Rear Semi-Trailing Arm

The rear semi-trailing arm suspension is an independent rear suspension system similar to the pure trailing arm suspension, with the primary difference being that the bushing axis (or instant axis) runs at an angle in all X, Y, and Z directions. The rear semi-trailing arm suspension combines the advantages of the trailing arm and double-pivot swing axle suspension principles, without the associated disadvantages. The semi-trailing arms resemble triangulated wishbones, with the pivots arranged at an angle to the vehicle's transverse axis and either horizontal or slightly towards the vehicle's centerline.

Figure 1. Rear Semi-Trailing Arm Suspension

Model Use

The rear semi-trailing arm suspension system can be used in either a half car or a full vehicle analysis. The default geometry and mass is that of a passenger car or light truck, however the model and data can be revised to reflect any size vehicle, from a large truck to a scale model car.
  • The wheel body represents the mass and inertia of the tire and the rim.
  • The wheel hub body represents the mass and inertia of other rotating bodies such as a brake rotor, but not the half-shafts if the suspension is driven. The wheel hub and brake rotor have no associated graphics.
  • The wheel and wheel hub parts use the Wheel CG location as the center of gravity.
  • Each body’s Center of Gravity (CG) is estimated from the body’s geometry. The formulas are coded into the point panel and can be seen via the graphical user interface. If more accurate CG locations are available they should be used.
  • A wide variety of combinations of suspensions and subsystems can be built using the Assembly Wizard. You are encouraged to build systems and understand the resulting model using the graphical user interface.

    When building a new suspension model, build the model with all of the optional systems (stabilizer bar, etc) included in the model. Immediately turn off the systems using the Project Browser and run an analysis on the base suspension to ensure it solves properly. As data becomes available for the optional systems; activate those systems and populate them with data.

The image below shows the Project Browser view of the systems in a fully populated rear suspension model. The Rear semitrail arm susp system has five “child” systems.

Figure 3. Browser View of a Rear-Half-Vehicle Model Systems and Subsystems Employing a Semi-Trailing Arm Suspension


Attachments determine how the suspension system connects to the rest of the vehicle. The rear semi-trailing arm includes attachments for the trailing arm, the upper link, and the lower link:
Entity Attaches To
Trailing arm, upper link, lower link Default: Sub-frame

No subframe: Vehicle body

No vehicle body: Ground

You can also set any attachments using the Attachment Wizard, or by selecting the subsystem in the Project Browser and revising the attachments on the System/Assembly panel.


Points locate the joints and bushings that connect the suspension bodies to one another. The image below shows the principal points for the rear semi-trailing arm suspension:

Figure 4. Right Side Principal Points – Rear Semi-Trailing Arm Suspension
Note: The image above omits the left side of the suspension, points locating body centers of mass, and points that locate the optional subsystems (springs, dampers, bump stops and stabilizer bar) for clarity.


The rear semi-trailing arm suspension is comprised of the bodies shown in the image below:

Figure 5. Right Side Bodies – Rear Quad-link Suspension

Bushings and Joints

The table below describes the bodies, bushings, and joints for the rear semi-trailing arm suspension:
Note: The table omits the left side joints for clarity.
Label Type Body 1 Body 2 Point
Trailing Arm Wheel Revolute Joint Revolute Wheel Hub Semi-Trailing Arm Wheel Center
Wheel Hub

Fix Jt

Fixed Wheel Wheel Hub Wheel Center
Inner Toe Link Bush Universal Toe Link Semi-Trailing Arm Inner Toe Link
Outer Toe Link Bush Ball Toe Link Semi-Trailing Arm Outer Toe Link
Trailing Arm Outer Bush Bush Semi-Trailing Arm Vehicle Body Outer Trail Arm Bushing
Trailing Arm Inner Bush Bush Semi-Trailing Arm Vehicle Body Inner Trail Arm Bushing
The following image shows the location of the joints and bushings in the suspension:

Figure 6. Right Side Joints and Bushings: Rear Semi-Trailing Arm Suspension