Torsion beam axle

The torsion beam, also called a twist beam or coupled torsion beam axle, is the rear suspension of almost every front-wheel-drive hatchback, sedan and compact SUV sold in India, from the Maruti Swift and Baleno to the Hyundai Creta and Tata Nexon. Two trailing arms, one on each side, pivot on rubber bushes under the body and carry the rear wheel hubs at their back ends. A beam with a U- or V-shaped cross-section welds the two arms together, and a coil spring and damper sit between each arm and the body.

• When both wheels rise together, for example over a speed breaker, the whole assembly simply swings up about the two front bushes and the springs compress.
• When only one wheel rises, that arm swings up alone and the crossbeam has to twist along its length; its open section is designed to be stiff in bending but soft in torsion.
• The twisting beam acts as a built-in anti-roll bar, pressing the other wheel down so the car leans less in corners.
• The springs and dampers return each wheel to the road at a controlled speed.

Because the wheels are coupled through the beam, the layout is called semi-independent. The driver notices a slightly busier ride on broken roads than a multi-link car, and the inside rear wheel can lift on hard cornering, but for everyday driving the difference is small. The advantages are a flat floor, a deep boot, few moving parts and low cost, which is exactly what a budget car needs.