Shaker Test Data
The numbers on the bottom and left of the graphs represent
the increments of adjustment (detent clicks) from full hard for
the front and rear shocks. At the lower left of each graph all
the shocks are set for high forces and at the upper right they
are all set full soft.
"We process the data statistically to minimize error,"
explains Hedlund. "Then we graph it as colored gradient
lines. The bar on the right shows the overall range. A change
0.84 to 0.85 is something the driver can feel on the track. 0.85
to 0.90 is a big change. The graph is like a map. Blue is better,
red is worse. The spacing of the lines is the gradient.
"Looking at each corner is an overall view. The lines
show front-to-rear coupling if there is any. This is usually
not the case in stock cars but open-wheel cars can have a lot
of front/rear coupling. A shock change at the front can affect
the rear of the car.
"The pitch dynamic balance chart compares the characteristic
of the disturbance of the front and rear of the car. In the end
the team needs to compromise and choose between optimum grip
or minimum pitch disturbance. On a bumpy track they might minimize
pitch. Driver feedback and a stop watch tells what works. Formula
1 teams allow pitch in search of more grip because most of the
tracks they run on are so smooth. The Speedway at Indianapolis
is smooth but there is enough high frequency disturbance on the
track to excite a car in pitch."
This first group of graphs shows grip disturbance data from
each corner of the car during a low-speed test. The narrow vertical
bar on the right of each graph is the range of the grip disturbance
characteristic as calculated by the Öhlins method. Blue
is better, red is worse. The graphs of the two front corners
show lines running vertically corresponding to front shock adjustments
and the lines on the two rear graphs are horizontal. This means
the two ends of the car are decoupled.
The blue colors show stiffer damper settings are better. The
numbers represent clicks from full hard so lower numbers are
stiffer settings. The small distance between some lines and colors
shows that relative disturbance can go from good to bad with
just a few clicks of shock adjustment
The second batch of data emphasizes pitch disturbance. On
the top two graphs, depicting front and rear grip disturbance,
the lines show that the front and rear of the car are decoupled
and stiffer shock settings are better. The overall graph also
recommends stiffer shock settings. But the pitch dynamic balance
graph is more complicated showing an area of concern in the region
of stiff front/soft rear settings. This is where compromise choices
and track testing helps with the decision.
"We can input forces to the tires at higher frequencies
than other methods," Hedlund said. "We're focusing
on the tires, using the spring and damper to control the tire.
You'd rather give up some body control to optimize tire forces,
but driver feedback determines how far you can go in that direction.
You're always compromising in racecar setups so the gradient
format of this data is useful. The data becomes another tool
the team can use to drive compromises."
Racing is complicated. Race engineers need all the help they
can get to help them find setups with more absolute grip and
more controllable grip. Driver comfort will always be important.
Compromise dominates the decision process.
Race teams need answers and dynamic testing is another tool
providing data. The Öhlins method of data presentation shown
here gives a test customer something to take away that points
toward better and worse adjustments. But, as Mats Hedlund pointed
out, on-track correlation is still necessary.
At the moment Formula 1 teams depend heavily on shaker rigs
for both reliability testing and setup generation. CART teams
also use shaker-rig testing to point them toward spring/damper
combinations that minimize pitch sensitivity and maximize grip.
But race teams without shaker-rig experience might need to
generate a leap of faith in order to commit to a seven-post test.
But many top teams, both open wheel and stock car, are confirming
shaker-born setups with track testing and race results. Shaker
rigs seem destined to follow in the footsteps of wind tunnels
and become a must-have tool for top-level professional race teams.
Contact Ohlins in No. Carolina at 828-692-4525.