September 11, 2002

How control bars affect handling

When I am out the track with the local sports car club, I am often asked how to make a car handle better. You can have all the horsepower in the world, but if the suspension isn't up to snuff, horsepower is useless. Techniques used to make race cars handle better also can make street vehicles more stable and safer.

Springs are usually the topic of conversation, but control bars are often the difference between good handling vehicles and those that tend to "fall over". Both sway bars and panhard bars are used for suspension control, but the purpose of each is often confusing. They are used for entirely different purposes.

Panhard bars are used to help locate a solid rear axle under a vehicle. The bar is mounted across the vehicle, with one end connected to the rear axle housing and the other end connected to the body. During cornering or sideways movements of the vehicle, the bar keeps the axle located laterally under the body. Panhard bars should be as long as possible for the best handling.

Independent rear suspensions do not need a lateral bar to hold the axle in place, and some vehicles with solid rear axles do not use a panhard bar. The rear axle may be held in the proper location by leaf springs, control arms mounted at a V-shaped angle, or even a Watts linkage. The Watts linkage is a type of panhard bar but it uses a swivel linkage in the middle to reduce the body lift effects that a panhard bar has during hard cornering.

Sway bars are used to reduce body roll or lean during cornering. Almost all vehicles are equipped with a front sway bar, and many performance vehicles have a rear sway bar too. Sway bars are wide U-shaped bars with the bottom of the U often mounted to the body with bushings and the arms of the U mounted with links to the suspension. When a wheel moves up on one side of the vehicle, the spring steel sway bar lifts the wheel on the other side of the vehicle. The added weight on the other wheel keeps the vehicle body relatively flat, making the suspension angles better for higher traction.

There is a lot of science to sway bar selection. The strength of the bar must be matched to the weight and size of the vehicle. Professional racers will use different size bars to help tune the suspension. An increase in sway bar diameter of even a few thousandths of an inch will make the bar significantly stiffer. Some bars are hollow tubes, while others are solid steel. The length of the arms on the sway bar also make a difference. Short arms have less leverage, so the bar is stiffer. Some aftermarket sway bars have adjustable positions for the connecting links at the ends of the bar to adjust bar strength.

Adding a rear sway bar from another car to yours may be simple, but if the front and rear are not compatible, you will have different traction at the front and rear. This can make the car swap ends very quickly. When installing a sway bar, use both the front and rear bars from a high performance version of the same model car, or select a set from aftermarket suppliers. They have already done all the research to make your vehicle better handling

Sway bars are not just for high performance vehicles. Top heavy vehicles can benefit too. Motorhomes, vans, and even work trucks may benefit from the decreased body roll that sway bars can provide. One aftermarket version of the sway bar for motorhomes uses hydraulics instead of spring steel. A double action hydraulic cylinder is mounted between the body and the rear axle on each side of the vehicle. Connecting hoses transfer oil from one cylinder to the other in an opposite direction. If the body leans and one cylinder extends, the hydraulics cause the other cylinder to extend, reducing the body roll.

Many performance enthusiasts believe that stiffer springs will make the car handle better. They will reduce body roll, but give a harsh ride and make wheels and tires bounce off the ground more. Traction is actually decreased! Good handling cars use soft springs, and use premium quality shock absorbers and sway bars to keep the body flat and the tires on the road.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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