In this brief article, we will discuss the trailing arm, the control arm and the differences between the two. We will also discuss the different types of trailing arm Suspension
What is the difference between a Trailing arm and a Control arm?
Control arms are used to constrain the axle or wheel knuckle in a particular degree of freedom (DOF). A Trailing arm is a type of control arm. The speciality of a trailing arm is that it is mostly used to constrain the longitudinal or fore-aft DOF. In the side view and top view, the trailing arm will appear to connect the chassis to the bottom of the axle or wheel knuckle in the backward longitudinal direction. Control arms usually tend to connect the chassis to the wheel in the lateral direction or even at an acute angle to the lateral direction, when viewed from the top.
However, control arms that are longitudinal and connect the chassis to the top of the axle are generally called Upper control arms, even though they are longitudinal.
What are the different types of Control Arms?
The different types of Control arms are:
- A-Arm or Wishbone: The same control arm attaches to 2 points on the chassis
- Trailing arm, longitudinal arms: The forward attachment point is to the chassis and the rearward point is to the axle/wheel hub
- Lateral control arms: The control arm is parallel to or at a slight angle to the vehicle’s lateral axis
- Toe-Control arm: The control arm is parallel to the vehicle’s lateral axis but connects to the front of the wheel when viewing from the top
What is a Trailing Arm Suspension?
Trailing arm suspension is defined as the type of suspension where the axle or wheel “trails behind”. The typical geometry of a trailing arm is a longitudinal link (either parallel to the car’s longitudinal axis or at an angle) that has its forward end pivot attached to the chassis and the trailing end attached to the axle or wheel.
What are the different Types of Trailing Arm Suspension?
The Different Types of trailing Arm Suspension are:
- Rear wheel drive/ Live axle Trailing Arm
- Torsion Beam trailing arm Axle
- Semi-Trailing Arm
- Semi-trailing arm Multi-Link
Different Types of Trailing Arm Suspension?
Rear Wheel Drive Trailing Arm
This type of trailing arm is seen on vehicles with a
Rear wheel drive vehicles with a live axle. The rear wheel drive type of trailing-arm suspension has longitudinally oriented suspension arms that are pivoted perpendicular to the longitudinal axis of the vehicle.
The trailing arm takes up acceleration and braking loads, resists lateral forces and resists roll as well.
The disadvantage with this type of dual-link Trailing arm, the two perpendicular bushings allow almost no freedom to twist.
Torsion Beam trailing arm Axle
The rear Torsion-Beam axle is a very popular and cost-effective rear suspension setup, mostly used on cars with front wheel drive. The trailing arms are joined laterally midway using a torsion beam. Because of the geometry, when there is a roll motion, the torsion beam twists. The torsion beam basically plays the role of an anti roll bar and resists rear suspension roll motion.
The axle is hinged onto the chassis using only two bushings (one at each rear corner) oriented perpendicular to the vehicle center-line.
Notable examples are the Front wheel drive cars of the Audi A1 Sportback, based on the “MQB” platform, on which the Polo Mk6 and SEAT Ibiza Mk5.
A Semi-trailing arm is almost the same as a Trailing Arm suspension, with the only difference being the bushing axis is at an angle to the vehicle center-line. The bush axis angle to the center-line varies between 45 to 70 degrees.
The major advantage in the semi-trailing arm is its ability to allow roll motion by relieving twist, which was the disadvantage with the Trailing arm. The other advantage is that when the rear suspension rolls, there is minimal effective steer to the rear wheels. The result is more stable handling characteristics with almost neutral steer.
A Notable example from the past is the BMW E30 rear suspension.
Semi-Trailing Arm Multi-link
Another variation in the Semi-Trailing arm Suspension is the Trailing Arm Multi-link (4-Link) independent rear suspension found in the rear suspension of many modern cars.
In the trailing arm multi-link, the trailing arm is hinged by a bushings at the chassis end bolted to the wheel knuckle at the other end. In order to constrain other degrees of freedom, there would be an upper control arm and a lower control arm connected to the upper and lower ends of the knuckle, and a toe-control arm. A Notable example is the Audi A3 rear 3-link suspension.
In this brief article, we have discussed the trailing arm, the control arm and the differences between the two. We have also discussed the different types of trailing arm Suspension.