Push or Pull? Badger looks into F1 Front Suspension
Published 15th June 2012 - Written by Chris Kirk
In our last tech feature we discussed front wing design characteristics on modern F1 cars. We looked at how they are built to give these machines the downforce and amazing cornering speeds that make them so fantastic to watch.
This time out we’re moving slightly further back to look at the front suspension, examining just what it does and how its unique properties allow the car to stay just a few centimetres off the ground while maintaining those high speeds through corners.
What does each bit of the front suspension do?
The front suspension components are not very different to those at the rear. Extremely stiff in comparison with your everyday road car, there is very little give in the suspension movement, with around half of the vertical travel caused by the tyres rather than the suspension.
The suspension has to be this stiff to be able to cope with the enormous forces experienced when the car is on track. It also help keep the car as stable as possible to allow the aerodynamics to function. All aero forces, as well forces generated through braking and acceleration, are fed directly through the suspension, which is connected to the wheels and chassis through uprights.
Just think – the suspension (as well as the driver) has to cope with 5Gs of downforce every time the car goes through Copse corner at Silverstone. In the Grand Prix itself the suspension will have to perform flawlessly 52 times – and that’s just one corner!
All the front components are also manufactured to be as aerodynamically efficient as possible, which is why the suspension arms are long and flat as opposed to the comparatively basic, thin looking tubular suspension of the ’80s and ’90s.
The overall components feature two large and extremely strong wishbones at the top and the bottom of the chassis. These are made from carbon fibre with metal rods inserted to allow the wishbones to be mounted to the chassis. The wishbones are then connected directly to the upright on either side and are used to keep the wheels attached to the car.
The other major component is the track-rod, which is usually mounted in front of the upper wishbone on either side. This rod is connected directly to the steering to allow the driver to steer the car.
Lastly, and possibly most important of all, is the push-rod mounted on either side. This diagonal rod is used to control the ride height of the car as well as controlling the overall suspension movement under braking, accelerating and aerodynamic forces.
How do the push rods control suspension movement?
While the push rods on either side connect directly to the bottom of the upright that the wheel is attached to, they don’t connect directly to the chassis like the upper and lower wishbones, but connect to components inside the front of the chassis called rockers.
These rotate the torsion bars, which are mounted lengthways inside the front of the chassis and work as springs and are connected to the dampers (sometimes called shock absorbers).
When the car drives over a bump at high-speed the push rod’s job is to react and keep the tyre in contact with the track surface for the maximum amount of time and for the maximum amount of grip possible.
To do this, the push-rod reacts to the wheel moving upwards over the bump by “pushing” the push-rod in. This in turn causes the rocker to rotate the torsion bar and compress the dampers. The dampers are used to resist, or dampen, any bouncing effect as the push rod and spring/torsion bar react to undulations in the track surface. While the wheel is bouncing around it is providing less grip and increasing tyre wear.
Anti-roll bars are also connected to the rockers. These are then connected directly to the inside of the chassis and are used to generate a faster or slower rate of ‘roll’ (doing this is the easiest way to change the mechanical balance – softer means more rear and therefore less understeer and vice versa).
What if it’s a really bumpy track – won’t teams have to raise the ride height?
A good question. While the suspension components are made as one complete part with no obvious adjustment mechanism, the teams can make slight changes to the push-rods, which are used to control the ride height of the car. Known as shims, these are millimetre-thick inserts that can be placed into the top of the push rod, increasing its length and thus making the car ‘taller’. Increasing the ride height, even the smallest amount, has a profound aerodynamic impact on the car, so ride height is added or taken away as little as possible.
Over the course of the race weekend the team will also have the ability to change the spring rate and camber angle of the tyres (camber is the amount the tyre leans inwards, which helps with turn-in and reduces understeer) although the camber angle is limited to 3.5 degrees by Pirelli.
Push Rods VS Pull Rods
You’ll hear people talking about pull rods as well as push rods somethings – indeed, this season Ferrari has decided to ditch the push rods at the front of the car and instead use pull rods. They’re the first team to try this since the Minardi PS01 way back in 2001, with Red Bull bringing about a revolution of sorts in terms of pull rods being used on the rear suspension in 2009.
In essence, the basics of the pull rod at the front of the car to the push rod setup is exactly the same, just mounted upside down! Instead of the rod being mounted to the bottom of the wheel assembly and the top of the chassis, it’s the complete reverse.
Therefore, if the car reacts to a bump in the track surface like the push rod setup, the wheel moves upwards as usual, but this will pull the push rod upwards rather than pushing it in. This then rotates the torsion bar and activates the dampers, just the same as push rod design, but with these components mounted at the bottom of the chassis at the front of the car instead of the top.
What’s the major gain for having pull rods instead of push rods?
For starters, it provides slightly better aerodynamics: with the top of the chassis now clearer it can provide better airflow to the top of the sidepods, and beyond. As the springs, dampers and other components do weigh a fair few kilograms it also provides a lower centre of gravity (CoG). The lower CoG at the front of the car means that it can help create a more positive front end to corner entry if the car is well balanced overall. Ferrari has also likely done this due to the very high nose on their car for this season, which would have made the CoG higher.
Will other teams follow this approach?
No, not this season at least, as modifying the suspension geometry would take a massive amount of work and time. This could be clearly better spent examining other aerodynamic advances, such as clawing back rear downforce in the wake of the banned exhaust-blown diffusers. Crucially, it would also require a completely new chassis.
It will be interesting to see if anyone does try it for 2013, or if indeed Ferrari stick with the idea. Swapping between push rods and pull rods at the front and rear of the car is certainly not a new concept: in the ’70s and ’80s pull rod front suspension was fairly common due to the very low noses on the cars competing during that era.
As can be seen when you look at the Ferrari, or the above diagrams, the pull rod at the front is at a very shallow angle compared to the push rods. This is what makes pull rods so hard to incorporate into high nose cars. You’re very near the limit of being able to make the suspension react correctly, and as such the pull-rod must be a very strong component. Ferrari likely spent a lot of time and resources making sure the integrity of these shallow mounted pull-rods hold out during a race weekend without any issues.