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Let’s discuss an F1 car’s suspension. Why it’s needed, what it does and how it
works. To do that we’ll need to go over the basics
of suspension first - the fundamentals of what it’s trying to achieve and how that’s
designed into the tight body of an F1 car. That’s what we’ll be covering in this
video. Then in a second video we’ll go into more
details and explain how and why an F1 car balances and tunes forces across the car with
dampers and anti-roll systems and such. So, let’s start at the very beginning.
The only thing connecting an F1 car to the track it’s driving on are the wheels.
So all the steering, braking, aero and power are all dependent on how all those inputs
are translated into forces through the tyres into the track.
Ideally we want the tyres planted properly at all times, as squarely as possible with
as much tread as possible meeting the tarmac. We want the right amount of weight distributed
across the four wheels to meet the load demands of cornering, braking and acceleration while
keeping the aerodynamic platform of the car relatively stable.
A huge amount of this can be controlled and regulated by the suspension.
Let’s imagine a car where the wheel axles are fixed rigidly to the car chassis. The
wheels are free to rotate, obviously, but the axle and the car essentially move as one
fixed unit. If the car is travelling along a smooth surface,
all is perfectly fine. But if there are bumps in the track, the wheels
will ride those bumps and be violently kicked up and down.
As the car and axles are fixed together the car chassis itself will be kicked around exactly
as violently as the wheels. The front and back end will just match the vertical trajectory
of the wheels. You can imagine how this could be more than
a little discomforting to the person inside but also puts a lot of force through the chassis,
potentially causing damage. On top of that, with the car bouncing around
a lot, reacting to these bumps (which you could imagine as a bumpy track or the brutal
kerbs around corners) will cause the tyres to load and unload as they leap from the track
surface. This reduces the handling of the car as you
can’t reliably input your steering, acceleration and braking through the tyres if they are
not properly planted to the track. So, instead let’s start by placing a spring
between the wheel mounting and the chassis mounting.
A spring is cool because it absorbs energy via compression. If you load a force along
a spring it steals the energy into changing the shape of the spring, converting it into
potential energy. This is similar to elastic which stores energy
via extension. Springs store energy via compression. So the spring reduces the force going into
the chassis by absorbing it into its compressed shape.
So while the wheel may still be kicked forcefully upwards by a kerb, the chassis now sees less
of that upward energy so reacts more mildly. But a spring, like elastic, desperately wants
to return to its original shape. It will store the energy as long as it's held compressed
- but when released it will extend with some force!
This can result in the car ending up bouncing wildly as the spring absorbs and then releases
compressed energy. This is also bad for handling and driveability
as the car is now unpredictably bouncing over the track after every bump.
The problem is almost all the energy is still in the system, you’re just releasing it
into the car in a different way. What we need to do is actually get rid of this energy somehow
before it gets to the chassis. And this is where we introduce dampers to
dissipate the energy. We can add a shock absorber to the spring
in the form of a hydraulic piston. So imagine the top and bottom mounts of the
spring are now connected via a piston filled with a kind of oil.
There are small holes in the piston itself and between inner and outer chambers which
will allow a limited flow of fluid as the piston moves up and down. But this takes a
lot of effort. You can imagine how hard it is to push and pull the piston through this
fluid. So the energy in compressing and releasing
the spring is being lost working this piston through the fluid so we won’t see a dramatic
compression and extension ba-doingggg of the spring.
And you can design and adjust dampers differently to change how easy it is to either compress
or extend the spring. You might want an easier compression rate than relaxation rate depending
on your setup needs, for example. Shock absorbers are velocity sensitive - this
means that the faster you try and force them, the more they’ll resist, which is incredibly
useful for working a violent kerb versus a gentle compression of the car.
So now the ride of the car is smoothed out. And this is especially important in a racing
car for both handling and aero stabilisation. As the chassis and its components are fine
tuned aero surfaces, having the car move around the airstream in a bouncy chaotic way would
undo a lot of the good work put into its aerodynamic design.
So keeping the platform of the car as stable as possible maximises its aerodynamic efficiency.
Ok so all well and good so far, but you may be looking at this graphic and back at an
F1 car and think ‘well this looks nothing like F1 suspension. I’ve never seen a spring
in my life, just a bunch of carbon fibre arms.’ And you’d be right. While there did indeed
used to be traditional spring setups on an F1 car that look quite similar to what you
might see under your Peugeot 106, these have all been converted into tighter, well-packaged
solutions inboard. So coming off the front wheel mount, you’ll
see six arms joining it to the chassis. Four of these are just the wishbones that
essentially structurally connect the wheel to the car.
One is the steering arm or track rod. This moves horizontally through the chassis and
pushes and pulls the wheel mount around the pivot point supported by the wishbones.
Lastly is the pushrod or pullrod, depending on your setup. Up front, basically everyone
uses a pushrod system so let’s start there. The pushrod is connected to the wheel mount
and enters the chassis through a hole and connects to a rocker - basically just a mounting
allowed to rotate around an axis. As the wheel is raised relative to the chassis,
the rod pushes the rocker, rotating it. Hence the term ‘push rod’. The rod pushes against
the rocker. The alternative solution, favoured at the
rear of the car currently, involves mounting the rod and rocker such that the wheel rising
will pull the rocker around its axis. This is a pull rod system.
But we’ll stick at the front with the push rod for now.
So the benefit of this rocker is that it translates the linear motion (back and forth here) into
a rotational motion. So now we can work the suspension in any direction we like off this
rocker. Great for packaging. Our dampers can now slot in nicely here, for
example. So the jolt of the wheel comes in this direction
but is damped in this direction, through the rotation of the rocker.
Also note that because we can mount different parts of the suspension at different distances
from pivot point we can magnify the motion into the piston of the damper.
By mounting the damper further from the pivot of the rocker than the push rod we can translate
small motions in the pushrod into long motions in the damper, giving us greater fidelity
in controlling damper characteristics. Now the ‘spring’ in the front suspension
isn’t a spring at all but a torsion bar. A torsion bar is simply a metal rod made to
a particular material characteristic. One end is fixed rigidly to the rocker so
it turns with the rocker. The other end is fixed rigidly to the chassis so it doesn’t
rotate at all. As the pushrod rotates the rocker, it forces
the torsion bar to twist - something the torsion bar will resist.
And, when released, the torsion bar snaps back to its original shape. So functionally
it’s identical to a spring in how it absorbs and released energy but it is lighter, smaller
and more flexibly packaged. So that’s your very basic suspension setup
so far. Hopefully you can see how F1 cars absorb and control forces from the wheels
so as not to upset the car. But it gets more complicated than that as
teams will want to have greater control over distribution of forces over the four wheel
of the car to maximise the handling of the car. So in the next video we’ll go deeping
into systems like anti roll bars, heave dampers and systems that help optimise the setup of
the car.