In recent years, we have grown accustomed to Formula 1 cars adopting a generalised suspension layout, featuring a push-rod system at the front and a pull-rod system at the rear, with few exceptions.
The main reason for that approach was to package the suspension's mechanical elements (the rockers, the dampers and torsion bars), but the two systems also vary in stiffness and react differently to the downforce load produced while the car is running.
The two systems differ in how they operate due to the variations in their lever class.
A push-rod system is a first-class lever, which means the fulcrum (the point against which a lever is placed to get purchase) sits between the power force and the resistance point. To press with a relatively small amount of force, you need the distance between the power force and the fulcrum to be far greater than the distance from the fulcrum to the resistant force.
This is the case in an F1 car, but the force applied to the rocker (that acts as a fulcrum) is the result of two components – the lift force and the perpendicular force that is directed inwards.
Therefore, the angle of the push-rod element plays a relevant role in producing a stiff linkage. Simply put, it needs a dramatically higher load to be applied to secure the resistance. As such, all the assembly elements are very rigid.
This feature has been chosen by almost all F1 teams so as to have a very stiff front-end and to reduce ride-height changes.
How pull-rod suspension compares to push-rod
A pull-rod system, seen predominantly at the rear-end of F1 cars, is a second-class lever. It is softer than a push-rod system and, in recent years, was cunningly used to cope with the sport's high-rake cars.
The rear-end of an F1 car is regularly placed under a high downforce load and, thanks to a softer rear suspension provided by a pull-rod system, will lower into the ground at high speed to both increase the downforce generated by the floor and reduce the drag generated by the car.
This season, with the reintroduction of the ground effect philosophy, the need for pull-rod suspension should be less than in previous years.
However, only two teams changed their suspension layout: Red Bull, notably, and McLaren. The two teams adopted a pull-rod system at the front and a push-rod system at the rear. The question is: does this suspension system swap have any specific relation to the ground effect aerodynamics?
It does, but this change mainly has its roots in improving the packaging of the suspension's mechanical elements. These elements can now be packaged lower at the front-end, lowering the centre of gravity, and higher in the rear-end, moving those elements well above the new Venturi tunnels at the rear of the floor.
It is well known that this season's cars are dramatically heavier than those of the past, with a minimum weight of 798 kilograms. Combine that with the sport's new, slightly bigger wheels, and the cars are less reactive in fast direction changes.
Red Bull and McLaren come up with the same solution
To fight the aforementioned problem, Red Bull and McLaren's decision to run a pull-rod system at the front has placed those mechanical elements as low as possible, level with the bottom of the chassis.
The pull-rod system is, as discussed, softer compared to the push-rod – and so there is an adjuster that modifies the length of the pull-rod lever to reach the ride height desired. The lower the ride height, the stiffer it becomes, as was the principle of the rising rake.
Adopting a push-rod system at the rear means for perfect rear-end packaging of the Venturi channels that now run underneath the floor. By placing the rockers, the dampers and torsion bars above the gearbox case, space is created underneath to have more freedom in the design of the diffuser and floor.
To conclude, the choice made by Red Bull and McLaren to adopt pull-rod suspension at the front and push-rod suspension at the rear, is mainly linked to the aerodynamic concept of their cars.
Furthermore, with the current suspension systems no longer allowed to feature hydraulic heave elements, it would suggest that there is little difference in terms of ride height control between the two systems and thus, with ground effect cars running the same ride height at the front and the back, the dynamic efficiency of the two systems is almost the same.
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