Semi-trailing Arm Axle
The semi-trailing arm suspension should precisely guide the rear wheels, independently of each other with cast, forged or from steel-plate manufactured elements. The steering axles of these elements are neither parallel to the longitudinal- nor to the transverse axis of the vehicle.
The rear wheels are guided by wide arms. These are attached to the springs (mostly coil-springs) and the shock absorbers. The rear view (picture above) and the top view (picture below) of the swivel-axle arms show their slanted position. The one seen from the top is more distinct and provides for negative camber when the springs are compressed or when they rebound. The slanting position seen from the rear emphasises this effect when compressing, and weakens it in equal measure when rebounding. Because the final drive is bolted to the vehicle floor, to reduce the unsprung mass, as in all independent suspensions, universal joints to the wheels are necessary. Trailing arms are found with driven rear axles.
The wide construction requires a great deal of space. However, because in modern rear-wheel drive vehicles, the fuel tank is mounted in front of the rear axle, (under the rear seats) a lot of space is no longer available. Apart from that, the resonant steering behaviour of the rear axle when the springs are compressed, is only slightly changeable. This is why the relevance of the semi-trailing arm axle is decreasing more and more.