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This is part two of our couple of videos looking at suspension. I’d recommend watching the
first video first… obviously. But let’s quickly look at where we are so far in how
the suspension is set up on an F1 car. We’re looking at the front end of the car
where the wheels are structurally mounted to the chassis via wishbones and a pushrod
connects the wheel mounts to a rocker inside the front nose.
As the wheel rises relative to the chassis, the pushrod pushes on the rocker, rotating
it around an axis. The rocker is connected along this axis to
a metal torsion bar, fixed to the chassis at the other end so as to force a twisting
motion along the bar, which the torsion bar resists and recoils from like a spring.
When released the torsion bar springs back into its original shape. When people talk
about the front ‘springs’ of an F1 car, they are referring to its torsion bars.
Now, to stop the torsion bar springing back uncontrollably and causing the car to bounce
around, fluid filled pistons are connected to the system via the rocker to absorb the
energies going into and out of the torsion bar.
These are called dampers or shock absorbers, though they are not the only dampening system
on the car. Together, all of this smooths out the violence
of the vertical motion experienced by the wheel so the chassis can remain relatively
stable. Now: bumps and kerbs aren’t the only thing
suspension needs to handle. Far from it. Because all of the driver inputs into the car are
very powerful, the car needs to be able to control the energies across the chassis and
into the wheels. When a car brakes, the centre of mass shifts
forward putting more weight over the front wheels. This will naturally cause the front
suspension to compress and the rear suspension to relax, pitching the car forward.
The opposite is true under hard acceleration. The weight shifts backwards, compressing the
rear suspension, pitching the car back. When a car turns a corner, the centre of mass
shifts to the outside of the car, putting more weight over the outside wheels. In this
case, the car’s outer suspension compresses, while the inside relaxes as it goes light.
The car moving away from its desired platform (which is sort of flat but not quite because
engineers build in some rake for aerodynamic reasons) presents a number of issues.
The first is simply that, due to the cars being so low to the ground you can easily
have the floor or the wings or whatever hit the ground and damage the car. This can be
managed to an extent by packers, which are basically like bumpers inside the suspension
which limits how far they can travel. Another issue is the aerodynamics will behave
less than optimally if you’re rocking the car in all manner of angles away from its
designed position. You want to present the car to the airflow at the desired angle. Things
like rake and wing angles are there for a reason.
Thirdly, when cornering your tyres will roll off their desired camber. I’ve a whole video
on camber, which is technically a part of the suspension setup, but in simple terms
it’s how the tyres are angled relative to the horizontal.
Now you’re probably going to camber in your tyres a little because cornering will induce
this roll in your car. And as mentioned, the weight moves to the outside and loads up the
outside tyre. As such you want the outside, load-bearing,
tyre to present as squarely to the track as possible to maximise how much tread meets
the tarmac to prevent wear, degradation and temperature issues. Part of controlling the
roll of the car will come through the suspension. But let’s start with ‘heave’.
Heave is essentially when both front or rear suspensions are compressed or expanded at
the same time. Like under breaking when the car pitches forwards, the nose is forced down
and the wheels, relative to the car, move up.
This forms a dual compression from both sides of the front suspension.
Now we may not want the front of the car dropping so dramatically. We don’t want the front
wing hitting the ground, we don’t want the rake unsettled, we don’t want the rear wheels
going too light, etc etc. So we can put a heave damper and/or heave
spring connecting the two rockers to resist and control their rotation if both sides try
and compress simultaneously. Now the front drops, the pushrods on both
sides push their rockers inwards, the heave spring resists and absorbs their force, preventing
the front dipping too dramatically and keeps the car stable.
Note that the heave spring only comes into play when left and right both compress against
one another. If the car rolls, it will move freely with the dampers.
Conversely, the outer dampers affect each wheel independently.
So now let’s consider roll. As a car turns the centre of mass shifts to
the outside causing the car to roll outwards. This puts the car in an unfavourable aerodynamic
position, affects mechanical grip and may roll the tyres off the desired footprint.
Part of countering this is the anti-roll bar. In a normal car, the anti roll bar is a wide
u-shaped bar attached at either end to each suspension mount and fixed in the middle to
the chassis. Without the roll bar, the outside, load-bearing
tyre rises relative to the chassis so you end up in this situation with the outside
tyre very high and the inside tyre very low. With an anti-roll bar, as the outside tyre
rises under compression, it pulls its end of the shape up.
As the U-bar is allowed to rotate, this forces the other end of the bar up.
This therefore lifts the other wheel relative to the chassis so the discrepancy is reduced
and the car levels out. The outside wheel lifts, forcing the inside
wheel to lift too so instead of rolling the car stays much more level.
Now, like the torsion bar, this length of metal has some give in it so is allowed to
twist. You can adjust the stiffness of your anti roll bar to dictate how much it resists
rolling forces in the car. Now, in an F1 car, this fairly large unit
has been reimagined into a small U formed of a small torsion bar joining two arms connected
to the rockers. I mean, I say this, but actually F1 teams have been coming up with various
novel versions of the anti-roll bar, but this is the main principle of the design. There’s
some great Craig Scarborough diagrams of some other solutions I’ll link to in the description.
Front Anti Roll Bar Solutions | Scarbsf1's Blog (wordpress.com)
Note that the anti-roll bar will lower the car overall as it balances both sides into
alignment by compressing both. So that’s something to consider in setup.
Controlling roll overall is a collaboration between the anti-roll bar and the outer suspension
and dampers. Both play their part and setup adjustments between the two should find the
right balance in finding the desired roll characteristic of the car.
The rear suspension is fundamentally similar except the rocker assembly is mounted vertically,
allowing for components to be better arranged around the gearbox, power train and crash
structure. Naturally, it doesn’t require the steering
arm either. Setting up your suspension for ideal speed
and handling is a matter of feel for the demands of the circuit and its relationship with your
car design. In general, softer, more compliant suspension
will more ably absorb jolt and bumps and ride the kerbs more smoothly, but will lead to
more roll and pitch and handle more sluggishly Stiffer suspension is more bumpy but has less
roll and keeps the car stable. This can result in less mechanical grip but greater handling
sensitivity and responsiveness. So precise driving between barriers may benefit
from some stiffness, if it can handle the natural bumps of a street track surface.
A fast, ero heavy track may prefer the stability of a stiff setup, whereas a twisty track with
slow to medium speed corners w ill benefit from a softer setup to squeeze more mechanical
turning grip out of the car. And, of course, this isn’t just a matter
of sliding the car setup between soft and stiff, but combining the spring stiffness
of the torsion bar with the compression and expansion characteristics of the dampers and
the heave spring, with the give of the anti roll bar. Everything works together and affects
the other. There are many innovative and clever inventions
within the suspension systems of F1 cars and these videos have just outlined the basic
common structures. Over and again, teams have sought to subvert
the norms to rearrange the layout, bend the regulations and eke out a more controlled
performance from the suspension. Hopefully though, these videos will give you
a solid base from which to understand further talk of suspension throughout F1 weekends.