There is a correct amount...
There is a correct amount of crossweight for every combination of setup and weight distribution for your car. If your car needs 51 percent, and you run 52 or 53 percent, the car will be tight. To loosen the car, you need to lower the crossweight by taking cross or wedge out of the car. Low crossweight numbers indicate a tight setup.
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...
A car that turns well and is set up with a balanced combination of spring rates and weight distribution has a much better chance of getting more bite off the corners than one that is sideways through the middle.
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...
Some tracks have a strange transition exiting one or both turns. If the outside of the track falls on exit, the RF will follow it and take load off the RF and LR tire, making the car loose.If the inside of the track rises at the exit portion, then the LF will compress, adding load to the LF and RR and again causing the car to be loose.
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...
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.
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.