TYRES and SUSPENSION: CAMBER
What is the camber angle and its impact on vehicle dynamics
The camber is the measure of the angle between the vertical axis of the vehicle and the centerline of the wheel, observing the vehicle in front to rear. As we see in the picture, if the wheels have the upper part inclined towards the outside of the car (the top of the wheel is farther out than the bottom), the camber is said to be positive, inward it is said to be negative (the bottom of the wheel is farther out than the top), while the absence of inclination indicates a neutral camber – zero camber.
The modification of this angle varies the position of the wheel with respect to the contact road surface so that, under load transfer conditions (for example in the presence of lateral acceleration during a curve), the inclination of the vehicle bring the contact surface of the wheel itself to be as parallel as possible to the ground, so that the tire offers the maximum support surface in this situation, therefore the maximum grip or handling. In fact, the ideal situation would be obtained if the tire always remained perpendicular to the ground without deforming in the presence of high lateral loads, in other words transmitting the forces through the vertical plane of the tire rather than through a shear force across it.
So we understood as the camber angle alters the handling qualities of the vehicle; in particular, negative camber improves grip when cornering.
This effect is compensated maximizing the contact patch area. Note that this is only true for the outside tire during the turn; the inside tire would benefit most from positive camber.
As we’ll see in the following chapter, caster angle will compensate this to a degree, as the top of the outside tire will tilt slightly inward and the inner tire will respectively tilt outward.
Camber: the impact on vehicle dynamics.
On the other hand, for maximum straight-line acceleration, the greatest traction will be attained when the camber angle is zero and the tread is flat on the road. Proper management of camber angle is a major factor in suspension design, and must incorporate not only idealized geometric models, but also real-life behavior of the components; flex, distortion, elasticity, etc. What was once an art has now become much more scientific with the use of computers, which can optimize all of the variables mathematically instead of relying on the designer’s intuitive feel and experience. As a result, the handling of even low-priced automobiles has improved dramatically.
Optimal camber, especially in race cars, depends on temperature, tire pressure, track conditions and one of the most important things is the compound of the tires and the stiffness of the side wall that underline the range of possible inclinations. Excessive camber angle can lead to increased tire wear and impaired handling, side-walls also may not support the loads.
A great percentage of road cars have positive or zero camber in order to due to the profile of the road (convex track).
On the rear wheel drive there is frequently an important negative camber which aims to improve the stability of the vehicle.
Off-road vehicles such as agricultural tractors generally use positive camber as well. In such vehicles, the positive camber angle helps achieve a lower steering effort. Also, some single-engined general aviation aircraft that are primarily meant to operate from unimproved surfaces have their taildragger gear’s main wheels equipped with positive-cambered main wheels to better handle the deflection of the landing gear.
A car with very soft suspension requires a more pronounced negative camber angle than one with very stiff suspension.
Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer’s efforts.
In race cars camber is adjusted through adding or removing shims from one of the arms of the suspension system or with threaded rods.
With the change of the camber, we have to pay attention to the ride height of the car.
As we incline the wheels (negative or positive), as the height of the cars decreases.
For competitions, it’s necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results.
The Optimal Camber Angle.
After the feeling and the feedback of the driver, the best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it’s desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it’s far more important to ensure that the tire is up to its proper operating temperature than it is to have an “ideal” temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature.
The camber is one of the easiest changes to reduce understeer and oversteer phenomena.
Increasing the negative front camber, we increase the front stability of the car going toward an oversteer behavior of the car, on the other hands increasing the negative rear camber it’s more difficult to rotate the back of the car and we’ll suffer more of an understeer car.
The camber angle must be adjusted (whenever possible) in relation to the speed of the curves or to be precise when the car rolls; in fast curves (high roll) you need a very high camber angle close to 4-5 degrees while for slow ones it is better to decrease it to increase the grip of the axis. Correct tire wear and the behavior of the car when cornering also depend on the camber angle.