Roll bars are used for fine tuning the balance of grip created by the roll of the vehicle. There are a few different types of roll systems in use.

Touring Car - Tortion Bar (Road Car, Nascar):

Touring car or road car roll bars are the simplest form of roll system. The system usually consisting of one bar at some diameter that connects to both the left and right suspension arms. When the suspension raises or lowers equally on each side the bar has no effect on the suspension of the vehicle. When the car rolls into a corner the bar has two effects the first effect is that the suspension gets a little harder on the outside of the vehicle due to the torsion affect of the bar. The second effect is that the bar will lift the inside tire off the ground which will level out the car and reduce the pressure placed on the outer tire. The leveling effect is what makes this system work.

This system works on the premise of reducing grip forces to equalize the balance of a vehicle. Due to the reduction of grip philosophy the use of this system can be out of place and cause more reductions than gains. The biggest gain that this system can make is to keep all four wheels on the ground.

When the suspension is set soft while cornering a vehicle will have the tendency to dive under heavy braking and or squat under hard acceleration. When the car dives under braking it can lift up the rear inside tire. This lifting of the tire is reducing a whole tire worth of grip through cornering. To get that tire back on the ground would be a big gain. To do this you would use a front anti roll bar. Using the front anti-roll bar to fix the problem on the rear works because of the nature of the system. Since the roll system lifts the inner tire to correct the roll of the car it also sets the rear inside tire closer to the ground or adds pressure at the rear. If the front roll bar lifts the inside tire enough (reduces outer front grip and roll) the inside rear tire will be placed back on the ground. Hard acceleration in a corner can have the same effect as hard braking but the exact opposite. The front tire will lift instead of the rear, putting a rear roll bar will correct this.

Once the larger problem of tire lifting is solved then you use the roll bars on the front and rear to achieve the correct roll to provide the optimum pressure to the tires that are being used. You can however limit the roll to much and this will reduce grip on the tires taking you out of the optimum settings. This type of roll system affects the ride height of the vehicle so compensations may have to be made in the straight line set-up to compensate.
Tire pressure will further be explained in the sections of suspension geometry and tires.

Drawing showing the placement of the Anti-roll System to come.

Torsion Roll System (independent):

This system is commonly found on cars with a laydown or pushrod type suspension system. It connects to the bell cranks of the suspension one rod for each side of the vehicle. These rods run parallel and are then connected to a single pivot that is connected to the torsion bar that controls the roll. As you can see the system on this type of car and suspension is much more complicated than that which is found on a normal road or touring car .

The added complication of this system does have an advantage. This advantage is that it allows the vehicle to have a stiffer roll characteristic that is completely Isolated from the main set-up of a vehicle. This will allow changes to be made in the roll of the vehicle that will not affect the set-up for the straight or the ride height of the vehicle. This system because of itıs isolation can be adjusted separately and actively while the vehicle is running. This cannot be accomplished with the use of a normal roll bar.

The one downside is that the roll of the vehicle is now being controlled by the torsion of the bar. Torsion bars can fatigue and become inconsistent through itıs range of motion. This fatigue causes the bar to have to be changed frequently to keep a consistent set-up.

Drawing showing the linkage of the Torsion roll System to come.

Proportional Roll System (independent):

This system is an advancement on the torsion roll system. The linkage of the system is effectively the same with one major difference. The difference is that the torsion bar has been replace with another set of linkage that is connected to a spring system. These springs are what now control the roll of the vehicle. Since it is now a spring controlled system you have all of the adjustments that you have for the normal suspension including dampening if wanted. This roll system added on top of the existing suspension gives the benefits of being able to control the speed, angle, and stiffness of the roll without affecting the same variables in a straight line.

The proportional system is much like having two complete suspension systems on the vehicle that will alternately switch to handle the parts of handling that they cover best.

Drawing showing the added systems of the proportional roll System to come.

Active Suspension (fully independent):

Active suspension is a completely computer controlled system that will adjust shock dampening and spring rate with the use of hydraulics in a split second. This makes real tuning as far as the suspension dampening virtually unnecessary. You need to be more of a computer programmer at this point. The advantages to this system a immeasurable since they are so great. You have no compromise in the shock and spring set-up since it is completely variable by the computer. The dampening tuning has become foolproof at this point.


İ1997 Penguinr/c