 Kingpin Inclination Angle Theory
The kingpin inclination is the angle, measured in degrees, that forms the line passing through the kingpin and the perpendicular to the ground, looking at the vehicle from the front,
Wheel camber angle was devised to reduce the kingpin offset, which is the distance between the projection to the ground level of the kingpin axis and the point of contact with the tyre,
But it was noted that a marked increase in this angle created negative effects, especially with the tyres at low pressure, the specific need arose, to reduce the camber angle almost to zero, this was also to achieve regular wear on the tyre, the problem was resolved by inclining the kingpin towards the lower part of the wheel,
With rigid-axle suspension systems, the inclination of the kingpin does not vary under the effect of load and the vertical jolting of the vehicle, providing there is no axis deformation, in independent suspension systems, however, the load and vertical jolting of the vehicle cause both the wheel camber and the kingpin inclination to vary to the same degree, as the kingpin forms a single block with the wheel hub,
Included angle
The angle between the kingpin axis and the wheel axis is equal to the algebraic sum of the kingpin inclination angle and the wheel camber angle and is defined as the included angle,
Example
| |
1st case |
2nd case |
| Wheel camber angle |
+2 deg |
-1 deg |
| +
Kingpin inclination angle |
6 deg |
8 deg |
| = included angle |
8 deg |
7 deg |
The included angle can vary only if there is a deformation between the kingpin axis and the wheel hub axis, if, during the checking operation, it is noted that the kingpin inclination angle and the wheel camber angle differs considerably from specified values, then before deciding what action to take it is advised to check to see whether the included angle has remained unchanged,
Example
| |
Specified Values |
Observed Values |
| Wheel camber |
+2 deg |
+1 deg (less than spec,) |
| Kingpin inclination |
6 deg |
7 deg (more than spec,) |
| Included angle |
( +2 deg 6 deg ) = 8 deg |
8 deg = constant |
In this case, the likely deformation, or irregular positioning of the parts, will be related to either the suspension arms or the suspension arm mounts, in this case the kingpin and the wheel hub positioning has not changed,
If, on the other hand, the following measurements are observed,
Wheel camber +1 deg
Kingpin inclination 6 deg
Included angle 7 deg = inconstant
Then there is a deformation in the kingpin-hub assembly,
The kingpin inclination angle, amongst other thing, creates the phenomena of the return of the wheels to straight position after a steering operation, it also tends to maintain this position after an impact with an obstacle that attempts to alter the trajectory,
This natural effect, which is vitally important, due to the inclination of the kingpin, derives from the fact that the wheel, when turning about this oblique axis, forms an inverted cone,
The hub is at it’s highest point relative to the ground, when the wheels are in the straight ahead position, when steering to the left or right, the hub lowers down nearer to the ground, consequently the wheels would tend to go beneath ground level, as they are unable to do this, this causes the body to rise up into an unstable position, thus, when turning the steering wheel, the driver not only generates the turning of the wheels but also, because of the weight of the vehicle, causes the raising up of the body, as soon as the driver ceases with the steering action, the body, due to the natural tendency by its own weight, goes to it’s lowest point, with this movement, causing a turning action which takes the wheels back to the straight line position, obviously, the heavier the vehicle or the bigger the kingpin inclination, the greater will be both the force exerted by the driver in the steering action and the speed with which the steering goes back to the mid position,
The evident result of this is that the weight of the vehicle tends to take the wheels to the straight line position, therefore, each perturbation force on the straight line direction of the -
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