Racecar Dynamics and Data Acquisition Training Seminar
by Paul Haney
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.
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
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.' "
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
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 firstname.lastname@example.org.