A big talking point of Formula 1 car design is push-rod and pull-rod suspension.
But what is the difference between them, and why is it so important?
What's the difference between push-rod and pull-rod suspension?
An F1 car’s suspension has an upper and lower wishbone – triangular-shaped carbon fibre bars that absorb the shock from the road – which essentially connects the chassis to the wheels.
Between the wishbones, both at the front and rear, is a suspension rod – either a push-rod or a pull-rod – that connects the wheel to a horizontal torsion spring. The torsion spring stores and releases energy, while twisting when force is applied to it, and that helps to keep a car stable over bumpy surfaces.
A push-rod mechanism sits high up on the chassis where a diagonal rod then connects it to a low point of the wheel. So, over bumps or kerbs the wheel pushes on the torsion spring and that causes the push-rod to go upwards and towards the chassis.
That is the opposite to a pull-rod. A pull-rod mechanism sits low on the chassis where a diagonal rod then connects it to a higher point of the wheel. This means every time the car hits a bump or kerb, the wheel pulls on the torsion spring which causes the pull-rod to go up and outwards from the chassis.
Both configurations have many advantages and disadvantages. It simply depends on what a team wants, because the suspension must fit the aerodynamic concept of the whole car as it plays a role in directing airflow towards the sidepod and other areas.
For example, a pull-rod has better weight distribution because everything is run closer to the ground as heavy components are mounted towards the bottom of the chassis. This is especially important on ground-effect cars because the lower centre of gravity helps to reduce drag, aid cornering ability and arguably provide a better aero performance.
On the other hand, a push-rod is more practical as its local aerodynamic footprint is more favourable, which means the immediate aero around the suspension is cleaner.
Furthermore, having the suspension parts higher on the chassis means it is easier for mechanics to work on the car, because if the front suspension has a pull-rod layout it makes the area quite cramped and sometimes the floor needs to be removed for certain parts to be accessed.
The push-rod can provide better stability, while it is also cheaper. Although a push-rod may work better for one car, it might not for another and vice-versa with the pull-rod – sometimes, though, it comes down to deciding on aerodynamic and performance gains against cost and practicality in the ground-effect era.
F1 teams can also split the use of both configurations by fitting a pull-rod at the front and push-rod at the rear or vice-versa.
Which F1 teams use push-rod or pull-rod suspension on their cars?
Red Bull and McLaren have been the only teams to use a pull-rod configuration on its front suspension for the past two years of ground-effect cars. But Sauber and RB have become the next teams to use a pull-rod configuration at the front for the 2024 season.
The Swiss outfit has made extensive changes after finishing next-to-bottom in the 2023 constructors’ championship, while Red Bull's sister squad has taken a development direction similar to the world champions.
What will help Sauber's transition is technical director James Key, who joined the team from McLaren in September 2023 even though it had already decided on a pull-rod before then.
He believes the aero gains of a pull-rod configuration far outweigh the practicality problems it presents because “it is all about managing your front tyre wake” – a turbulent air flow around the car.
Key also thinks that more teams will follow suit as “fundamentally, it's the right thing to do” and there is probably no better example of that than Red Bull. Using a front pull-rod configuration, Red Bull has won the past two championships with rounds to spare – including winning 21 of 22 grands prix in 2023 – and its suspension played a pivotal role in that.
A pull-rod suspension has helped Red Bull to have a sharp front end which is exactly to the liking of world champion Max Verstappen, and the stiffness that presents gives the team a big advantage in the ground-effect era due to its low centre of gravity.
But Red Bull uses a push-rod configuration on its rear suspension which is in line with most of the grid because Key thinks the debate “at the rear isn't a talking point really. It is mechanically better to go push-rod for various packaging reasons” as it can help to narrow the gearbox and alter the floor shape, which opens up downforce-producing performance at the car’s rear.
In 2024 eight teams will be using a push-rod configuration at the rear as opposed to five from 2023, because Mercedes and its customer outfits – except for Williams – have made the switch.
Ferrari will be using a pull-rod configuration at the rear in 2024 as technical director Enrico Cardile explained how its rear suspension “is a bit different” to the Scuderia’s rivals, particularly Red Bull, so it is not as well-suited to a push-rod structure.
Williams, meanwhile, decided to not go in the same direction as Mercedes for various reasons one being that there is a cost cap benefit in sticking to last year’s parts.
|
Team |
Suspension choice in 2024 F1 season |
|
Red Bull |
Pull-rod front, push-rod rear |
|
Mercedes |
Push-rod front, push-rod rear |
|
Ferrari |
Push-rod front, pull-rod rear |
|
McLaren |
Pull-rod front, push-rod rear |
|
Push-rod front, push-rod rear |
|
|
Push-rod front, push-rod rear |
|
|
Williams |
Push-rod front, pull-rod rear |
|
RB |
Pull-rod front, push-rod rear |
|
Sauber |
Pull-rod front, push-rod rear |
|
Push-rod front, push-rod rear |
History of the push-rod and pull-rod suspension in F1
Push-rod and pull-rod suspensions date back to the 1960s and ‘70s, as a push-rod was introduced by legendary car designer Colin Chapman, who founded Lotus.
He used an inboard suspension on the Lotus 21 that finished second in the 1961 F1 championship.
Brabham’s Gordon Murray then introduced the pull-rod configuration on a BT49 in 1979 and it was a revolution. This is because the pull-rod was much more flexible than the archaic hydro-pneumatic suspension which was used at the time – meaning a car’s centre of gravity was lowered causing an improvement in performance.
Over the coming seasons, Nelson Piquet won the 1981 drivers’ championship for Brabham, while other teams also attached a pull-rod suspension. However, the pull-rod suspension became much less used in the 1990s when a minimum ride height rule was introduced, which meant teams needed a higher centre of gravity.
It returned to F1 in 2009 under revised regulations where the diffuser was moved rearwards. So, with Red Bull’s use of low sidepods, Adrian Newey believed attaching a pull-rod would help lower the RB5’s centre of gravity allowing for cleaner airflow to the car’s rear – and it worked.
Despite only using a single diffuser compared to Brawn’s double diffuser, Red Bull came very close to beating the eventual world champions with the diffuser simply proving to be the difference maker.
So, a double diffuser was attached to the RB6 alongside a pull-rod suspension and 2010 started a run of four consecutive double world championships for Red Bull and Sebastian Vettel. Red Bull started a trend, as 2011 saw 10 of 12 teams use a pull-rod before Ferrari and Sauber joined the majority the following year.
Ferrari became the last team to use a pull-rod suspension for several years, as the configuration featured on its SF15-T in 2015 before push-rods dominated once again.
But the reintroduction of ground-effect cars in 2022 presented the opportunity for pull-rod suspension system to return because of what can be gained by running closer to the ground.
