In fact, there are several parameters to the geometry of the suspension. Most of them concern the steering axle, some, however, also apply to the non-steered axle, the geometry of which also significantly influences the behavior of the car on the road. There are also parameters for the geometry of the chassis as a whole. Only some of them may be regulated. In modern high-volume production vehicles, designers resign from most possible adjustments. It doesn't, that non-adjustable parameters cannot be measured. On the contrary, measurements are necessary, to determine any possible use of-
acts of poor car behavior on the road and stated, which suspension components are damaged, and even whether the fault is not on the side of the skewed body (framework).
• First, let's mention the most famous toe-in of the front wheels (guided). This is the difference in distance between the edges of the rim, set symmetrically to the car's longitudinal axis, measured at the wheel axis. This value is adjustable in every car. The main goal is to align the wheels relatively parallel to the longitudinal axis of the car in various road conditions. Due to the susceptibility of the suspension mounting points (rocker arms, reaction bars) convergence measured statically, when the vehicle is stationary, There are values that differ significantly from one car model to another. Typically, for rear wheel drive vehicles, the toe is positive, while for the front wheel drive it is close to zero or negative (discrepancy), although this is not necessarily the case.
It must be noted, that the toe-in of the steered wheels has a significant effect on the service life of the tires, resistance to motion and in case of significant (that is already a few millimeters) differences from the recommended values, for stability when driving straight ahead. The convergence, however, has nothing to do with the so-called. "Downloading", because it concerns a pair of wheels, not one side of the car. The toe-in tests should be performed after replacing any component of the front suspension. When adjusting other parameters of the suspension geometry, the toe-in measurement and adjustment is always done last and usually under a certain load. Adequate adjustment of the length of the steering rods should be brought about, so that the steering gear is always in the center position when driving straight ahead.
The problem may be the damage to the metal-rubber mounting points of the rocker arms or stiffness that is difficult to statistically assess (np. cracked) lengthwise. In this case, the toe-in while driving may differ significantly from the toe-in measured on the test bench.
• Equally important is the toe-in of the rear axle wheels. It is rarely and only regulated then, when we are dealing with a fully independent suspension. There is no easy way to change this parameter on the rigid axle and semi-dependent suspension, so if it is different from the nominal, means, that the axis is damaged. Let us pay attention, that if the rear axle is not steered, wheel alignment is assessed separately for the right and left sides of the car. When it is not the same, the vehicle moves "sideways", which in critical conditions may cause loss of stability. Usually, the toe-in of the rear axle is definitely positive, which helps to maintain traffic stability during sudden changes of direction.
• Another parameter of the steering system is the difference in the turning of the left and right wheels. It depends on the design of the steering system and the geometrical dimensions of its elements, so it cannot be regulated. The mutual steering angles of the wheels can, however, be measured and on this basis the condition of the steering system and the frame can be assessed, also after the accident. When the values are incorrect, the car can wear out tires excessively and lose grip in bends.
• Camber is the angle between the plane of the wheel in the straight ahead position, and a plane perpendicular to the ground and parallel to the longitudinal axis of the car. In older service manuals it is stated, that the angle should be positive (the wheels spread apart) due to the improvement of the durability of the bearings and the reduction of the force needed to turn the steering wheel. With today's bearing design, the first factor is irrelevant, and against the fact, that most cars have power steering, the second is also losing importance. In modern vehicles, camber is either zero or negative, which increases the contact area of the tire with the ground at high speed in a turn. The choice of this angle depends on the construction of the suspension and the character of the car – in sports it is usually negative. The camber of the wheel applies to both the front and rear wheels. This parameter can be adjusted in some popular cars, although producers are slowly moving away from this possibility, based on the precise manufacture of the suspension points and their fastening.