Running gear

When suspension is defined as the totality of all parts of a vehicle, serve to connect the car body (chassis or unibody ) via the wheels to the road.

Road vehicles

PTO and structure, the chassis is one of the main components of the automobile and consists of wheels, wheel carriers, wheel bearings, brakes, suspension, subframe, suspension with stabilizer, damping, steering.

For cars with unibody construction, the chassis is not part of the chassis, but is considered as an independent module.


The "wheel", actually the wheel and tire combination consists of tires and a rim. The wheel represents the entire body, consisting of rim and disc ( wheel disc ) or wheel spider or spokes with hub part. The rim serves to receive the tire. Wheel disc, wheel spider or spokes with hub part used for central mounting of the wheel to the wheel hub. " Complete " is the term for the complete wheel (tire, wheel and valve). In practice, the terms and wheel rim are often confused.

The " wheels " are the point of contact between the undercarriage and road. This gives you significant impact on the dynamics. They belong to the unsprung mass of the vehicle and therefore should be as light as possible. By the changing loads high demands are made in terms of the strength of the wheels and of the wear of the tires. The tires must make possible a slip-free connection to the road in any weather and different road surfaces. The secure contact of the wheels with the road ensures the suspension.


When suspension is any components for movable connection between the wheels and the chassis or monocoque body. Transfer steering, braking and acceleration forces all. The suspension is mounted in a vehicle with frame construction directly to the frame. On vehicles with self-supporting body called subframe are often used around the parts of the suspension to the body join.


By steering device can be a non- rail-bound vehicle in a desired direction control. The wheels turn at each steering angle a defined by the suspension geometry position one another. The steering trapeze allows different turning angle ( toe angle ) of the front wheels, the inside wheel is more taken as the outer curve.


The chassis has to transmit delay forces as little slip on the road. Providing deceleration forces assumes the wheel brake and the operating brake. Service brakes are all components of a brake that are under the direct influence of the driver to reduce the speed, for safe stopping and holding the speed. They are mounted on the chassis and act directly on the wheels. However, special designs can also act via a drive shaft to the wheels.

Suspension settings

The driving dynamics of the suspension depends on the suspension geometry, mass distribution and the force characteristics. The following, partly modifiable parameters are relevant:

  • Camber: Camber is the tilt of a wheel, ie the deviation from the vertical position. The deviation is called camber angle. Is the wheel tilted outward ( as if it would fall to the outside ), is the overthrow of " positive", it is inclined inwards, is the overthrow of "negative".
  • Track: The track angle is the angle between the longitudinal axis of the vehicle projected onto the road and the intersection between wheel center and the road plane.
  • Toe: The toe angle is straight when the steering wheel angle position of the toe angle. Previously, the toe was given in mm. The distances of the inner rim edges of the wheels on one axle, were, front and rear measured at the height of the wheel center and subtracting the two values ​​. Is the distance to the wheel front than at the Radhinterseite, the toe-in is positive. But if he is behind smaller than the front toe-in is negative. In this case one speaks of the so-called toe-out. At the rear toe is used to improve the driving stability. Disadvantage of too much toe-in may be the tire wear.
  • Wheelbase: The wheelbase is the distance between two axes in the longitudinal direction of the vehicle, measured in the center of the wheel. For vehicles with more than two axles several wheelbases be specified.
  • Lag ( lag distance ): See follow-up.
  • Steering roll radius / steering roll radius: The scrub radius is the vertical distance between the intersection point of the expansion axis ( steering axis ) by the road and the intersection between wheel center and the road plane. If the intersection point further out than the wheel contact point, the value is negative.
  • Travel: The way a wheel is, travels between the inset and inset position out of travel. It is measured perpendicular to the road. The travel between the static deflection under the vehicle is empty and at full deflection is referred to as ' positive travel ', the travel between the static deflection with an empty vehicle and the fully compressed state ( raised vehicle) is referred to as ' negative spring travel '.
  • Spring characteristics: The characteristics of a spring is shown in a diagram in relation to the spring travel of the spring force. The slope of the line shown is the spring constant.
  • Natural frequency: The natural frequency is derived from the relationship between the spring constant and the mass of a resilient system. She is shown in a diagram and should be as constant as possible. This is achieved with a progressive spring characteristic.
  • Damping capacity: In force-displacement diagrams and force-velocity diagrams, the force is displayed to the deceleration of the motor (the way of the shock absorber piston ) as a damping force. More progressive, the curves indicated the greater the attenuation capacity of a system.
  • Instantaneous ( instantaneous center ) and roll center: The instantaneous center is simplified with a double wishbone suspension, the intersection considered both handlebar center lines of a side of the axle. Are drawn from the moment Poland both sides line through the wheel contact points, we obtain the instantaneous center. Both change their position in spring movements of the chassis. Both of which are critical for the driving stability, and must be taken into account in the design.
  • Roll axis: The roll axis is the line connecting the roll center of the front and rear axle. When attacking from side forces such as centrifugal or inertial forces at the centroid of the vehicle body staggers around this axis.
  • The thrust angle is the angular difference to the outside wheel against the inside wheel is less cramped by ..

Related Topics

The track model is a simplified model of the lateral dynamics of two-lane vehicles with pneumatic tires.


For aircraft, the landing gear is used for rolling (English: taxi ), takeoff and landing as well as for moving the aircraft on the ground ( eg helicopters). In the latter case, the aircraft may not necessarily be driven by its own engines, but can also be towed or pushed backward to ( pushback ).

In most larger aircraft, the landing gear at the start after lifting retracted ( retractable ) to reduce air resistance. It is extended again until before landing.

Track vehicle

In rail vehicles, the chassis is referred to as a drive. It takes over the secure and convenient management of the vehicle on the track and transmits the forces.

Literature and sources

  • Automotive chassis 5th revised edition 1987
  • " Automotive technology " of Holland Jose Hans -Verlag Stuttgart
  • " Automotive engineering " of EUROPE - FACHBUCH SERIES - European Publishing teaching aids