Getting The Handle

What is Handling?

How often have you heard the phrase "good handling"? While entire books have been written on the subject, three simple factors contribute to good handling. The first is making the best possible use of the tire's traction capacity. The second requires a good balance of traction front to rear. And the third factor means that the car is instantly responsive to the driver's steering, brake, and throttle inputs. Ride comfort is a consideration, but only as a secondary concern when maximum handling is sought.

Maximum traction implies sticky tires. While sticky tires provide more traction, the bigger consideration is getting each of the four tire contact patches glued as much as possible to the road surface. This combines the tire sidewall stiffness, suspension geometry, the ability of the springs and shocks to control the tires over bumps, the degree of roll resistance offered by the antiroll bars and springs, and the compliance of the suspension bushings. While sticky tires may make your car corner, brake, and accelerate faster, you are losing handling performance if those four little tire contact patches are not hooked to the road.

The second factor is handling balance. Most everyone has heard the term "push" or "loose" used in TV coverage of races. A push, or understeer, means the front tires lose traction before the rear. The car will not turn as much as it should as the limit of tire traction is reached. Ultimately, the car will continue straight ahead even with the steering turned to full lock. A loose condition, or oversteer, means the rear tires lose traction before the front tires. The car will turn more than it should as the tires reach the limits of traction. As the car oversteers, the driver must apply opposite steering to keep the car pointed in the desired direction. At the extreme, the car will spin.

The biggest influence on handling balance, that neutral point where the car does not understeer or oversteer, is the balance of roll resistance between the front springs and antiroll bar versus the rear springs and antiroll bar. If the rear antiroll bar or springs are made stiffer in a neutral-handling car, the car will become loose or oversteer. If the front springs or bars are made stiffer, the car will push or understeer. The job of aftermarket spring and antiroll manufacturers is to control body roll and create the optimum balance between front and rear roll resistance so that the handling balance is near neutral.

Many factors contribute to "good handling." A well-conceived suspension system addresses all of these factors and utilizes suspension components that are compatible for the car, the driving/road conditions, and the degree of desired handling performance. Ill-conceived systems can hurt cornering performance, provide less than optimal handling, and deteriorate ride quality. Let's take a look at the factors and components that must be right to achieve good handling.

Tire Loads

When a car is parked, a certain amount of weight rests on each tire contact patch. This static weight distribution is a factor determining the traction at each corner of the car. The traction of a tire is proportional to the weight, or load, on the tire contact patch. If load increases, traction increases; if load decreases, traction decreases. However, this relationship is non-linear, meaning the if the load is doubled on a tire, the traction is something less than double.

Weight Transfer

When a car accelerates, brakes, or corners, some portion of the weight will shift from front to rear, rear to front, or side to side. This changes the traction at each tire contact patch. For a given car and rate of acceleration, slowing or cornering, a given amount of weight willtransfer from one set of tires (front, rear, left, or right) to the opposite set of tires. In addition, there are three factors of weight transfer affecting handling: where the weight is transferred, how fast it gets there, and when it is transferred.

Weight moves from the front to the rear under acceleration, from the rear to the front under braking, and from the inside to the outside while cornering. But also while cornering, some of the weight moves from the inside front tire to the outside front tire. At the same time, weight also moves laterally in the rear. The stiffness of the springs and antiroll bars (roll resistance) determines how much weight moves to the outside front versus the outside rear. There is a delicate balance of front-to-rear spring rate and bar stiffness that creates a "neutral" handling car. Increase spring rate on either front or rear and that end will lose traction first. For example, stiffening the front springs or antiroll bars will cause more weight to transfer to the outside front and cause more understeer or push (or reduce oversteer). Changing antiroll bars and spring rates is the easiest way to control this handling balance.

Compliance in the suspension system determines how quickly weight is transferred. Suspension bushings are a small factor here, but the major control over how fast weight moves is the shock absorber. Stiffer shocks cause weight to move faster. Softer shocks cause weight to move slower. Stiffer shocks (combined with stiffer springs) reduce ride comfort. Shocks that are too stiff can cause poor tire contact patch compliance over bumpy road surfaces as well as cause the car to be too responsive. Again, the shocks must be part of an integrated suspension system designed for a specific application and set of conditions.

When weight transfer occurs it is based on when the driver uses the controls and how quickly those controls are moved. Abrupt use of the controls can cause abrupt weight transfer and upset the handling balance.

Camber

Camber is the tilt of a front tire when viewed from the front. Camber is positive if the top of the tire is tilted to the outside and negative if the tilt is to the inside. Since most front suspension systems gain positive camber during bump (compression) travel, and the outside tire goes into bump during cornering, some amount of static negative camber is needed to offset the dynamic positive camber gain and keep the tire contact patch flat on the road surface during cornering.

Camber Gain

Camber gain is caused by the front suspension geometry. During body roll the outside front tire gains camber. This tilts the tire contact patch, changes the loading across the tread, and reduces traction. Some static negative camber can compensate for this, but too much negative camber causes accelerated tire wear and can hurt straight line braking performance since the tire doesn't sit flat on the road surface. Stiffer front spring and antiroll bars reduce body roll, which reduces bump travel and camber gain. This reduces the amount of static negative camber needed to keep the tire contact patch flat on the road surface in a corner.

Toe

Toe is the angle of the front tires when viewed from above. Toe-in means the fronts of the tires are closer together than the rears of the tires. Toe-out is the opposite. Cars will turn into a corner better with a small amount of toe-out. Toe-in offers more stability in a straight line, so for highway and daily street driving, a small amount of toe-in is preferred. Too much toe-in or toe-out will increase tire wear.

Caster

Caster is the fore-and-aft angle of the spindle when viewed from the side (see illustration). More positive caster increases the self-centering effect of the steering, but also increases tire scrub slightly while cornering. Caster angles can differ from left to right and will cause the steering to pull in one direction.

Springs

The job of the springs is first to keep the car from bottoming, second to allow the tire contact patches to remain on the road surface over bumps, and finally to partially control body roll. Stiffer springs allow a car to have a lower ride height, which reduces body roll; both are important for improved handling. On the other hand, stiffer springs reduce the ability of the tire contact patch to stay on the road surface over bumps, hurting traction and increasing ride harshness. Springs must be designed as a compromise for a given set of conditions.

Antiroll Bars

Antiroll bars (also called sway bars) serve two purposes. First, they are intended to control body roll so that camber gain is not excessive. Second, the bars are a convenient way to balance the roll resistance front to rear to achieve the best handling balance. Both of these can be affected with springs, but to really control body roll with springs would require springs too stiff for either ride comfort or control over bumpy roads.

Shocks

Shocks are designed to control spring movements over bumps. Without shocks, the springs would continue to oscillate after hitting the bump, causing the car to wallow down the road. In a performance application, shocks are used to control how fast weight is transferred and thus influences the responsiveness of the car-to-driver control inputs. Shocks must be designed to work in a specific application to achieve good handling characteristics.

Tuning

Even after installing a fully integrated suspension system consisting of springs, antiroll bars, shocks, bushings, wheels, and tires, the system needs to be tuned for optimum performance. At a minimum, the proper tire pressures and suspension alignment settings must be found. Tuning can make big improvements in handling performance once you have the best components on your car. CHP