What is MacPherson strut? Not always what you think

The column is an invention of Earl McPherson and the most popular suspension design that has been used for decades until today. However, it is often confused with a pillar, which can make a difference when you decide to buy a car. I already explain why.

The idea of ​​the MacPherson strut is to combine simplicity and efficiency. Therefore, it is an extremely popular solution in almost every vehicle segment. The structure consists of three elements that must be applied to be called a MacPherson strut:

• Shock absorber with spring strut
• Lower wishbone
• Steering

And nothing more. The system rests in the upper part on the shock absorber cup, which is part of the body in which the rack is mounted on a rotating bearing. This rack, or rather the shock absorber, is attached to the bottom of the steering knuckle in its upper part. The rotary fist from below rests against the rocker. The rocker arm is usually a so-called triangular, which means three attachment points - two bushings (front and rear) attaching to the body and a steering knuckle trunnion that connects to the steering knuckle. The exception is one-arm struts (two attachment points) through which the anti-roll bar passes. The whole, that is, the three elements mentioned, constitute MacPherson column.

The column performs three functions:

• leading, 
• jumped up
• twisting.

It is worth emphasizing here that MacPherson struts are used only on the front axle.

A suspension is MacPherson strut if it meets the following conditions:

• this is the front suspension
• the shock absorber and spring form an integral part known as the strut,
• shock absorber and steering knuckle after installation in the car form a single element,
• one control lever attached to the bottom of the steering knuckle is responsible for steering,
• the spring strut rotates about its longitudinal axis when we turn the front wheels.

It is mistakenly called MacPherson strut, more precisely MacPherson strut, the most resistant, that is, the shock absorber and spring assembly. Such solutions are used in double or multi-link suspension, both front and rear. However, this is not a MacPherson strut, which always has only one lower arm. It's also not a HiPerStrut or RevoKnuckle axle, which look exactly the same, but the shock is separate from the crossover so it doesn't rotate with the crossover.

Benefits of MacPherson struts

In addition to its simple and compact, lightweight, low-maintenance design, the MacPherson strut also has kinematic advantages. First of all, this provides a large wheel travel and high resistance to changing conditions (roughness and their combination with spin). The design is advantageous in terms of stability and maneuverability. The column also provides sufficient stability when braking.

The advantages, however, mainly relate to low-power vehicles (front-wheel drive) and rear-wheel drive or 4x4 vehicles. When more power needs to be transferred to the front axle, the classic MacPherson strut shows its disadvantages, as it performs three functions at the same time.

Disadvantages of MacPherson struts

The most important thing is to change the geometry, and specifically the position of the wheel relative to the ground when turning. Thanks to the two attachment points, this is a relatively delicate solution, not rigid. This is why MacPherson struts are relatively rarely used in vehicles with high power to the front axle and in heavy vehicles. The other issue is that you need to use long offset wheels when you want to put wide tires on the rims. This, in turn, increases the unsprung weight.

MacPherson strut in use

This is actually the biggest advantage of this solution. It does not require maintenance, but thanks to only three elements it is very cheap to repair. The lower transverse arm wears out most often, and this one is very often a regenerated element. We are talking about the possibility of replacing the steering pin and rubber bushings (the so-called silent blocks). Other, very cheap components are the stabilizer links. It will be more expensive only when using an aluminum pendulum with a non-replaceable pin in the column. However, even such a lever is usually cheaper than a set of levers in non-MacPherson solutions.

The problem with MacPherson struts is the strut, that is, the integrated damper with a spring. The shock absorber must be removed to replace the spring. On the other hand, the entire rack has another damping element in the form of an upper rubber cushion with a bearing. It is also replaced with almost every shock absorber replacement.