After input from the driver, a number of interacting parts deliver a turning component to the road wheels.
The basic components are:
- Steering wheel (often detachable on race cars to facilitate getting in and out of the car – particularly after a crash)
- Steering column – this steel shaft or tube will have a number of universal joints to facilitate rotation over or through bulkheads, for instance
- Steering rack – Formula One cars (and most purpose built modern race cars), use a rack and pinion system; Stock cars (NASCAR) utilize a worm gear system (the rack and pinion system offers a more precise response to steering input)
- Tie rods – these rods are connected via a multi-directional bearing to the rack at one end and to the steering plates at the other, again with a multi-directional bearing
- Steering plate or arm – this item transmits pressure to the pivoted axle or upright assembly; as one plate is pushed, its opposite component will pull
- Upper and lower pivots – the upright assembly is pivoted in two bearings (upper and lower); these bearings are often of the spherical type as they must pivot in all directions – up, down, left and right
The actual caster angle can be seen in the accompanying drawing. However, the actual angle is derived from a line drawn perpendicular to the road passing through the axle center line, and the angle of a line drawn through the top and bottom pivots. In all modern applications, the caster angle line leans away from the front of the car at its top, and is referred to as positive caster.
Optimizing the Angle
The caster angle is designed into the cars suspension/steering geometry. However, optimizing this angle is accomplished during testing. Also, each track, and even each corner, requires a different caster angle. The race engineer will decide on the best compromise.
Not all race cars have the same caster angles on each side of the car. This is known as caster split. All circle track cars carry a different caster angle on the left front to that of the right front. The reason for this is that the radius followed by the outer wheel is greater than that of the inner wheel; hence a different steering angle is required.
For long fast corners (such as those at the Indianapolis Motor Speedway) the caster angle will be toward the highest settings to give a slow response and to enhance the self centering effect this offers.
Self Centering Effect
For tracks such as a street circuit (Toyota Grand Prix of Long Beach or Monaco, for instance), the caster angle will be much less as the car will be required to change direction quickly; the self centering effect being of less importance than the ability to change direction.
 |
 |
 |
 |
 |
