Tire design is so subjective and so dependant on how the tire feels to the driver that most of the data available is empirical instead of analytical or predictive.
Tires seemed doomed to remain a mystery. And you might as well put the driver and the dampers in that same category. Happily, these three very important components of racing continue to defy analysis and will for the foreseeable future provide the bulk of the challenge of motor racing.

Data Analysis Sheds Some Light

Accurate and reliable data acquisition systems provide vast quantities of information, but few teams have the time to analyze even a small fraction of the data amassed. Formula 1 teams might be the exception. With their vast budgets they write software to solve all problems and calculate all solutions. They too, however, still have to live with that mysterious triumvirate of tires, driver, and dampers.

Racing people can be extremely secretive and paranoid. The simplest technical questions can bring out misinformation or outright lies. Even the right question doesn't always get a good answer. This attitude restricts the flow of information, but protects the ignorant.

There is, however, some light at the end of the tunnel. Pi Research, a company providing data acquisition and analysis systems to all levels of racing, is helping to promote a seminar that provides ground-breaking information. Claude Rouelle, a race engineer for 20 years, uses his new seminar to explain some basic vehicle dynamics and show how the analysis software in the Pi data acquisition system can produce definitive numbers that reveal some useful information about racecar behavior.

Pi Research sells and supports data acquisition hardware (on-board computer systems), data acquisition and analysis software, and sensors. With these products racers from the highest professional levels to the weekend kart competitor can learn about the race vehicle and improve its performance. They decided to support Rouelle's training seminar because they saw their customers were not getting full benefit from their products.
After only a few months this seminar has had rave reviews by race engineers, data technicians, and motorsports managers. CART and IRL teams have sent engineers to the seminar, and both Ford and General Motors have scheduled seminars in Charlotte, No. Carolina for NASCAR teams. Racing tire manufacturers Goodyear and Michelin have also had Rouelle present his training to their engineers.

Ignorance is a Reality

Claude Rouelle earned a Mechanical Engineering degree from Institut Gramme Liege in Belgium and started his own company building and racing Formula Ford racecars. He has worked as an engineer with European Touring Car, Formula 3, Formula 1, Japanese Formula 3000, Indy Lights, and several CART teams. After he decided to develop this seminar he worked for six months preparing his presentation using Microsoft PowerPoint software. "I could probably teach PowerPoint now," Rouelle said.

"The facts are that racecar vehicle dynamics are not well understood," Rouelle explains. "There are no dumb guys in racing, just a lack of knowledge in some specific areas. There are no schools to go to that teach you what you need to know. As racing grows more popular the need for good engineers increases. The cost of racing is going up and there is a need to utilize the equipment more efficiently.

"The basics of vehicle dynamics and the use of data acquisition software is not THAT complicated. It can be taught in a few days. The need is clear. Only the top professional race teams with big budgets can afford proven, experienced engineers. These guys make annual salaries of 100 to 300 thousand dollars now. Most teams hire young, highly motivated engineers who lack the experience of the seasoned guys.

"Who's going to teach these young engineers what they need to know? Team managers or crew chiefs aren't usually trained in engineering, and most engineers won't share critical knowledge. What I do in this seminar is share my knowledge and experience in racecar engineering. It's not that we tell them any tricks, you need to understand what you're working with so you can deal with all the changes and unknowns in racing. I think it's almost as bad to be on the pole and not know why as it is to fail to qualify for a race and not know why.

"I think there are two very important points to make that illustrate the importance of arriving at the race track with a good beginning setup. My favorite saying is, 'The less you do the fewer mistakes you make.' " Pi's favorite saying is, 'The more you know the faster you go.' "

Seminar Details

This course is designed for race engineers, crew chiefs, and data acquisition technicians. But drivers, tire engineers--any person involved in technical racing projects-- will benefit from the learning experience.
A three-day program, the seminar presents racecar vehicle dynamics and data acquisition in two parts. The first part covers definitions, tire parameters, aerodynamics, kinematics, dynamics, brakes and gear ratios, and math channels in the Pi software. The second part of the seminar presents how to get started; logging, scaling, and filtering; interpreting data traces; driver aids; special sensors; teamwork; and choosing a Pi system. Pi Research also offers a separate seminar providing an additional day of training in applied sensor science.

Vehicle Dynamics and Magic Numbers

The way a racecar uses its tires has to do with lateral and longitudinal weight transfer. Rouelle explains weight transfer in simple steps starting with how to use the Pi system to determine the center of mass of the car. He shows how to determine the sprung and unsprung masses and the location of their centers of mass. This information used with the suspension geometry yields some interesting information.

When a car steers into a corner and the tires assume some slip angle they develop lateral forces that transfer to the chassis through the suspension links. Rouelle differentiates between "elastic weight transfer" and "geometric weight transfer." Geometric forces go through the suspension links into the chassis as soon as tire forces begin. Because the instantaneous center of rotation of the suspension is probably below the center of mass there is a roll moment that wants to rotate the chassis about that center of rotation. The springs and dampers control the timing of those "elastic" forces, but they build up after the start of the geometric forces.

This graph shows how the forces build up with time. The front tire takes about a half-turn to assume a full slip angle after a steering input. If the rear tires were not fixed they would rotate as if on casters and the mass at the rear of the car would spin out. But the rear tires are fixed and, after some delay of their own, they assume a slip angle sufficient to hold the car in the radius of the turn. After the front and rear tires have taken on a slip angle they feed lateral forces into the chassis through the suspension links. Rouelle calls this the geometric forces.

But the center of mass of the chassis is probably above the center of rotation of the suspension so there is a force trying to roll the chassis toward the outside of the turn. This roll force is delayed by the resisting force of the springs, dampers, and anti-roll bars. The chassis also has some inertia which slows down the transfer of forces from the inside tire patches to the outside tire patches.

Rouelle shows how to use the data acquisition system to analyze and quantify all these forces. He also reveals some "magic numbers" that a race engineer can use to point a direction to go if other feedback is exhausted. One of these numbers is the total spring rate of the front wheels, including tire spring rate, vs. that same value for the rear wheels. Rouelle says, "For a certain driver in the same car at a particular track under similar conditions, this number will be a constant. If you get lost in your setup this number might tell you what direction to go to get back to the sweet spot."

Probably only a few race engineers know all the information presented by Claude Rouelle's seminar. And even those engineers might benefit from an organized presentation of what they think they already know. For more information and a schedule of classes and locations call Pi Engineering in Indianapolis, Indiana, USA at 317-259-8900 or Claude Rouelle in Denver, Colorado, USA at 720-489-9923. Rouelle's email address is claudero@aol.com.