How to Fix a Race Car That Won’t Handle Correctly

Oh Behave!

Today, most teams are focused on the setup du jour with bump setups on asphalt and softer, less aggressive setups on dirt. With all of this attention on the springs, gadgets, and overall attitude of the car, we sometimes get away from the basics and get lost in the trees. It may be time to step back from the forest and look at the big picture. We can still have our modern setups, we just need to make sure the all important basics are not askew.

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.

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.

Mid-Turn

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 lose 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.

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 overdo 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 changes from tight to loose and with the power applied, to 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.

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 cross weight percent. As we make changes to the cross weight, we affect the handling of the car and we can easily make the car neutral in handling by making cross weight changes. But, this is not the ideal method by any means, it is 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 cross weight that matches up with a dynamically balanced setup. The correct amount of cross weight is directly 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.

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.

Speed gained in the middle of the turn will be carried all of the way around the track.

Entry Problems

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.

Rear alignment is the number one cause of entry problems. Either by misalignment of the rear tires or by rear steering of the rearend. 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.

Shocks affect entry. Shock rates that restrict movement of one or more corners of the car can negatively affect entry. An 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. An RF shock that is stiff on compression can cause a tight condition on entry and an LR shock that is stiff in rebound can cause a loose condition on entry.

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.

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 through the entry portion of the turn.

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 way that some tracks are laid out contributes 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 improve 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 can be used 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 several ways to mechanically cause the rearend to steer only when we accelerate. We have experimented with some of those methods with our project cars and reported the results in previous articles. It might help you to look those up.

Shock rates can increase the cross weight 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.

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.

Conclusion

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 they affect the car. And when you do get the car all dialed in, be sure to maintain that good setup.