How To Improve Your Performance
It is Speedweeks again here in Florida. There has already been testing going on for the dirt races at Volusia and Bubba Raceway park as well as asphalt racing at New Smyrna Speedway. This year I will be helping an old friend, Jerry Symons get his asphalt modified up to speed for the World Series of Stock Car racing championships.
The track testing we will do in a couple of days will be a test of the changes we have already made to the car. I evaluated what the team had been doing and made suggestions for changes. Now we’ll see how those changes worked out.
During the past year, I have seen trends that disrupt the order of a balanced setup. Teams will apply methods to their cars in incomplete ways, or ways not intended for their particular type of car. One popular trend is the use of “tie-down” shocks. There is no good use for those types of shocks for the purpose of “tying” down one corner of the car.
Since the tire is not attached to the racing surface, it cannot help hold down its corner. The only thing that happens is that the shock does not allow the tire to maintain contact and loading to the track. The Tie-Down shock used on a normal spring rate will overcome that spring and lock up that corner of the car.
High rebound shocks, what some like to call tie-downs, are designed and intended for use with high spring rates to work with those rates. Bump stops and bump springs both have very high spring rates and the high rebound works with those high spring rates.
When you install those shocks on a corner with conventional spring rates, the high rebound will overcome the spring and there will be a lot of compression and little rebound. The corner jacks down and load is taken off the tires to where that tire won’t work well anymore. Be careful where you install high rebound shocks.
Goals – 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 out run the competition all the way to the last lap.
On asphalt, the setup we end up with is probably the one we will qualify and race with given small changes between the two. For dirt, we will make setup changes required for the different track conditions. That does not mean we cannot test on a track that is consistent.
A primary goal for dirt cars might be to just learn the process of making changes to meet the track conditions. There is an order and logic to adapting to changing track surface grip levels. Becoming comfortable with making those changes can be a huge performance gain.
Pre-testing Preparation / Planning – It is most important to know your car before you go to the race track for practice or testing. On Symons modified I had already evaluated the front and rear geometry, checked alignment of the car, and done a dynamic analysis of the spring combinations to balance the two suspension systems. We also looked over the dyno graphs of the shocks, checked the steering system for Ackermann, and made changes where necessary..
If you are going to a new track, take into consideration the banking and transitions. If it has a different banking angle than you are used to, a different spring setup might be in order. High banked tracks need higher spring rates overall and have little need for traction enhancing technology. If the track is flatter, include methods of creating bite off the corners into your planning.
Arrival – On arrival at the track, 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 so you can always park the car in the same position after each run.
Weigh the car before testing and after all of the testing is done at the end of the day, re-weigh the car to see how the weight distribution might have changed from the various adjustments. If the track scales are different from yours as to cross weight, note the difference and adjust what you read each time to what the shop scales read.
How to Measure Track Performance –We need to measure our on-track performance. There are two components to speed, the motor/gear, and the chassis setup combination. Since we work on these separately, we need to measure them separately.
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 how good the chassis setup is. Remember that if we can improve the mid-turn speeds, we will usually also improve the straightaway speeds.
The First Set of Runs – The driver should initially make several slower circuits and then a few faster laps 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 rear end lubricants will be brought up to temperature. We should do two more short runs following the initial outing before we can expect to get meaningful tire temperatures.
Have the driver initially run the turns at a speed lower than normal and note the position of the hands. Then once the car is up to speed, the driver should again note where the hands are and if the steering is significantly different, the car is either tight or loose.
After each run, record the tire pressures and temperatures, tire sizes, and engine water and oil temperatures. Keep hard copy records of the data in addition to digital records that may be stored in the tire temperature/pressure box or a computer.
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 are working.
Evaluation Time – 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. Do not make chassis adjustments until the tire issues have been corrected.
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 is a difference between Handling Balance and Dynamic Balance. The car is neutral when it is neither tight nor loose. We can easily adjust most cars so that they will be neutral. This may make the car faster, but it is not our primary goal. We need the car to be both neutral in handling and balanced in how the front suspension and rear suspension are working.
Mid-Turn Performance 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.
We can interpret the balance of the car by evaluating the tire temperatures. These tell us how much work each tire is doing in relation to other tires. We are looking for more equal temperatures on pairs of tires on each side of the car.
Changes to panhard bar height and/or spring rates can help bring temperature to a tire that is too cool. More uneven front tire temperatures indicate a tight car. High RR tire temps indicate a loose car. Once the tire temps come to be more equal on each side, the handling balance can be tuned with cross weight.
Remember that spring split in the rear and panhard bar height changes are the most effective way to re-balance a circle track car. As you make those changes, you might need to also tune the handling with changes in cross weight.
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 that they feel it’s important. But tire wear can also tell us how hard a tire is working.
Entry Tuning – Entry problems can be caused by rear alignment issues or incorrect shock rates, mostly in the LR corners of the car. Over-driving the entry can make a car push. Make absolutely sure that the rear end is aligned properly and square to the centerline of the car. Do not install a high rebound left rear shock. And don’t let your driver “dive bomb” the entry to the corners.
Excess LR shock rebound may cause the car to be loose on entry as load 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 some affect on entry performance too. At flatter tracks, a stiffer LF spring over the RF spring helps entry stability in most cases. Remember that spring changes also affect the Dynamic Balance of the car and you will need to re-evaluate the tire temperatures and make changes to the panhard bar to re-balance the setup after a spring change.
Exit Tuning – Problems associated with corner exit involve either a tight-off or loose-off condition. If we use the wrong methods to improve either of those, we might then end up with a car that no longer handles in the middle. So, the changes we make to improve exit performance should never change the mid-turn balance. Changes to spring rates, spring split, panhard bar height and cross weight will all affect, and probably ruin our mid-turn balance. So, just how do we tune exit performance?
The tracks where we usually see exit issues are mostly the flatter tracks with associated lack of grip or at tracks where transition in the banking cause problems. 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 while being careful not to affect the mid-turn balance we have established.
We can experiment with various designs of Pull Bars, Push Rods, Lift Arms, and rear steer that happens only on acceleration. The goals are to reduce the “shock” to the rear tires upon initial application of power and increase the total rear grip by introducing rear steer (to the left) into the rear geometry. The more the rear tires are steered, the more traction they will develop, just like the front tires when they are steered.
There is a limit to how much rear steer we can use before the car becomes too tight. Larger amounts are more tolerable on dirt than with asphalt. A few ten-thousandths of an inch of wheel movement can be felt by the driver on asphalt where-as an inch or more of wheel movement is not unheard of on dirt.
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 do not seem to provide 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 develop a comprehensive plan for your testing, your performance will get better and you will enjoy your racing experience that much more.
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