Introduction
The camber is the angle formed between the vertical plane to the road surface and the plane passing through the center line of the wheel. Of course, there is a positive camber and a negative camber. If the top of the wheel leans towards the center of the car, this is called negative camber (-). If the top of the wheel leans towards the outside of the car, it’s called positive camber (+). If the wheel is perfectly vertical, the wheel has zero inclination and therefore neutral camber. Negative camber is the most common setting on a race car. The GIF below shows negative camber that increases and decreases.
The adjustment of the camber angle in motor sports
To have maximum road holding in every situation, it is necessary to ensure that the tires have and maintain the greatest possible contact surface with the asphalt. In static conditions, the ideal solution is naturally that of zero camber, i.e. with the wheel in a vertical position, perfectly resting on the ground (in the figure below the width of the contact surface is highlighted in yellow).
In dynamic conditions, guaranteeing the greatest possible contact surface with the asphalt is not easy due to the fact that the position of the tires with respect to the car is not constant but variable according to the dynamic effects of motion, i.e. the load transfers due to acceleration, braking, curves and disconnections of the terrain, in addition to the fact that the tires are deformed by the forces to which they are subjected. In fact, in the following figure we can see the effects of the lateral force that occur when cornering and which mainly consist in the transfer of load from the internal wheels to the external ones and in the roll, or the oscillation of the vehicle around its longitudinal axis, with the side the inside of the car that rises and the outside that lowers.
As we can see in detail in the following figure, together with the roll there is also a variation of the inclination of the tires with respect to the vertical.
The tire is now not perfectly resting on the asphalt and is bearing the load through a lower portion of the tread. The latter is also deformed by the lateral forces acting on the tire, further reducing the contact area and carrying part of the load towards the outer side. So, starting from a neutral camber, we now have the tire that tends to work with a much smaller contact surface (in yellow in the figure above) and particularly stressed. This will lead to excessive wear of the external part of the tread, temperatures that are difficult to manage (the overheated portion of the tire in red) and a consequent loss of grip and speed when cornering.
If, on the other hand, we set a certain negative camber angle, the external tire is now able to use the entire width of its tread much more easily when cornering, thanks also to its own deformation, with an increase in the contact surface which leads to better traction and grip.
So far we have focused attention on the behavior of the outer tire, as the previous images denote, and the reason is quickly explained. If we analyze the behavior of the inner tire during a curve, we will see that this is inclined in such a way as to rest with a large part of the tread and have an extremely small contact surface. But since cornering is the outer tire that bears most of the load (represented by the blue arrows in the figure below), concerns about the inner tire are minimal.
In fact, depending on the calibration and geometry of the suspension and the adjustment of its characteristic angles, the inner tire can be very close to the lift or even not infrequently it can completely detach from the track. So, very often, in such circumstances neglecting the inner gum can be the lesser evil.
However, the negative camber is not without its contraindications. In fact, like all adjustments related to car tuning, setting a certain camber angle has both advantages and disadvantages. The tire that has a non-zero camber when traveling a straight section wears excessively at the edges because the load on the road surface is not balanced.
In particular, in the case of negative camber, the internal shoulders are more loaded, which is detrimental to the durability of the tires as it increases the risk of punctures and wear caused by the increase in temperature, problems that we mentioned before.
Furthermore, during straight-line acceleration, maximum performance is obtained with zero degrees of camber at the rear; on the other hand, a certain angle of camber at the rear improves cornering grip. Observing the F1 single-seaters it can in fact be noted that the camber is rightly more accentuated at the front while at the rear it is still negative but with a lower value. This is because at the rear it is important to have as large a footprint as possible already at low speeds in order to maximize traction when exiting slow corners. It is therefore up to us to find the right compromise in adjusting the tire camber, also taking into account the following aspects:
- track layout
- geometry and stiffness of the suspension
- weight (amount of fuel in the tank)
- runway temperature
The experimental way to understand if our suspensions are adjusted with the right camber angle for the type of tires we are using is to make a few laps of the track and then re-enter and check the temperature values along the outer, central and the internal one of the 4 tires.
Remember: Camber gain is the change in camber angle due to vertical wheel displacement caused by suspension wobbling when the car is in motion. In the following image it can be seen that the lifting of the wheel has produced an increase in the negative camber; conversely, lowering the wheel would have the opposite effect on the camber. We speak of static camber when the camber is measured with the car stopped in the pits. When the car is in motion, the camber angle changes continuously due to the forces created by driving maneuvers such as accelerating, braking or turning; in this case we speak of dynamic camber. The dynamic camber angle is the total of the static camber angle plus the camber gain (to be added or subtracted).
When cornering, the extent of the change in the camber angle of the steered wheels is also influenced by the caster angle. More precisely, the outer wheel will tend towards a more negative camber, while the inner wheel will tend towards a positive camber. This occurs in a proportional manner, that is, the greater the caster angle, the greater the effect of the variation of the camber in the curve; also in this circumstance we speak of dynamic camber.
Camber adjustment on Assetto Corsa Competizione
In GT3 and GT4 cars, on which Assetto Corsa Competizione is focused, it is preferable to use a high negative camber, both front and rear, as this will increase the contact area of the tire in high load corners. It should be noted that negative camber can cause an uneven rise in temperature in the three sections of the tire: outer (O), center (M) and inner (I).
When adjusting the camber be sure to keep the outside-to-inside temperature variation below 9° C for the front tires and 5° C for the rear tires.
Below are the changes to be made to the camber angle to solve the main handling and performance problems of the car and tire wear.
Oversteer
- corner entry: increase the negative camber at the rear;
- cornering: increase the negative camber at the rear;
- corner exit: increase the negative camber at the rear.
Understeer
- corner entry: increase the negative camber at the front;
- cornering: increase the negative camber at the front;
- corner exit: no benefit from camber angle adjustments.
Poor straight line top speed
- increase the negative camber (on straights a very cambered wheel creates less friction than a 0° camber wheel).
Poor acceleration and/or skidding at low speeds
- reduce the negative camber on the drive wheels, approaching zero.
Overheating and/or excessive degradation of the outer edge of the tires
- increase negative camber.
Overheating and/or excessive degradation of the inner edge of the tires
- reduce negative camber.
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