There are many names for the condition in which a race car turns too little or too much. So let's start with some definitions.
"Push," or "understeer," means the car doesn't want to follow its steered direction. Therefore, it is said to be pushing away from the steered direction. The opposite of a push is when the car's front tires stick to the track and go in the steered direction.
"Oversteer" is another name for "loose." Loose is the term for the rear end wanting to pull around and turn the car sideways in a corner. The opposite of loose is "tight." Tight refers to having the rear of the race car sticking too tightly to the tracks made by the front.
PushFirst, let's tackle push. When a race car enters a corner, the steering wheel is turned in the direction the driver wants to go. If the traction available is sufficient, the front end is said to stick. Thus, the front end of the car follows the steered direction.
When the front tires do not have enough traction to overcome the straight-line inertia of the car, they skid across the track. The tires are pointing into the turn but the car is in less of a turn. Here the car may turn somewhat but not enough to negotiate the turn quickly.
A push on corner entry is much the same as applying the brakes-the tires are sliding. The immediate cure for this is to slow the car until traction overcomes inertia. Now the car will follow the steered direction, but speed has been lost.
The simple cure for a push is to add weight to the right front, creating more traction. There are many things that contribute to front traction: springs, shocks, caster, camber, to name a few. However, given that the rest of the suspension is somewhat close to correct, weight must be added to the right front.
I am not suggesting 11/42-inch thick lead fenders. The weight must be shifted from one corner to another. To do this, the right front will be raised in comparison to the left. If the car has weight jacks, then simply screw down on the jack. Keep doing so until the push goes away. Without weight jacks, use a smaller left front tire or larger right front. Keep in mind, there can be too much of a good thing. Every adjustment on a race car is a compromise.
I have often seen a push misdiagnosed. In a severe case, the car pushes, slows down and grabs a handful of traction. When power is applied, the rear spins around and the driver is looking at where he has been. Often the driver says the car is loose.
Corner problems must be solved in the order in which they are received. In other words, a problem on corner exit cannot be solved until any problem on corner entry is corrected. In the preceding example, the problem was not the car wanting to spin out. Instead it was the push that led to spin out.
Push can also be a problem on corner exit. Here, with power on, the car drives outward toward the wall. Right-front weight will have little effect in this case. In this scenario, the push is caused by the rear of the car. The rear, with power, has more traction than the front, so the rear wheels direct the car. When the right-rear tire is larger than the left, it is called "stagger." Add stagger, i.e. a smaller left rear, when the rear drives the car toward the wall on corner exit.
This difference creates a tendency for the rear to turn. The classic example is the foam coffee cup. It has a larger diameter on one end and a smaller on the other. Laid on its side and given a shove, it will roll in a circle. This is how rear tire stagger works.
Loose, TightSimply stated, loose is the condition where the rear wants to run outside the tracks of the front. In a severe loose condition, the car will spin out easily. Conversely, a small amount of loose is often beneficial to speed. This allows a driver to balance power and traction with his throttle foot. This is especially true on dirt.
To easily understand the term loose, push a small toy car with a pencil and make it turn a corner. It turned sideways very easily because it is loose.
A car can be loose on corner entry. Braking or slowing will tend to make it go sideways. This means the car must be slowed to a greater extent to enter the corner safely. Stagger has little effect with the power off. Corner entry speed is critical. It sets the speed for the rest of the corner. If the car is too loose or has a push entering a corner, the resulting need to slow down will make the speed on the next straight slower, too.
The first thing this car needs is to be tightened up on corner entry. We can dial in some right-rear weight with a jack screw. Remember, it is all a compromise. It is possible to get the car jacked all out of shape, so go easy. Note how many turns up or down are made so you can return to the original settings if needed.
Other things affecting a loose-on-entry condition are brakes and springs. If the rear has too much braking force over the front this can be a problem. If you have an adjustable brake bias setup, then dial in more front brakes. The rear tires here are using their traction to slow down, thus their sideways traction is limited. If the right rear spring is too strong, the chassis won't roll over and transfer weight to the right rear. Excess wheel offset can cause the problem too. Tucking the wheel back closer to the chassis has the effect of adding weight to that corner.
If the car is loose on corner exit we have another set of circumstances. In this case, when power is applied, the car wants to go sideways. A small amount of this is beneficial. Theoretically, a neutral-handling car would be best. But the track is never the same in any two corners, much less from hour to hour. Remember, a push scrubs off speed but a bit of loose lets a driver drive with the throttle, power on.
The easiest way to make changes to a loose-coming-out condition is with stagger. Too much stagger causes the right rear to swing around. Zero stagger tends to drive the car the way it was pointed when the power was applied. This happens whether you are out of the corner or not. The right amount of stagger for the moment allows all the power to be applied and the car to be kept under control. Sometimes you will need to change stagger several times throughout the race program as the track changes.
I have run across a few occasions where a driver has used reverse stagger (larger on the left). His car worked OK, but I believe some other part of the suspension was crippled and this was a patch. A man can run pretty well on crutches if he has enough practice.
Some classes, notably IMCA cars, use the same tire on all four corners. There is a size difference, but it is only slight. Here, things other than stagger must be used to loosen up the car. The right-rear spring can be lighter than the left. Thus, the car rolls over due to centrifugal force and loads the right-rear tire. Since it is the outside tire in the turn, it will have more traction than the left, where the weight is being unloaded. This pulls the rear of the car to the right. Wheel offsets can have some effect on this, too. In classes where it is allowed, suspension modifications play a large part in loosening the car up.
SummaryTo be fast, a race car must be balanced at the right point between push and loose. Imagine this point to be in an envelope: The better the driver, the larger the envelope can be, without affecting the speed of the car. It is difficult to achieve this balance consistently. Also there is no perfect setup that works all the time. A car that is right for the moment makes a driver look good.
Trouble In Aisle 2!A shopping cart experiment gives you an idea of loose and tight.
Welcome to Sleepy's Grocery Cart Driving School. This may sound odd, but the results are real. You can get the feel for the way a race car handles by going around corners at the supermarket.
First, select a grocery cart that rolls straight and smooth. Your first exercise is to learn to drive the cart with only your fingers on the far outer ends of the handle. Using the thumb and forefinger only lets you feel the handling changes we will be making.
Swing over to the beverage department and pick up three 12-packs of canned drinks. The placement of these will be the adjustments used to change the handling. Next, find a short island, preferably not in the busiest area of the store. Here you can take as many laps as you need to complete your lessons.
Begin by placing all three "weights" across the front of the cart. Walk briskly, but don't run. Begin your approach toward the end of the straight by positioning your cart in the middle of the aisle. Start your turn by pulling on the left corner and pushing on the right. You will find the cart has a push. The front will not want to turn the corner.
When you slow down, you will need to push the handle to the right. Now, your control will be more effective. Finally, the front will begin to turn while the lightly loaded rear will easily slide sideways. Accelerating out of the corner, the rear will be loose. Meaning, if you continue pushing hard while finishing the turn, the cart will spin out.
What you have encountered is the classic push-in/loose-out syndrome. The car has a push and goes to the outer edge of the track. It slows, the front catches, the rear comes around and the car drives down across the track. Beginning drivers often misdiagnose this condition as being loose.
Moving the weights to the rear has a somewhat opposite effect. Your fingers will have good leverage over the light front end. At the end of your straight, it will be easy to make the cart turn left. However, on corner exit, when you pick up some speed and try to maintain the turn, there will be a different situation. At this point, the cart will be trying to make the turn wider, perhaps wider than the aisle unless you slow down. This is called a "push on corner exit." On a real race car, rear tire stagger (larger right rear) can often cure the problem.
Next, move the three weights to the center of the left side of the cart. This will result in the corner entry and exit being controllable while still carrying a good speed. This is the ideal cornering handling situation. It is seldom achieved consistently under racing conditions.
Try moving the weights to the right side while still making your left corners. When the cart feels like tipping over you will understand why left-side weight makes a car fast.
Though these examples of handling may be exaggerated, you can get the feel of what a race car driver experiences.