Double wishbone

A double wishbone (also called a double A-arm) suspension holds the wheel upright between two triangular arms. Each wishbone pivots on the chassis at its wide end and connects to the upright, or knuckle, through a ball joint at its narrow end. The coil spring and damper usually sit on the lower arm as a coil-over unit and are separate from the job of locating the wheel. You will find it at the front of body-on-frame SUVs and pickups such as the Toyota Fortuner, Mahindra Scorpio-N and Mahindra Thar, and in some premium sedans.

• Over a bump the wheel rises and both arms swing upward about their chassis pivots.
• Because the upper arm is shorter than the lower one, the top of the wheel tilts inward slightly as it rises. Engineers choose the arm lengths so the tyre stays flat on the road while the body leans in a corner.
• The coil-over compresses; the damper turns the movement into heat so the body does not keep bouncing.
• Steering turns the upright on its two ball joints while the arms stay put.

The arms take all the cornering, braking and bump loads, so the spring and damper only have to do their own jobs; this is why the layout is used in racing. The driver feels planted, consistent cornering and good steering feedback, and off-road the design copes well with long wheel travel. The price is more parts, more ball joints and bushes to wear, and more space taken up on either side of the engine.