MacPherson strut

The MacPherson strut is the front suspension on almost every hatchback, sedan and compact SUV sold in India, from the Maruti Swift and Hyundai Creta to the Tata Nexon. It packs the coil spring and the hydraulic damper into one upright unit, the strut, which bolts to the steering knuckle at the bottom and to the car body at the top through a rubber mount with a bearing. A single lower control arm (wishbone) locates the bottom of the knuckle to the subframe, and a tie rod from the steering rack turns the whole assembly.

• The tyre meets a bump and the wheel and knuckle move upward.
• The strut, which is fixed to the knuckle, telescopes: the damper rod pushes into the damper tube and the coil spring compresses.
• Oil inside the damper is forced through small valves, converting the bounce energy into heat so the car settles instead of bouncing.
• The lower arm swings on its bushes to guide the wheel up and down; the top mount bearing lets the strut rotate when you steer.
• The spring pushes the wheel back onto the road while the damper controls the speed of the return.

Because the strut replaces an upper arm, there is nothing above the wheel but the strut tower, which frees space in the engine bay of a front-wheel-drive car. The driver notices a soft, forgiving ride and light steering; on hard cornering a strut car tilts its outside tyre a little, which is why performance cars prefer double wishbones. Worn struts show up as a floaty ride, knocking from the top mounts, or uneven tyre wear.