Spindles are a component of the suspension system in a vehicle that enables it to drive forward, backward, turn in both directions and brake. Although suspension systems may differ for each make of vehicle, the role of the spindle remains the same.
Also known as “steering knuckles,” the basic function of a spindle is to allow an axle (a shaft that supports the wheel bearings) to rotate. The axle, in turn, is connected to the vehicle’s suspension system and wheels. Spindles hold the hub of the wheel in place and connect to the arms of each wheel via the axle on the suspension system.
The spindle also functions by gearing the vehicle in a straight line in what is called a castor. The caster is the negative (forward) and positive (backward) tilt that adjusts the steering process, thanks to a spindle that is connected to the steering axis.
Spindles can function on many different types of suspension systems. In the MacPherson Strut, commonly used in European vehicles, the spindle is connected to an arm in the front and back of the suspension frame. The spindle functions on this type by allowing the shock absorber housing to turn the wheel.
Another common type is the Double Wishbone or Double A Wishbone, where the spindle is connected to a lower and upper A-shaped rod arm. Multi-link suspensions are another commonly used suspension type that utilizes the spindle function. It is similar to the Double Wishbone with two A-shaped arms, but they are separate from each other.
In rear wheel-drive cars, the axle is part of the spindle; as opposed to front-wheel drive, where the spindles are fitted with bearing pockets.