Earlier installments of Build128 have taken you through, step-by-step, in how we perform some of the processed we undertake as we construct our cars. From the tub chassis, to the exterior panels, to the preparation and paint stages of the build.
As with our last instalment – the Koenigsegg engine – we’re going to talk in coming instalments about why we do things the way we do, rather than concentrating on how. It’s one thing to tell you that a guy screws a part in to point ‘A’ on the chassis. It’s a different thing, and a more important thing, to tell you what that part does and why it exists.
To our subframe and suspension, then…..
At this point in production, the panels have been removed from the car at the end of Station 2 and are sent to Station 3/4 for preparation, paint and polishing. While all that’s happening, the tub chassis moves along to Station 5, at which point the chassis is prepared to receive the engine, gearbox and front/rear subframes and suspension.
Technicians on Station 5 prepare the chassis for the subframe by fitting a lot of the ancillary items to the chassis. In the photo below, you can see that heat-shields have been fitted, along with the battery and other fittings.
Station 5 also sees the installation of a lot of the hoses required for both the cooling system and the HVAC system, as well as much of the wiring that needs to be installed in the car. The wiring looms are all designed and made in-house by our electrical team.
While that work is being done directly on the chassis, Berne is at another station building our Agera RS subframe. Berne is one of our longest serving employees and has actually been working in our Angelholm building longer than we have. He started here over 40 years ago working with the Air Force when our building was a Swedish Air Force base.
Our subframe is made locally in Sweden and comes as a basic structure when it first arrives in the factory. Berne’s work involves fitting the gearbox, engine, steering, suspension and brakes to the subframe so that it can eventually be attached to the car.
You can see the front subframe and suspension being offered up to the chassis prior to fitting in the photo below….
So let’s look at the components we’re talking about, because they are absolutely critical in ensuring that the Agera RS can get all of its massive power to the ground, and keep it there no matter whether it’s on a straight or charging through a corner.
For the rear of the car, we’re going to be focusing on parts you see in the highlighted area below…..
The wishbones we use are central to the extraordinary handling we’re capable of extracting from our cars.
Highlighted below is the under-side view of our front wishbones.
Our wishbones are made according to our own specification and welded by CP Autosport in Germany, who do similar components for many other high-end hypercars and racing teams. The wishbones and other framework are made from seamless chrome-molybdenum steel tubes. Chrome-molybdenum is the strongest, lightest material available and the best-fit for this purpose (see below for why we don’t use carbon fibre for this).
One of the keys to our superb handling is that our wishbones are very long. They’re much longer than those in use by any other manufacturer for road vehicles. Long wishbones mean that we have much less track-width deviation during wheel movements, which allows us far greater stability in the chassis during wheel movement with less sideways scrubbing of the tyres.
What does that mean? It means that we get much greater predictability and less tyre wear for the same amount of grip.
Rear wishbones, top view, below…..
Suspension systems allow for up and down travel when the car goes over bumps. You do want this up/down travel but you do not want the system moving forward/back at all. The wishbones are basically a parallelogram and the longer you have them, the less in-out (front/back) movement you get during normal suspension travel.
Most road cars with wishbones have very short wishbones because they’re compromised by a lack of space. There simply isn’t room for them. They need the space that the longer wishbones would take up for equipment or other mechanical parts that they need to accommodate in that area of the car.
At Koenigsegg – with great thanks to our compact V8 engine and gearbox for this – we have been able to package the car in such a way that we can have really long wishbones at both the front and the rear. It’s very tricky to produce long wishbones because they fan out at one end. When they’re long, they have to be wide. That width takes up more space than some engineers want to give them. Ideally, they want to pack mechanical parts in that space.
Prioritising our wishbones during the design stage gives us the best foundation possible for race-grade handling in our road-going cars.
The wishbones connect at the outer edge to the uprights, which house the wheel bearings. As our wheel bearings are super-sized (see below), our uprights are also very big.
Being such a large piece, the uprights could, theoretically, be quite heavy. They’re not, though.
Our uprights are hollowed out where possible to ‘add lightness’ but this is done in such a way so as to ensure that they’re still strong enough to accommodate the wheel bearing and add stiffness.
Our Koenigsegg wheel bearings, at 240mm, are the largest used in the automotive world today.
Our wheel bearings are ball bearing units and with such a large bearing, you have more rollers inside the unit. Some may think that this means more friction but actually, the opposite is true. Each ball bearing has less load, so it suffers less friction. That means more speed, with less heat. In fact, if you’re going to be travelling at 400+ then you really need a bearing unit this size to carry the load without intolerable stress and heat.
The advantages of having such a large bearing:
1. less heat and all that comes with it: less resistance, less chance of fatigue and less fuel use.
2. The bearing, because it’s so big, is stiffer than a smaller bearing. Combined with the large upright, the bearing compliments the long wishbones by completing the job that they start. The wishbones are designed in such a way as to minimize lateral movement and maximize predictability. It would be pointless to design such a system and then give away those gains with an undersized bearing/upright.
The whole rear system is designed so that the wheel itself will do exactly what we want it to do. It’s all about getting the motion of the wheels to work as designed. You use clever and robust design to abolish any potential weak links.
That includes the wheel itself, by the way. As you know, most new Koenigseggs that we build are fitted with carbon fibre wheels, which not only reduce weight but are extraordinarily stiff, further enhancing our handling capabilities.
Here’s a practical example of how stable our car is because of the suspension design – being able to accelerate from 0-300 and back to 0 with no hands on the steering wheel.
The car is extremely stable at high speed because of the suspension geometry with no lateral movement allowed without steering input (NB, the times when you see Robert touch the wheel are purely due to the camber on our runway, which he’s at the edge of)
In some of the places where you might expect to find regular bushings or even rose joints, we have chosen to use needle bearings. This increases the stiffness and strength of the suspension system and reduces stiction and hysteresis (the tendency for the condition of the part to be shaped by its use. ‘Stiction’ is the friction that tends to prevent stationary surfaces from being set in motion).
Still, the needle bearings work very well with our long wishbones, adjustable shock absorbers and suspension geometry to provide a very comfortable ride at road speeds and pin-sharp handling at track speed.
The key to this comfortable road handling is weight – or lack of it, to be more precise. We have a very light car, of course, but more specifically, we have extremely light carbonfibre wheels. Those light rims, combined with our large, friction-reducing wheel bearings and long wishbones mean that whenever you go over a bump, the suspension moves very quickly to adjust for that bump. There’s very little travel required for our long wishbone to adjust for that bump. There’s very little weight or inertia for the system to fight against. The result is a super responsive suspension system that adjusts extremely quickly to road conditions while still maximizing both the comfort level and the handling characteristics experienced by the driver.
In addition, we use O-rings at the ends of these needle bearings so that they do have a little bit of ‘give’ in one direction but remain very stable during rotation. Just as you want them to be.
Most of you would have heard of, or seen, an anti-roll bar fitted to a car. They usually look like this:
The anti-roll bar as developed by Koenigsegg looks a little different. It’s the Z-shaped item highlighted in the image below:
The basics of this Koenigsegg solution were developed right from the first vehicles we ever made. It’s another scenario where Christian looked at a traditional part and wondered if it could be done better, smaller, lighter.
The Z-shaped anti-roll bar on the Agera RS only has one pivot point, instead of the two pivot points on a traditional anti-roll bar. That reduces friction and therefore increases accuracy and response.
We use it on both the front and rear of the Agera RS.
The central section of the anti-roll bar is steel. The two outer sections are carbon fibre rods. When the wheel wants to travel, the rod pushes against the central steel section, which gives a little bit of flex between the end and the pivot point but is countered both by the nature of the material and forces pushing from the other side.
It’s still a torsion-based system like a traditional U-shaped bar but the materials, the lack of drop-links and the angles used in the geometry of our anti-roll bar make it a much more progressive system. And if you compare the materials using the two photos above, you can see that our anti-roll unit is super-light compared to a traditional bar. This means we get a more accurate, faster anti-roll bar at only around one-fifth of the weight of a traditional U-shaped bar.
Our dampers are made by Ohlins, a Swedish supplier, but they are not the regular Ohlins dampers that you can buy off the shelf.
When the dampers arrive out our factory, the control module is picked apart by our electrical team and new electronic controls are installed to assist with bump and rebound. The circuit board and processor are our own design and work in such a way that we can actually communicate with the car, either directly or remotely. That way, we can gain information about the performance of the car. For example, at a racetrack, we can analyze the car’s performance and reprogramme the dampers to make them perform better. Such analysis can be done on the spot by the owner, or it can be done online by Koenigsegg at the factory, regardless of where in the world the car is located.
Whilst there are many ‘active’ damper systems available in the automotive world, there are none as advanced as this, with separate electronic ‘on-the-fly’ controls for both bump and rebound and the ability to communicate directly with the mothership for analysis and programming.
Each corner can be controlled independently via these dampers for ride height, bump and rebound. If you’re heading into a corner on a track, for example, the system can be set to pre-load the damper half a second before that corner to provide the best grip prior to the car receiving steering input. It’s a lot of setup work, but it’s all possible.
The primary reason we have the ‘Triplex’ third damper on the rear of our cars is to provide an anti-squat element to our suspension setup.
Squat is what happens when you take off under hard acceleration – the rear end of the car wants to dip down, or squat, because of the physical forces placed on it.
In the front of the car, the same phenomenon under heavy braking force is called ‘dive’ and we counteract this by mounting the top wishbone at an angle instead of mounting it completely horizontally (levelled). This creates an anti-dive geometry that counteracts the forces that make the nose want to dive under brakes. Again, it helps that we have such long wishbones, too.
We don’t have such an angle in the rear, however.
We didn’t need it, initially. Our suspension setup handled our power and grip requirements at lower outputs simply because of its inherent good design quality. We developed some ‘squat’ issues when we started to build cars producing over 1100 hp, however. Squat provides good rear-wheel grip on hard acceleration but it can compromise handling at the front end of the car and therefore has to be managed.
This is the scenario under which Triplex was invented.
When you take off under full power, the rear end wants to squat down, which means the rear wheels want to ‘rise’ a little, in relative terms, compared to their usual position in relation to the chassis of the car. This action compresses the shock absorbers as the rear wishbones try to lift.
The Triplex rear damper acts against this tendency, providing resistance against ‘squat’ (both dampers compressing at take-off) but doing nothing during regular single-sided compression of the dampers (e.g. during cornering). The Triplex damper also counteracts the anti-roll bar when driving straight on an uneven road, but does not work against it while cornering. This actually increases comfort and grip.
A FINAL THOUGHT……. SUSPENSION AND THE COMPROMISE?
One of the usual things about designing a car is that there always seems to be an element of compromise involved. Things have to be balanced, which means that one element of the car might not be as extreme as you would like it to be because that particular element has to be balanced against the capabilities of, or budget for, other elements.
For example, a manufacturer might want to make a ‘spider’ version of its car by introducing a removable roof panel. Potential compromises include poor NVH, increased chassis flexibility, or maybe even the loss of space after creating storage for the roof.
For high-end sports car manufacturers, the ride/handling of the car cannot be compromised so allowing increased chassis flex is off the table.
Companies want to create a wonderful driving experience, which means they’ll put in the work to maintain excellent NVH standards.
The usual compromise, then, is that the manufacturer will not re-engineer the car to allow space for storing the roof on-board. The owner will, therefore, have to make a decision about removing their roof before they leave home because there’s nowhere to store it if they remove the roof mid-journey.
The customer has to accept the compromise.
All Koenigseggs have a removable roof. We have engineered our cars so that there’s no loss of chassis stiffness, there’s no loss of comfort AND we even have space in all of our cars (except the One:1) for the roof to be stored on-board.
So where’s the compromise?
If there’s a compromise to be identified, it’s one that affected the company, not the customer. Our compromise lies in the fact that our front subframe and suspension took two or three times as long to develop compared to what it might have if we hadn’t been dedicated to storing the roof on-board.
One of the additional benefits of doing this is that our front suspension had to be designed and packaged much lower than usual. That means we have a lower centre of gravity than what we might have otherwise had, turning a potential compromise into a real-life benefit that improves the driving experience while giving the owner more flexibility in how they use the car (roof on/off).
This is typical of the Koenigsegg way of thinking – don’t accept a compromise that will negatively impact the performance of the car. Always commit what you need to in order to succeed.
A FINAL THOUGHT II – Why not a carbon subframe and wishbones?
Theoretically speaking, it would be possible to make our subframes and wishbone suspension from carbonfibre instead of chrome-molybdenum steel.
So why don’t we do that?
The choice of materials comes down to a cost/benefit decision. For us, and for our customers, that decision was settled in favour of chrome-molybdenum.
The weight difference is not as significant as you might think because if we were to use carbon, we would need metal inserts all over the subframe for connecting pieces. It would be much more complex to manufacture and therefore much more expensive for our customers. It’s also much more expensive to repair if something goes wrong (i.e. a serious crash that shatters the carbon).
The chrome-molybdenum that we use is relatively easy to work with for complex structures and we can make it very predictable in its response to stress, which is important when it makes up part of your crash structure and has to have deformation zones designed into it, etc.
Using carbon fibre for our wheels is also very expensive and very complex, but it results in at least a 30% decrease in unsprung rotational mass. That’s a huge, real-world performance benefit; the performance gains are so big that it makes the investment worthwhile.
The performance gains to be made from the use of a carbon subframe and suspension are far less and the costs to the customer – for both initial manufacture and repair – does not make good sense from our perspective.