At a recent test session at...
At a recent test session at Concord Motorsports Park we were able to apply some of what we preach. Track testing is how we get better. A plan is developed and data is collected accurately in order for the team to properly analyze what went on and what changes made the most impact, both positive and negative. That is how we learn.
Track testing provides an opportunity to dial in the car to a particular track for speed and consistency. Most events don't offer enough time for adequate evaluation of our chosen setups, so we need to take advantage of every chance we get to go testing.
We recently tested at Concord Motorsports Park with our USARacing project car that John Gibson will drive. What we learned was that the basics don't change even with some of the new and innovative setups we now see in this, and other, series. Suspension alignment problems and unbalanced setups will still throw off your test results.
Testing is a process that should follow a specific order to get the most out of the experience. Let's look at how we might organize and run a typical test session and discuss methods and procedures that you can use for a more productive session. The process is mostly the same for dirt or asphalt with small differences.
All testing and practice involves choosing a setup and chassis geometry that might make the car faster. We are searching for an unknown by making intelligent choices in reasonable directions. What we don't want to do is start out with a car we don't know very well and throw springs, and so on, at it hoping for a miracle. The top race car consultants would never work with a car that they don't know critical information about.
The overall goal of testing is to find a setup combination that will be both initially fast and also stay fast for a long time. It should be good on the tires, comfortable for the driver, and outrun the competition all the way to the last lap.
On asphalt, the setup we end up with is probably the one we'll qualify and race with given small changes between the two. For dirt, the changes required for each segment might be much different. That doesn't mean we can't test on a track that is consistent.
Dirt testing involves trying various settings and bolt-on parts to find what makes the car do what we need it to do. If we can get the car to turn better, that will help us all throughout an event. If we find methods of adding forward bite, then we can get off the corners better for the dry and slick conditions.
Before our test, we had the...
Before our test, we had the team from RaceWorks install PI data acquisition components so we could monitor all of the vital functions on the car for later evaluation. We had shock travel sensors, load sensors, g-force in X-Y-Z axes, as well as steering montoring. This data would later provide us with the needed information we could use to run the seven-post rig to refine our choices.
A primary goal might be to just learn the process of making changes to meet the track conditions. There's an order and logic to adapting to changing track surface grip levels. Becoming comfortable with making those changes can be a huge performance gain.
It's most important to know your car before you go to the racetrack for practice or testing. This means that you would have already evaluated the front and rear geometry, aligned the car, and done a dynamic analysis of the spring combinations to balance the two suspension systems. We should have tested and dyno'd the shocks, rated the springs, checked the steering system for Ackermann, weighed the car, and prepped the motor.
Take into consideration the type of racetrack if you haven't been there before. If it has a different banking angle than you're used to, a different moment center design might be in order. High-banked tracks have little need for traction-enhancing technology, so plan out your rear steer characteristics and ride height if excess chassis travel is an issue. If the track is flatter, include methods of creating bite off the corners into your planning.
If the length of the test track is different than you're used to, calculate a rear gear that would be in an acceptable range or contact a team that has run the track and ask it about gear ratio. If you're testing on dirt, pick the correct tires for the anticipated conditions.
We mostly adjusted the rear...
We mostly adjusted the rear roll center using the right side Panhard-bar adjuster. When we developed our setup back at the shop, it was very close to ideal and we mainly made small adjustments due to tire temperature data telling us that the setup was "setup loose" as opposed to crossweight loose.
In the days before we leave the shop we must prepare a plan of attack which defines what changes we'll make in what areas. This can be on paper or by making mental notes. The plan should be discussed with the entire crew so the members can have input into the process as well as being able to know the direction the test will go so they can be prepared in their particular areas of expertise.
Having a prepared plan is very important for getting good results. As the test proceeds, each change can be noted as to the results, both positive and negative. We learn probably more from the negative results than from the ones where gains are made. That's because we more readily remember losses in lap times and how to avoid those things that the car doesn't like.
If different combinations of spring rates are to be used, weight the car with each combination of springs and note the position of the spring adjusters, be it the coilover rings on the shocks or the jack screws used in the big spring cars. That way, we can quickly make spring changes at the track and be sure the weight distribution hasn't changed.
We need to mark the shocks as to the corner of the car they will be used on, as well as to their set numbers if we intend to compare different layouts of shocks when making individual corner changes. The tire sets must be marked as well so that we don't mix tires among sets. Using a tire of a different age than the other three (meaning date or laps used) can throw the setup off quite a bit. Many tests have been upset by the use of an odd set of tires.
Once we have arrived at the track and unloaded the car, we need to establish a pitting position for the car that is relatively level. We should have easy access to the tool cart as well as the trailer and other track facilities that may be needed. Mark the spots around the tires with duct tape so you can always park the car in the same position after each run.
You should level the scales in that location and note the ride heights and weight distribution. This will ensure that you'll always know the correct values for your weights.
Weight the car before testing and after all of the testing is done at the end of the day, reweigh the car to see how the weight distribution might have changed from the various adjustments.
Our USA Racing car was equipped...
Our USA Racing car was equipped with Ohlins shocks which were rebound adjustable. Note the black dial at the bottom of the shock just above the Heim joint. We made good use of the wide range of adjustment we got from our shock partners, RE Suspensions and Jason Enders located in Mooresville, NC.
How to Measure Track Performance Once we hit the track, we need to be able to measure our on-track performance. There are two components to speed, the motor/drivetrain combination that gets us down the straight-aways, and the chassis setup combination that gets us through the turns. Since we work on these separately, we need to measure them separately.
A car can be the fastest one in the turns and be off down the straights due to a number of reasons. If we have lap times that include turn segment times, we can then compare our times with our competition. Turn segment times tell us all we need to know about chassis setup experimentation.
You should always take turn segment times in addition to total lap times and make comparisons of both to other fast cars. Remember that if we can improve the mid-turn speeds, we'll usually also improve the straightaway speeds. It's generally accepted that speed gained in the turns is carried all of the way around the racetrack.
If using previously run tires, take into consideration the age of the tire when making comparisons to other cars. If we start on stickers and then run 50 laps of testing, we can expect to lose time to the tires. If our lap times stay consistent, then the changes we're making are probably increasing our performance. Eventually switching to newer tires will show the positive results of our changes.
Don't chase a competitor who has newer tires than you. If we struggle to make adjustments to try to make up the 3 or 4 tenths difference in tires, we could well be putting our setup out in left field, never to return.
Taking and recording turn...
Taking and recording turn segment times will allow you to directly compare your performance in the turns to your competitors' times. Turn segment evaluation tells us when we are set up correctly better than lap times that include straightaway acceleration.
The First Set of Runs
The driver should initially make several slow five-lap circuits and then five faster circuits runs to "shake down" the car the first time out. This establishes that the brakes work as expected, the wheels are on tight, the air will stay in the tires, there are no water or oil leaks, and the transmission and rearend lubricants will be brought up to temperature. We should do two more five-lap runs following the initial outing before we'll be able to get meaningful tire temperatures.
After each of these runs, record the tire pressures and/or temperatures, tire sizes, engine water and oil temperatures, and number of laps run in each session. Make hard copy records of the data in addition to digital records (stored in the tire temperature/pressure box or a computer). It's fine to have digital records, but we all know how easy it is to loose digital information. Doing both is the best way.
Once the driver is confident that the car is sound, longer and faster runs can be done. As you make your next series of runs, try to have the driver stay out at least 10 laps so that the tire temperatures will be sufficient to show how they're working. Unless the car has a serious handling problem, this shouldn't be an issue. View the car from a high vantage point and note how the car looks and where the driver's hands are positioned and how far the wheels are turned while in the middle of the turns.
Testing also includes driver...
Testing also includes driver orientation to a new and different racetrack. In this aerial view of Concord, we see a strange configuration for a track that has a smaller radius in Turn 1, a reduction in banking going uphill toward Turn 2, then a dip and flatter kink going toward the backstretch. Then Turn 3 is tight with a widening radius off Turn 4. The various changes in banking cause loss in traction if not dealt with correctly with the shock settings.
Now is the time to evaluate the tire cambers, pressures, and overall handling balance. Make quick adjustments to the front tire cambers and all four tire pressures if the temperatures dictate. The handling can't be properly evaluated if these issues aren't corrected right away. Don't make chassis adjustments until the tire issues have been corrected.
Excess driver steering input at mid-turn, inability to keep the car low in the turns, and a car that snaps loose coming up off the turns are all indications of a tight setup. Have the driver run the turns at a speed lower than normal and note the position of his/her hands. Then, once the car is up to speed, the driver should again note where his hands are and if the steering is significantly different, the car is either tight or loose.
Record the driver comments as well as crew comments as to the handling and engine performance. If the car is not neutral, now is the time to make changes to improve the handling while working to maintain a balanced setup.
There's a difference between hand-ling balance and dynamic balance. The car is neutral when it's neither tight nor loose. We can easily adjust most cars so that they will be neutral. This may make the car faster, but it's not our primary goal. We need for the car to be both neutral in hand-ling and balanced in how the front suspension and rear suspension are working. When both ends of the car are working together, we'll truly have a balanced car that will be both fast and more importantly, consistent.
First We must always evaluate and correct the mid-turn performance first. To balance the car at this "steady state" point on the track will also help to balance it on entry and exit. Steady state is defined as a condition where the car is neither accelerating nor decelerating. So the dynamic effects of longitudinal weight transfer from braking or motoring off the corner aren't affecting our evaluation at this point in the test.
Before our test begins, we...
Before our test begins, we all need to meet and discuss how the test will proceed. If everyone is on the same page, the test runs smoothly and we're able to gather data that will lead to a better setup.
We can interpret the balance of the car by evaluating the tire temperatures. The easiest way to make a car handle neutral is to adjust the crossweight percent. Crossweight is the percent of the total weight of the car that is supported by the right-front and left-rear tires as read on the scales. Lowering the RF and LR corners and at the same time raising the LF and RR corners will reduce the crossweight percent and loosen the car. We always want to make changes to all four corners to effect a change in the crossweight.
Keep careful notes of the...
Keep careful notes of the test. Here, Chuck Gibson has written notes on his hand and I'm transferring them to my note pad. Any way you can record critical information is OK as long as it gets recorded and kept for future reference. I rely heavily on my notes when going over the test data later on.
After we've made the car neutral in handling, we need to make a couple of hard runs and note the tire temperatures. A car that is balanced as to the dynamics related to how the front and rear suspensions are working with or against each other will show the balance in the tire temperatures. The LF tire will be near the same temperature and working as hard as the LR tire in a balanced setup.
If the LF tire is the coolest tire on the car (by far the most common condition) then you should make changes to the setup to help heat that tire up and therefore make it work harder. With the popular Big Bar and Soft Spring (BBSS) setups, the opposite is usually true. The LR tire might be the coolest tire on the car and we need to make changes to cause the left-side tires to be the same.
Tire wear can tell us a similar story when racing on dirt. Dirt teams rarely take tire temperatures. They do feel the tires for temperature, so we know they feel it's important. But tire wear can also tell us how hard a tire is working.
Here are a few changes that help us move toward a more balanced state:
To reduce the tendency for the rear to out-roll the front (cooler LF tire)
1. Decrease the LR spring rate or increase the right rear spring rate.
2. Raise the Panhard bar.
3. Soften the RF spring rate on lower-banked tracks.
4. Stiffen the LF spring rate.
5. Move the moment center to the left.
Talk to the driver after each...
Talk to the driver after each run and ask specific questions. Have him run the lap in words and tell everything he feels and what that might mean. Back him up and expand on the questions if necessary so you can fully understand how the car is working.
To reduce the tendency for the front to out-roll the rear (as is often the case when teams try the BBSS setups)
1. Reduce the RR spring rate.
2. Raise the LR spring rate.
3. Lower the rear moment center/Panhard or J-bar.
4. Increase the size of the front sway bar (2.0-inch diameter might be a bit much--try a 1.375- or 1.500-inch diameter bar if you've been using a smaller bar).
5. Stiffen the front spring rates.
With each change, you'll need to also change the crossweight percent in order to maintain the neutral handling. The crossweight will have to increase in the first examples because as the LF tire begins to have more grip and work harder, the car will turn better and we'll need to tighten it up using a higher percent of crossweight.
In the second set of examples where the front out rolls the rear, the crossweight will need to be reduced as the rear tires develop more grip.
If your team has always used Ackermann to help the car to turn in conjunction with a tight and unbalanced setup (the LF tire runs cooler than the LR tire), then as you make changes to load the LF tire, the Ackermann will have to be reduced and/or eliminated.
A tire that is not working much (less vertical load on it) will gain traction by using Ackermann. If we load that tire, it'll really take off in the steered direction and work against the RF tire. The end result will be a severe push as the two front tires will be trying to go in different directions and both give up their grip on the track.
In our test, we were able...
In our test, we were able to view the data after each run. We looked at the shock travels, the loads on each wheel, and segment times as well as rear traction issues.
Finding the dynamic balance for the car is not the end of our goal, but is the very foundation of a good setup. It's the first and most important step in the overall setup for the purpose of getting ready to race. Small changes to the setup can now be felt by the driver as never before and we can further fine tune the setup for improved entry and exit performance.
Entry problems are almost always caused by rear alignment issues or incorrect shock rates, mostly in the RF and LR corners of the car. Make absolutely sure that the rearend is aligned properly and square to the centerline of the car. Don't take this subject lightly because you'll struggle long and hard to overcome a poorly aligned rearend to no avail. No setup change can effectively overcome an alignment problem.
Evaluate the tire temperatures...
Evaluate the tire temperatures at all times to see if the heat is distributed properly across the face of the tire. If not, make quick changes to tire pressures and/or cambers. Taking and recording tire temperature data is extremely important. The distribution of heat in the four tires tells us most of what we need to know about setup balance.
If tuning entry performance with shocks, work with compression rates in the RF and rebound rates in the LR. A RF shock that's too stiff on compression might cause a push on entry. If the RF shock is far too soft on compression, it may also develop a push due to sudden and excessive suspension movement that results in excess camber change causing the RF tire to lose grip.
Excess LR shock rebound may cause the car to be loose on entry as the weight is transferring to the front while braking. The LR shock should allow the LR tire to move in rebound to help it maintain contact with the racing surface as the car pitches forward and to the right on entry.
Spring split has an effect on entry performance too. At flatter tracks, a stiffer LF spring over the RF spring helps entry stability in most cases. A stiffer RR spring over the LR spring might feel to the driver like the rearend isn't under the car and prevent him/her from going into the corner deep enough on the banked tracks. Remember that spring changes also affect the dynamic balance of the car and you'll need to re-evaluate the tire temperatures and make changes to the Panhard bar to rebalance the setup after a spring change.
Our problems associated with corner exit involve either a tight-off or loose-off condition. If we introduce methods to gain bite off the corner, we might then end up with a car that doesn't turn well. The changes we make to improve exit performance shouldn't change the mid-turn balance. So, changes to spring rates, spring split, Panhard bar height, and crossweight will all affect and probably ruin our mid-turn balance. So, how do we tune exit performance?
The tracks where we usually see exit issues are mostly the flatter tracks with associated lack of grip. The combination of lateral forces that come from turning the car and the torque associated with power application tend to overload the grip capability of the rear tires. So we need to develop ways to increase the amount of grip the rear tires have available on exit off the corners while not affecting the mid-turn balance we have established.
We can experiment with various designs of pull bars, push rods, lift arms, and associated rear steer that happen only on acceleration. The goal is to reduce the "shock" to the rear tires upon initial application of power and increase the total rear grip level by introducing rear steer (to the left) to the rear geometry. The more the rear tires are steered, the more traction they will have, just like we've learned about the front tires associated with steering input.
There's a limit to how much rear steer we can use before the car becomes too tight. Larger amounts are tolerable on dirt than with asphalt. A few ten-thousandths of an inch of wheel movement can be felt by the driver on asphalt whereas an inch or more of wheel movement is not unheard of on dirt.
During the runs, try to observe...
During the runs, try to observe the car going through the tightest portion of the turns. Note how far the front tires are turned. Do they seem to be turned too much for the radius of the turn? Can the driver keep the car on the bottom easily or does it drift up? And, if the car looks tight, does it then go loose off the corner once the excess steering input has been applied?
At The End of The Test
Always save your sticker tires for the last runs of the day after the car is all dialed in. If the setup is good, make a qualifying run on fresh tires. After that run, do a 30- or 40-lap run on those newer tires and see if the lap times stay consistent. A truly balanced setup will provide lap times that fall off less than your competition as more and more laps are run on a single set of tires.
Review your notes when you get back to the shop and learn from both the gains and losses. All of the results are valuable and the more we learn about the effects of changes, the better we can make quick adjustments during a racing event. The top teams make a point of knowing how each chassis adjustment affects all of the other parameters involved with their setups.
Incorrect tire stagger, bent shocks, suspension binding, and poor alignment are some of the peculiarities that can ruin a test session. If radical setup changes don't seem to affect the expected result, look for a mechanical problem and fix it. Keep your test notes available for review. Test as often as you can afford and whenever the track is available. If you can plan out your goals, your performance will get better and you'll then enjoy your racing experience that much more. Good luck.