The inclination of the axis of the kingpin (applies to the steering axle) it is the angle between the straight line passed through the switch pin (np. by two wishbone joints or by the upper McPherson strut mount and a wishbone joint), a perpendicular to the ground. In production cars it is practically not subject to regulation, is regulated together with the camber angle. An important design parameter of the suspension is the interdependence of these two angles. If the axle of the steering knuckle pierces the ground on the "inside" side of the median plane of the wheel (A), there is a positive swing radius (when turning the wheels). Contrary, when it penetrates the ground plane on the "outer" side from the median plane of the wheel (B), this swing radius is negative. The latter solution is used in many modern cars, mainly front-wheel drive. It significantly reduces the steering forces from the variable traction of both wheels during acceleration and braking. Especially it allows you to keep a straight track during braking, when the cross-split brake system is partially defective.
• Wyprzedzenie osi sworznia zwrotnicy jest to kąt pomiędzy prostą przechodzącą przez sworzeń zwrotnicy a prostopadłą do podłoża, measured in a plane parallel to the car axis. This angle may be adjusted in some designs, although this happens less and less. The existence of this angle, different from zero, causes, that the front axle wheels automatically return to straight-ahead after being turned. This phenomenon occurs with the correct combination of the lead angle and the tilt of the kingpin axis. In practice, both of these angles can only change with serious damage to the suspension or the bodywork (framework). Change these parameters, especially this one, that the angles mentioned will be unequal on the right and left sides of the car, will cause, that the car will be – automatically turn when driving straight ahead ("download"). Unfortunately, same as when adjusting toe-in, in a worn-out car (non-rigid suspension mounting elements) these parameters may clearly differ between measurements on the bench and while driving (np. after braking), which makes it extremely difficult to obtain the proper effect – good driving.
• Biorąc pod uwagę obie osie pojazdu, we get some specific parameters: angle between both axes, steering angle of the rear axle, offset angle of both axes, rear axle yaw angle, difference between left and right wheel distances, finally, the yaw angle of the line joining the two wheels of one side of the vehicle. Except for very special suspension designs, the axles of the vehicle should be parallel to each other and symmetrically with respect to the car's axis of symmetry. Most cars have different track widths for the front and rear axles. None of these parameters are regulated. Therefore, if during the measurements we find a deviation from the nominal parameters, it is the result of damage to the suspension components or the frame. Such a car can drive poorly and, what is worse, it can be difficult to detect in good road conditions.
However, it is very dangerous with low and variable wheel traction.
• Bardzo rzadko kontrolowanym i niedocenianym parametrem jest siła nacisku poszczególnych kół na (perfectly horizontal) subsoil. Checking, using the correct weight, These values give an overview of both the condition of the spring elements and the possible deformation of the frame (bodywork) as a whole. Excessive differences in wheel pressure on one axle significantly affect the deterioration of the car's driving. In mass-produced cars, the position of the supports of the suspension elements is not regulated, they can only be changed by replacing the relevant parts.
There is actually no reason, in the normal operation of the car any of the above-mentioned parameters, determining the geometry of the suspension was automatically changed significantly. However, in the event of an accident, even when the overloads in the car leaving the road were small and the body was not damaged, the elements and suspension mounting points may be deformed. It is therefore necessary to check the geometry of the chassis on an appropriate test bench. In practice, even a single sudden hitting a curb or a hole in the road may result in damage, which will worsen the car's handling and accelerate tire wear.
Can any of the above-mentioned values be tested under amateur conditions?? Theoretically yes, but this only applies to toe-in and camber angles. A stubborn tinkerer can check these parameters, having a hard level surface, string, with a weight and a caliper. Nay, such a measurement (the measurement method is omitted here) it does not have to differ in accuracy from the results obtained on a computerized diagnostic stand, as long as we assume, that the ground is really level, the rims are not distorted, correct load on the car, etc.. In practice, there are too many doubts and self-measurements of the suspension geometry are not recommended, especially, that the determination of the remaining parameters already requires special measuring instruments.
Another thing is the diagnosis of the suspension while driving, that is, an attempt to state, whether a visit to a diagnostic workshop is necessary. Any change in the car's behavior on the road should raise our concern, and in particular the spontaneous shift of the steering wheel when driving straight ahead. A disturbing symptom will also be a change in the direction of travel ("download") when driving straight ahead, when braking, accelerating or coasting. By detecting such phenomena, we should immediately check the condition of the tires and tire pressure, and if we do not find the reason for the change in the behavior of the car, go quickly to a diagnostic workshop.