semi-trailing
Having a movement that pivots on an access which is at an angle between longitudinal and transverse.
semi-trailing: suspension pivot halfway between front and side
A semi-trailing arm is a suspension link that pivots on an axis angled between the car's longitudinal (front-to-back) and transverse (side-to-side) directions. The pivot point sits somewhere between 45 and 60 degrees from the centerline in most applications. This geometry creates a compromise between the behavior of a fully trailing arm, which runs purely lengthwise, and a semi-leading arm, which angles forward.
The angle of the pivot axis determines how the wheel moves under load. When the suspension compresses, the wheel tracks inward and upward simultaneously, a motion called camber change. The degree of inward movement, called anti-squat or anti-dive, depends entirely on how steeply the arm's pivot axis is angled. A shallower angle produces less anti-squat; a steeper one produces more. Designers tune this angle to control how the chassis pitches during braking and acceleration.
Semi-trailing arms became standard on the rear axles of front-wheel-drive cars from the 1970s onward, particularly in European designs. They appear on vehicles ranging from compact hatchbacks to high-performance sports cars. The geometry is less common on rear-wheel-drive or four-wheel-drive vehicles, where different suspension types dominate. Some manufacturers have used them at the front as well, though this is rarer.
The appeal is straightforward: semi-trailing arms use simple materials and fabrication. The arm itself is usually a stamped or welded steel forging that bolts to the chassis at one end and to a wheel hub carrier at the other. The pivot bushings are rubber or elastomer, making the system cost-effective to produce while still offering good compliance and isolation from road noise.
The main drawback is handling behavior under extreme lateral load. Because the wheel's camber angle changes as the arm moves, bumps and hard cornering can cause unpredictable shifts in tire contact patch. Many modern designs have replaced semi-trailing arms with multi-link or double-wishbone systems to reduce this effect, but the semi-trailing arm remains common in volume production vehicles where cost and simplicity outweigh the performance penalty.