A well-handling and dynamically...
A well-handling and dynamically balanced car will gain speed in the middle of the turns and a gain of 2-3 mph is worth more in reduced lap times than if you were to add 100 hp to your powerplant in most cases. A car that isn't dynamically balanced won't handle well. Photo by Mike Horne
After all of the bits and pieces related to chassis setup have been discussed in minute detail and all of the preparation has been completed in the shop, we still have to go to the track and see how all of that worked out. Too many times, we need to make adjustments and just plain fix the handling problems that crop up. Readers have told me recently that it's now time to lay out some basic rules for tuning our race cars-so being a good listener, here you go.
The most basic rule of handling and speed for a race car lies in increasing the speed we can go through the middle of the turn. It has been said before, and rightly so, speed gained in the turns will be carried throughout the lap. This is true for both circle track racing and road racing. A car balanced for handling and dynamics is as fast as it can be.
There are other factors that will make your race car faster, but most of the gains are turn related. Given that we can all agree on the above basic principle, we further break the gain down into three turn segments-entry, mid-corner, and exit. The slowest portion of the lap is spent in the mid-turn segment, so that is where we are most interested in gaining speed.
Granted, increased average speeds in the transitions of entry and exit help reduce lap times, but the gains there pale in comparison to gains we can achieve at mid-turn. Speed gained in the middle of the turn will be carried all of the way around the track.
Remember that you need to...
Remember that you need to take care of all of the basic setup parameters before you go to the track. Items like alignment, toe settings, Ackermann, camber and caster settings, rear suspension link settings for rear steer, and more. We don't want to try to tune the setup when we have basic setup mistakes involved. We have discussed all of these in past articles. Dust off your past issues and re-acquaint yourself with those.
For a track that averages 100 mph per lap, a 2mph gain at mid-turn represents a 3/10 reduction in lap times. I've seen fast cars run up on the slower cars by 5 mph or more, and that is the half- to full-second difference between First Place and Fifteenth. So, we necessarily start out our handling tuning with the mid-turn balance, both handling and dynamic balance.
We start out solving our mid-turn handling problems. We do this because our mid-turn handling affects both entry and exit to a large extent. A car that is tight in the middle will most likely be tight into the turn and tight off. If excessively tight in the middle, the car could be loose off and here's why.
When we turn the steering wheel and cause the front wheels to create and/or increase their angle of attack, or angle differential to the direction of travel of the car relative to the racing surface, we increase the traction of those two tires. The more we turn, the more traction we get, up to a point. If the wheels are turned beyond a certain angle, the tire skids and we loose all front grip. But until then, we gain grip.
Suppose we have more rear grip overall than front grip. When we drive through the turns, with the normal steering angle that follows the radius of the turn, we will notice that the car does not want to follow the radius and instead moves up the track toward the outside of the turn. Instinctively, we will turn the steering wheel more until the car follows the radius of the track. It does that because we are causing the front tires to produce more front grip in reaction to the increased angle of attack of the front tires.
There are three turn segments...
There are three turn segments that we tune for. The place to start is in the mid-turn segment where poor handling and dynamic balance will affect the other two segments. We perfect the mid-turn and then tune the entry and exit portions in a way so as not to affect the mid-turn performance we have gained.
If our car isn't too tight, we will just roll through the turns with a slightly greater steering angle and maybe never know we are tight. But, if we are too tight, we will need to input excessive steering angle and we may just over do the adding of front grip from the increased steering angle and change from a car that is tight to one that is loose. Here is what happens.
We go into the turn and feel the tendency to not turn. We quickly apply more steering input and keep adding until the car responds. But the motion is so quick that we inadvertently over correct and add too much front grip just as we are ready to accelerate. Now with more front grip than rear, the car goes from tight to loose and with the power applied, very loose off. This is a very common occurrence.
To change mid-turn balance, we can do one of the following:
• Raise or lower the rear moment center by moving the Panhard bar or J-bar up or down. For leaf spring cars, we can raise or lower the actual spring, but that is not easy. Metric four-link cars also have a tough time changing the rear moment center height and must rely on other methods for changing the balance.
• Change rear spring rates. Softening the right rear spring, and/or stiffening the left rear spring will increase the rear roll angle and will tighten the car, as will softening both rear springs. The inverse is true, stiffening the RR spring and/or softening the LR spring will loosen the car.
The correct stagger you will...
The correct stagger you will need for a particular track is fixed and not to be used as a tuning tool. We never want to adjust stagger to mask a handling problem. Using incorrect stagger is a crutch and will only provide a temporary solution. Running the wrong stagger can cause a multitude of handling problems.
• Softening the front springs will help the car turn, but to a lesser degree than making rear spring changes. Spring split at the front also has less affect and has more influence on entry characteristics than on mid-turn. More on that later.
• Installing larger or smaller sway bars will have an effect on handling. The stiffer the bar, the less the front will want to turn. So, to help cure a tight car, we can go to a softer sway bar.
• Increase or decrease the crossweight percent. As we make changes to the crossweight, we affect the handling of the car and we can easily make the car neutral in handling by making crossweight changes. But, this is not the ideal method by any means; it's just the easiest.
• The reason this method is not ideal is because for every car and combination of springs and weight distribution, there is an ideal crossweight that matches up with a dynamically balanced setup and is related to the front-to-rear weight percentage. If we knew this magic number, we could just dial it in and then make spring or moment center changes until the car was neutral and then everything would be just right.
Rear end alignment and the...
Rear end alignment and the use of roll and squat steer can enhance exit performance. We never want to cause rear steer to the right on asphalt, but on dirt we may use rear steer to the right through mid-turn and then utilize squat steer or power-induced rear steer to the left to tighten the car off the corner.
• Increase or decrease stagger? This is never an acceptable way to tune the handling of your race car. For every turn, there is an ideal stagger that will allow the car's rear wheels to roll around the radius and not influence the direction the car travels from following that radius. Learn what stagger your track needs or use our free calculator offered on www.circletrack.com under the MultiMedia section.
Once we have set up the car to be neutral in both handling and dynamic balance, we need to evaluate the entry handling. If our entry is without issues, meaning it is straight ahead, not tight or loose, and no excess steering input is needed beyond the normal transition from straight to left turn, then we are good to go.
If all of the alignment issues have been sorted out, there should never be entry problems, but there are influences that could affect entry stability and balance. Here are the top ones to consider.
• A. Rear alignment is the number one cause of entry problems Either by misalignment of the rear tires or by rear steering of the rear end, a car can become tight or loose on entry and that can translate to mid-turn problems. The truth is, you should have checked and corrected any rear alignment problems long before you came to the track. Rear alignment and rear steer are not tuning tools.
Rear suspension links can...
Rear suspension links can be arranged to provide many different degrees of rear steer, or zero rear steer through chassis roll and squat. You can duplicate what is happening on the track by supporting the chassis on stands and then moving the rear wheels vertically and measuring the amount of movement fore and aft of each rear wheel. This is an important exercise and can help you better understand your rear end alignment issues.
• B. Shocks affect entry
Shock rates that restrict movement of one or more corners of the car can negatively affect entry. A LR tie-down shock will help cure a tight-in condition by loosening the rear, but this is only a crutch.
The two corners most affected by the dynamics of corner entry are the LR corner and the RF corner. A RF shock that is stiff on compression can cause a tight condition on entry and a LR shock that is stiff in rebound can cause a loose condition on entry.
• C. Brake bias changes affect corner entry There is an ideal brake bias that will allow maximum braking of each set of tires based on the loads those tires carry. Different cars with different centers of gravity will require different brake bias.
Tune your brakes so that wheel lockup occurs simultaneously at the two ends of the car under heavy braking. We do not want the brake bias to influence entry handling characteristics. Never try to correct a tight car by increasing the rear brake bias or fix a loose-in car by increasing front brake bias.
To test your bias settings, try this exercise. Try entering the corner with sufficient speed and with a soft application of the brakes and feel the entry balance. If good, proceed to the next step. If not, refer to steps A. through C. above. Once the car is neutral without heavy braking, then enter the corner at speed with the normal brake pressure that would be used in the race or in hot laps and see if the handling changes. If so, tune the brake bias to be neutral.
The Z-link is adjustable for...
The Z-link is adjustable for rear steer also. It is less adjustable than the four-link, but can be made to steer. Remember, when choosing spring rates in the rear that most swing arm designs where the spring is mounted on the forward link instead of on the axle tube either clamped or on a birdcage, that there is a motion ratio. The car "feels" about half the rate of the spring. The motion ratio is squared and multiplied times the spring rate to find the wheel rate. This is very important to understand.
• Setup changes to solve corner entry problems?
We never want to make changes to our spring rates, sway bars, weight distribution, or moment centers to try to solve entry problems. When we do that, we will certainly change our mid-turn handling in a negative way. We should have already tuned the car so that the mid-turn handling was balanced correctly.
There is an exception to the above rule. We can initially plan out our spring selection so that our entry transition is best for the type of track we will be running. For flatter tracks, running even spring rates across the front, or a softer RF spring rate as opposed to the LF spring rate, will help the transition into the corner. It is best to make that choice before you go to the track so you won't need to make changes after you tune the mid-turn.
Stiffer RF spring rates over the LF spring rate can help the transition into a high-banked track where the outside of the track rises up to form the high banking. In this case, the vertical forces are high at the RF on entry and we need more spring rate at that corner to control those forces to limit excessive RF wheel travel.
• Throttle modulation on entry can help solve problems with abrupt release of the throttle If we quickly jump off the throttle and into the brakes, we can upset the car to where it affects our entry speed and stability. It can also cause us to slow too quickly and attain a slower speed than is necessary to maintain through the entry portion of the turn.
This is a real phenomenon that occurs with a number of drivers. The practice of early release and later application of the brakes helps with the transition from acceleration to braking. The method is one of the primary tools taught by Mike Loescher in his driving school at Finish Line Racing-and it works. Many entry problems simply go away with an improved entry strategy.
Corner Exit Handling
Most of the time, solving the mid-turn handling will solve corner exit problems. If we were tight in the middle, we would most likely be tight off or tight/loose off. If we were loose through the middle, then we would be, well, loose off, of course.
The process of increasing mid-turn speeds means that we have also increased our exit speeds, or the speed at which we begin to accelerate. This is a big deal and the reason why we spend so much time perfecting the mid-turn balances and trying to increase speed through that portion of the turns.
The ways some tracks are laid out contribute to corner exit problems. A flat track offers less grip than a banked track because we have none of the dynamic downforce created by the banking to help provide more overall grip. So, we need to enhance bite in other ways. The transitions in the track banking angle on higher banked tracks may also contribute to exit woes.
Loose Off Condition-Rear Steer
For the left side link on...
For the left side link on a three-link rear suspension, the angle can be changed to increase or decrease the amount of rear steer as the car squats coming off the corner and while under acceleration.
To solve loose off If we know we are good through the middle, then a loose off condition can be solved with the application of rear steer that happens only upon the application of power. Basic rear steer from chassis roll does not help us because it will change our mid-turn handling.
There are ways to utilize the rotation of the rear end, if using a lift arm or pull bar, so that the motion of the rotation of the rear end causes the rear wheels to move fore and aft to create rear steer to the left to tighten the car off the corner.
Think this process out and try to arrange the components on your car to utilize this process. If definitely works. If you must run a solid third link or other type of rear suspension where the rear end can't rotate, then go to the next step.
Shock rates can increase the crossweight percent on exit to tighten your car off the corners. If you run shocks with a stiffer compression rating on the LR corner than on the RR corner, then when the shocks move as the car squats coming off the corner under acceleration and while the loads transfer to the rear, then the LR corner will carry more load and the LR and RF will then share that increased load.
A race car needs a certain...
A race car needs a certain crossweight percent based on that car's front-to-rear percent. The more rear percent, the more cross is wanted. We do not use crossweight percentage changes to alter the handling of the car. We should match the crossweight amount to the car and then adjust the setup to find the best dynamic and handling balance.
Because there is only X amount of load available, increases in that diagonal mean a tighter car. This only happens when we accelerate and the loads shift front to rear, so we tighten the car off while not affecting the mid-turn handling.
Rear spring split can also increase the crossweight percentage. This method is very "old school," but very effective. In days past, racers used to run a softer RR spring rate over the LR spring rate so that when accelerating, the LR and RF diagonal gained load and the crossweight percent increased.
Today on the same flat tracks we are talking about helping with bite off the corners, if we ran softer RR spring rates with a setup that was balanced for mid-turn dynamics and handling, we may well outrun those BBSS setups that currently use the stiffer RR spring rate.
There are many devices you...
There are many devices you can use with the rear suspension such as this double unit from Coleman Racing. The upper link controls acceleration and the lower link controls deceleration and the return of the upper link when you lift the throttle.
The only way the BBSS setups work on the flat tracks is to load up the RR corner with an unbalanced loading at mid-turn so that the RR tire drives the car off the corner. But after 20 or so laps, it is worked so hard that it gives up. The softer RR spring layout would keep biting and beat the BBSS setup in the long run.
Throttle control will allow the rear tires to maintain their grip on the track surface and help to provide better acceleration. Once we lose grip in the rear, we must back off the throttle until we regain grip before we can continue to accelerate. By exercising throttle control, we may feel like we are giving up performance, but in reality, we are providing the most acceleration possible.
Throttle control is defined as the modulation of the gas pedal through a range of motion, never moving quickly from one position to another, in order to keep the tires in contact with the track surface. The rate of change in throttle position must be altered depending on your position on the track and through the corner, so the driver must develop an educated foot.
Many drivers report that they never got past half throttle over the course of an entire race they won. This means that they were working from off throttle to half and many points in between. It is the developing of efficient throttle modulation that is one of the most effective tools you can use to promote bite off the corners.
The rubber biscuit has been...
The rubber biscuit has been around for some 10 years now and has shown to be of use if the pre-load is set fairly high. If not, the 1/4-inch plus of movement is way too much rear steer. This apparatus can be used on the right side of dirt cars with the spear rod attaches to develop rear steer that will straighten the rear end more toward square on acceleration off the corners. Dirt cars usually utilize rear steer to the right for entry and mid-turn efficiency, but need a more straight ahead position for the rear end when coming off the corners.
The above suggestions may at first seem like a bit few compared to all of what we know about chassis setup, but remember that we have supposedly already solved the critical issues facing our race car. We have aligned it, checked the moment center design, checked for binding in the suspension, rebuilt the shocks, and done all of the other maintenance things we know we should.
The last thing to do is run the car. Teams that are conscious of the effects of all of the various changes and know basically how much affect each change has on the handling of the car will go through the process fairly quickly. Three or four times out with 10-lap runs or less will be all they need to get to the sweet spot. If you're just learning these things, take good notes and concentrate on what is happening. Ask lots of questions of your driver so you can know exactly what the changes do and how much. And when you do get the car all dialed in, be sure to maintain that good setup
You Might Have A Handling Problem If...
• If you race on asphalt and you ever have to turn the steering wheel to the right, you might have a handling problem.
• If you race on dirt and you have to turn the steering wheel way to the left, you might have a handling problem.
• If you see excessive heat or wear on one tire versus the other tires, you might have a handling problem.
• If you are more than a half second slower than the fastest car on the track, you might...
• If your car starts out the race fast and then trails off, you might...
• If you get lapped in a 50-lap race, you might...
• If your driver is worn out and sweating profusely at the end of the race, you might...
• If your spotter is continually saying, "inside, inside..." and you keep getting passed, you might...
• If you have to wait longer than your competition to get back into the throttle, you might...
• If you bought that $25,000 cheater crate motor, run illegal fuel, soaked your tires, and installed traction control, and are still getting beat, yes my friend, you might just have a handling problem.