In order to have the perfect exit, the entry and middle need to be correct. We want the ca
In this age of improved engine systems that help us gain more horsepower and torque, what remains as one of the greatest challenges in circle track racing is the issue of handling. It is a generally accepted truth that speed gained in the turns is much more significant than any small legal gain in engine power.
Speed gained in the turns will be carried all the way around the racetrack. If you can gain 1 mph in each of the turns, then you will have gained 1 mph on the straights, too. That 1 mph equals a reduction in lap times of 111/42 tenths for a 16-second-per-lap track with an average speed of 100 mph. For most tracks and series, that represents the difference between the pole and Tenth Place in qualifying.
With the car already loose, the application of power increases the problem. In testing, we
In Part One of this two-part series, we examined how to recognize basic handling problems and ways to correct them for corner entry and the middle of the turn. We believe that midturn balance is most important to overall handling performance. Entry and exit performance is also very important for both performance and the ability to race other cars and move forward through the field, even if that means passing lapped traffic. We have worked on midturn and entry problems. Now let's tackle the exit problems.
Loose on Exit Being loose off the corner is possibly the most detrimental handling problem we can have in an actual race. Many passes occur as the cars are exiting a turn. Other racers can recognize when you are having problems with bite off the corner and set you up by laying back a bit and making a run off the corners. You are forced high coming out and must steer more to avoid the wall. With a car that is already loose, that means backing off and letting the passing car go. This will happen with many more cars until one comes along that is as loose off as yours.
A car that is loose on exit could have several problems. When we race on asphalt, this condition usually occurs on flatter racetracks and on tracks with worn surfaces. Some of these problems/fixes relate to both dirt and asphalt, but some will not cover both.
There is a design for a three-link rear end that utilizes a lift arm or pullbar where the
1 Shock Compression and Rebound Rates
If the LR shock is too soft on compression or the RR shock is too stiff on compression, the car will lose some amount of crossweight percentage momentarily as we get back into the throttle and load transfers to the back of the car. With that, the rear of the car and the rear shocks compress and the front shocks rebound. To gain bite off the corners, the LR shock should be at a higher rating for compression than the RR shock. This serves to increase the crossweight momentarily as the car accelerates and the rear of the car squats.
Front rebound rates affect the distribution of weight also. Many teams will decrease the rebound rate of the LF shock to loosen a tight car off the corners. This could be making your car too loose off. Match the front rebound rates if a split is making the car loose.
2Rear Spring Rates
The combination of rear spring rates can affect the amount of traction we have on exit at the rear of the car. This could be especially significant with the asphalt big bar and soft spring setups. With the BBSS springs, the RR spring is usually much stiffer than the LR spring. As load transfers to the rear upon acceleration, the LR spring compresses more than the RR spring, and that de-wedges the car. To compensate for this, the LR shock should have a much greater compression rate than the RR shock.
Basic shock tech tells us we need more compression control for a soft spring, because the spring resists compression, too, and there is less spring to resist. For stiffer springs, we need much less compression because that stiff spring will resist compression so well.
The angle of the rear trailing arms is critical in determining the degree of rear steer yo
For conventional setups, keep the rear springs even in rates or use a slightly softer RR spring if traction is needed. Whichever setup combination you choose, make sure the setup is balanced and that changes to the spring rates are in conjunction with corresponding changes to the Panhard bar height to maintain a balanced setup.
The amount of rear spring split (RR softer than the LR) needed varies with the type of car. A coilover asphalt Late Model car only needs about 10 or 15 pounds of split to get the job done. A dirt LM could use a 50- or 75-pound split to cause the car to roll over more dramatically with dry-slick conditions in order to create a sufficient amount of rear suspension movement to promote the rear steer that is needed for those conditions.
A stock car with the metric four-link rear suspension and big springs mounted in the stock location needs more split of up to 50 pounds of difference in order to overcome the high rear moment center that is associated with that type of suspension.
3 Rear Steer
Your car could develop a loose condition if the rear suspension is designed to steer to the right as the car rolls and squats on exit under full acceleration. The suspension links may produce zero steer under normal cornering attitudes associated with rolling and diving. That may change as the car squats after weight has transferred when the car accelerates so that the new arm angles now produce rear steer to the right.
The LR trailing arm has a significant effect on rear steer associated with excess squattin
Adjust the angles of the rear control arms so that you will have near zero rear steer when the car is at the exit attitude. An increase in the amount of antisquat also serves to limit the amount of rear suspension movement while the car is accelerating, which reduces the effect of rear steer. This effect can be mistaken for added bite. In reality, it reduces unwanted rear steer to the right, fixing a loose-off condition.
4 Mechanical Traction Control
If the car is good through the middle and initial exit but loose off the corner as we get into the gas, then the problem might be one of power-induced wheelspin and we need to further develop our traction-enhancing program. The primary goal is to eliminate the "shock" that reaches the rear tires due to engine torque that comes from initial application of power. We can utilize systems that increase the crossweight and those that produce rear steer to the left to help tighten a loose-off car.
The cars with the metric four-link rear suspensions can benefit from mechanical traction control, too. I have heard of teams utilizing more solid bushings in the left-side connections at the chassis and the rear end, but leaving the stock rubber bushings in the right side. This provides less rear steer in the middle of the turns but introduces rear steer to the left upon acceleration as the right-side bushings compress.
5Weight Distribution and Placement
If we feel comfortable with the balance of the car related to the geometry of the front and rear ends, then we might be set up a little too loose with the crossweight percentage. The car might be able to handle more crossweight and still turn fine through the middle of the corner as long as the front geometry is correct. A car that is more "free" feels really nice through the middle, turning with almost no effort, but we need a slight amount of "tight" to assist our exit performance.
One driver I used to work with (who had won several championships) always drove faster, especially during the race, if the car was a little tight in the middle. He would say after a practice run, "She's pretty good, just a touch tight in the middle." When I would take that "touch" out of the car, he would slow down by 2-3 tenths.
The pullbar is just one device that racers use to reduce the "shocking" effect at the rear
A driver must feel that the rear of the car is under him or her to feel more confident pushing the speeds in the turns and taking the car to the limits when passing other cars or holding off a challenge. That is exactly why the front geometry needs to be correct so that when we need to turn the car against a tighter setup, it goes where we point it.
6 Tight/Loose Syndrome
The limit to what was discussed above is when we set up the car to be too tight. We have learned that a tire will actually gain traction as we increase the angle of attack, or in more simple terms, when we increase steering wheel input. That means if we have a tight car in the middle of the turns, we can compensate by increasing the steering input and the front will gain traction to match the rear.
The problem with this is what we call the tight/loose syndrome. When the car is set up too tight, we can still possibly overcome that with even more steering input, but at some point, and this happens very quickly, the balance is reversed and the front ends up with more traction than the rear.
This almost always occurs just about the time when we are getting back into the throttle. So the car is already going loose, and then bam-we gas it up and then the car really goes loose. The driver comes in and swears that the car is loose, but if we can recognize the tightness in the middle, evidenced by the amount of steering input, then we will know the difference and be able to apply the correct fix, which is to loosen the car for a more balanced midturn.
There is a correct amount of crossweight for every combination of setup and weight distrib
7 Sway Bar Preload
One effect that tightens a car that is loose off the corner is sway bar preload. It has been demonstrated many times that we can help provide more traction off the corners by adding preload to the sway bar. A caution here is in order. If we know the correct crossweight that the car needs for midturn performance, then we need to weigh the car after we preload the sway bar. Adding preload, especially when using a larger-diameter bar, really adds to the crossweight percentage.
For the larger sway bar setups, preload is not an option. I have seen teams try to preload a large sway bar only to see the ride heights change dramatically. I watched one team fight the ride heights for over a half-hour. You cannot preload a 111/42-inch or larger sway bar.
8 Racetrack Transition
The shape of the racetrack can affect how the car is balanced when exiting the turns. If the transition is abrupt and the top of the track drops to match the inside edge elevation going into the straightaways, then the RF will follow the drop-off and unload the LR wheel. Shock rebound rates need to be adjusted to allow the LR tire to stay in contact with the racing surface.
If the LR shock has too much rebound, then that tire will lose a lot of load and not be able to provide traction. The RR tire will be the only one trying to accelerate and turn the car, and it will run out of traction and spin. Decrease the amount of rebound in the LR shock and/or soften the rebound in the RF shock to help this situation.
A car that turns well and is set up with a balanced combination of spring rates and weight
9Excess Rear Stagger
Every race car needs a certain amount of tire stagger (tire size difference in the rear tires to compensate for the turn radius so the rear-wheel rpm will be equal at midturn) and no more or less. Excess stagger should never be used as a crutch to help make the car turn in the middle or while under power if it is tight. Doing this will probably make the car loose off the turns while under power.
Stagger only affects midturn handling if the car has a spool type of rear differential or a Posi-traction type of rear differential. With a Detroit Locker, one or both of the axles will be unlocked going in and through the middle and lock back up on exit while under power. So, with the DL style of rearend, stagger should match the radius of the turn where the car is starting to accelerate.
Tight Off the Corner
Many racers could say they wished they had this problem, but nonetheless, it does exist. This condition is many times tied to a geometry problem or possibly a shock package mismatch. It hurts our performance because as we accelerate off the corner, we might need to eventually lift to avoid the outside wall if the push is severe enough.
If we are racing someone and get under them coming out of the turns, we would most likely be forced to lift to avoid pushing into the outside car. Many cars have been taken out because the inside car did not lift when they should have. Here are some common reasons why the car might be tight on exit off the corners.
1 Front Shock Compression Rates
If the RF shock is too stiff on rebound or the LR shock is too soft on compression, the RF corner of the car will lose weight as the car accelerates, causing the LR to also lose weight. The result is more weight distributed to the LF and RR, which reduces the crossweight. This will obviously make the car loose initially as the car starts to accelerate.
Some tracks have a strange transition exiting one or both turns. If the outside of the tra
2 Rear Spring Rates
The rear spring rate combination could make the car tight off the corners. Excess rear spring rate split, with the RR spring rate less than the LR spring rate, would make the car very tight off the corner while under power.
In most cases, reduce the spring split until the desired effect is less than needed and go back up to the next level. If you have a 25-pound split in the rear springs, try a 15-pound split. If that produces enough bite, leave it there. The car must be neutral off the corners so that we can maneuver around other cars in the race.
3 Rear Steer
A small adjustment to the geometry of the rear suspension can reduce the degree of rear steer to make the car more neutral while under power. If the car squats as power is applied, then it is possible that the added movement is making too much rear steer to the left, which tightens the car considerably.
With three-link rear suspensions, the arms are fairly short and a height difference at the front of the arms of a quarter of an inch can be felt by the driver. A half-inch change can make the car undrivable. Make height changes to your trailing arms in small increments.
4 Front Wheel Camber Change
If the front of the car rises as we get back into the throttle, it is possible that this movement will cause the front wheels to change camber quickly and lose traction on initial application of power.
The rear stagger should be matched to the racetrack and not used to correct handling probl
In a test session we were running at Concord Speedway in North Carolina a few years ago, the car was developing a slight push just as the driver was accelerating off the corner. We could see the front end rise, evidenced by the increase in the gap between the top of the left-front tire and the top of the wheelwell. We pulled the front shocks and increased the rebound rates in both front shocks. That solved the problem. Since we maintained the rebound split between the shocks, we determined that it was the sudden change in the camber of the front wheels that caused the front of the car to lose grip.
5 Rear Stagger
If we do not run a sufficient amount of rear stagger for the radius of the turns, especially where the car is initially accelerating, then the rear end will drive the car to the right. I have known teams who had otherwise nicely balanced race cars that could not get off the turns without heading for the outside wall.
Running less stagger than required for the track banking angle and radius will make the car tight on exit, driving the front toward the wall. In a recent exchange with a team, it was discovered that they were running only about 31/44 to 1 inch of stagger when the track they were running at required 2 to 211/44 inches of stagger. Obviously, their problem was a car that was tight off the corners.
We have discussed and given advice about rear stagger and what the car wants at various types of racetracks in CT. Use those guides and do not tune the car's handling with stagger. Give it what it wants and some of your exit problems will go away.
Conclusion When attempting to tune your car's handling balance at the racetrack, always start with the middle phase of the turns. Run the car at a moderate speed through the middle, well below race speed, and note how far the steering wheel is turned. Speed up and do a few hot laps and again note the position of the steering wheel. If the wheel is turned farther at speed, the car is tight; if it is turned less, it is loose. If you have to steer to the right at midturn, bring the car back in. That simple test has helped many teams quickly determine the status of their setups so they will quickly know which direction to go when tuning the midturn handling.
Next, tune the entry balance and then tune the exit balance. When all three phases are balanced, work on driver finesse and practice passing maneuvers running high and low off the corners. With the car set up correctly, it is just a matter of experience and a little racing luck that brings that first win.
The rear stagger should be matched to the racetrack and not used to correct handling problems. A racetrack will require a certain amount of rear stagger, depending on the radius of the turns and the banking angle. The track turn radius you will use to determine the correct stagger matters the most where the car will be accelerating. The accelerating-portion radius (exiting one-third of the turn) might be larger than the midturn radius. With cars that use the Detroit locker rear differentials, less stagger should be used than would be dictated by the middle radius so that both rear wheels are turning the same rpm off the corner.
The front mounting bracket on a three-link rear suspension is adjustable to allow the team to change the angle of the trailing arm. The driver can feel small changes to the height of the front of the trailing arm.
A "pushrod" trailing arm installed on the right side will compress when the car is accelerating. This shortens the link and allows the rear end to steer to the left, which tightens the car considerably. Most teams who find this useful always find it necessary to tighten the preload on the rubber biscuit to limit the amount of movement. Small amounts of rear steer go a long way toward tightening the car off the corner.