The Art of Setup Building, Part 7: High Downforce Cars are Weird

 Suspension systems, corner springs, 3rd springs, dampers, packers and anti roll bars

Last time out, we learned that setting ride height just right can net so much downforce and so low drag that any mechanical grip concerns are dissipated. However, if we were to just set the ride heights to hit the ideal points during corners, the car would bottom or stay too high up, If we hit the ideal rake down the straights, we would be losing downforce around corners. To be able to properly setup the amount of ride height we want during during different points of the circuit, we need to tune the Suspension. Now, if we simply looked at the Springs setting ...

We can see the Ride Heights, which I've explained already. We also see a TON of adjustments. And there are EVEN MORE, since we also have Dampers and Anti Roll Bars to deal with. Don't fear, however. This is simpler than it looks. Let's start with the obvious.

Note/Tip: We will be running symmetrical suspension setups. Asymmetrical setups can be useful in the right track, but aren't strictly necessary. In a future chapter I'll talk about them, but for now stick to symmetrical suspension system setups. 

Corner Springs

About 90% of all setup guides start talking about these bad boys. In a high downforce car, they are bit of a set and forget setting, but let's talk about why.

So, you want the tire to stay in contact with the road. That's the mission. You could make the suspension system solid and that would solve the issue. The problem would be that anytime you hit the smallest road irregularity, the car will choose violence. Too quick an input, violence. Stiff suspensions tend to transfer loads quickly and erratically. Tires do not like being loaded quickly and erratically and they'll respond by outputting inconsistent grip levels. The result, car chooses violence against the driver. We can't have that.

Instead, cars use springs on each corner to keep the tire on the road while suppressing aggressive inputs. Now tires will get loaded slowly and in a controlled form, this makes them happy. F1 cars don't use your typical springs. They actually use torsion bars, but they accomplish the same role so I'll call them springs.

So, we want as much grip from the tires, which usually means we need a soft suspension. However, net grip isn't helpful if the car is taking 6 days and 9 hours to enter a corner. A suspension can be so soft that the grip gains disappear because the suspension takes so long to transfer the load that the car takes a while to start responding. So we want some stiffness in the suspension. And not only that, but too soft of a suspension will allow the car to reduce it's ride height so much that it bottoms out down the straights.

If a suspension system was only composed of the 4 corner springs and their dampers, they would have to control the car's handling on their lonesome. That means controlling the car in roll (as in body roll, side to side), in pitch (as in braking and accelerating, front to back) and in heave (as in up and down). To do that the springs should be so stiff that the tires would hate us, or so soft that there would be no control.

So, instead of leaving the corner springs on their own, we have other methods to get the suspension working in the way we want it to. Most race cars are equipped with anti roll bars, which will handle the body roll control. That leaves the springs to control the pitch, heave and the tires themselves. Still quite a bit, but it is less now. This would be the typical race car setup, which is perfectly fine.

However, F1 cars are equipped with a 3rd spring, also called heave spring. I'll talk about it later on, but the 3rd spring handles all heave and pitch duties, leaving the corner springs to deal with making sure the tires keep touching the road.

We can use corner spring rates to alter car behavior in anyway we please, Generally speaking, stiffening up an end of the car will increase that end's responsiveness but will decrease grip. This doesn't increase the other end's grip, but it does make it more stable. Softening an end of the car will increase potential grip, but it will be more sluggish in response. The other end might feel a bit more unstable.

Those effects can be used to reel in certain behaviors in combination with other settings, like front wing angle. For example, we might have a car that is oversteery when riding over kerbs. What can be done is using a stiffer front end, and adding front wing to compensate for the slight loss of grip. The car will be more stable, without losing rotation.

In fact, when talking about front end v rear end corner spring stiffness, the general consensus is that the front should always be stiffer in high performance, rear wheel drive cars. This gives the front end more responsiveness, and allows the rear end to stabilize quickly. In fact, in modern times, teams don't use rear corner springs at all. Just an Anti Roll Bar and 3rd spring. It is a technique that we can apply in current times.

Summary

• On F1 cars, Corner Springs are used to adjust the handling of the car, specially over rough surfaces and kerbs.
• A stiffer suspension makes that end react quicker and be less affected by ride height changes. Mechanical grip might suffer.
• A softer suspension makes the end have better grip. Tires prefer softer suspensions. However, there's more ride height changes and the end might respond slowly.
• Generally, the front end should be stiffer than the rear, to stabilize the rear end. This is just a tip, it can be broken with caution.
• Generally speaking, the whole range is an option in terms of spring rates. However, rear rates over 200 N/mm are quite risky.
• The current trend is to minimize rear spring rates and use quite stiff front ends. With an appropriate setup, this is effective.
• If in doubt, just leave them alone. There are more settings to improve the handling.
  

3rd/Heave Springs

As mentioned before, the 3rd springs control all things pitch and heave related. They have a simple objective: keep the car at a stable ride height.

Let me detail it by parts. As we know, the front wing needs to be as low as possible, but we don't want it sliding on the ground, or even touching it if we can help it. That's what the front 3rd spring is for. We can make the front as stiff as necessary to keep the front off the ground, while keeping the corner springs soft enough to deal with bumps, kerbs and handling concerns. While the 3rd spring has a slight effect in cornering behavior, the effect is so low that it can be ignored.

As for the rear, it is a similar story for 2 problems. We need to optimize the suspension to stay high enough for downforce and low enough for drag. That means we can stiffen or soften the 3rd spring until we hit the ideal ride heights. It won't be perfect, but we have more tools to deal with that. The rear 3rd spring also has an effect on grip under acceleration, however a properly balanced car setup shouldn't have to worry about that.

Summary

• Easier to adjust than the corner springs yet more influential to our F1 machines, the 3rd spring's objective is to control ride height changes at all times. They have no control over body roll.
  
• A stiffer 3rd spring reduces the ride height changes at that end. This means that end of the car won't lower as much as it used to, which is ideal for our front wings and diffusers. However, they might reduce mechanical grip, though this usually isn't a concern.
• A softer 3rd spring allows ride heights to change more at that end. Downforce or inputs such as acceleration and braking will have more of an effect now. This can be good, depending on our objective. This also increases mechanical grip, but that shouldn't be a primary reason to change the 3rd spring.
• If in doubt, assuming front ride height is at the lowest it can be, stiffen this to 100 N/mm on the front and 150 N/mm on the rear. This is not optimal, however. There's a reason why telemetry exists.

Packers and Bump Stops

They are in the incorrect order in the title, but I must talk about Bump Stops first before dealing with packers.

A natural problem that occurs with high performance cars, specially those running high downforce, is that the suspension might run out of travel. This means it can't move downwards anymore. This can heavily damage the suspension, and even if it doesn't the corner springs will act as if their rate is infinite, and we know what happens when our corner springs are bricks. So instead, suspension system designers add what's known as a Bump Rubber or Bump Stop.

A Bump Stop is a progressive spring. Linear Springs, like the Corner Springs, 3rd Springs and Anti Roll Bars, behave in a constant way: You compress them a certain amount, and they output a certain force. Duplicate the compression, and the force duplicates. Progressive springs aren't constant. If you duplicate the compression, the force will be significantly higher. While originally designed to prevent the suspension just running out of travel, engineers quickly realized that the progressive characteristics of the Bump Stop makes them useful for high downforce cars. However ... we can't usually hit the Bump Stops unless the suspension is nearly fully compressed, and by the time we hit them they can't do their job of stopping the bottoming. That's when Packers come into play.

Packers are a solid spacer fitted to the suspension system. Their objective is to make the suspension hit the Bump Stops earlier than usual. If we set the packers correctly, we can have optimal grip in the corners, while running a soft suspension system that will stiffen up as the floor and ground get closer.

We have Corner Spring Packers and 3rd Spring Packers. Generally speaking, the Corner Spring Packers are the most effective way to control ride height, as they'll have a bigger effect over that end of the car. However, remember that if the Bump Stop gets engaged, the suspension will start stiffening up,, which can cost us grip when we needed it. The 3rd Spring Packer is a bit less effective, but also has much lower effect on handling and is the preferred option to control ride heights.

We are now left with four options to control ride height.

• Low packers, low 3rd springs: Usually not recommended. Will keep ride heights low, but bottoming will be common.
• High packers, high 3rd springs: An option on high speed, high downforce tracks. Will keep the ride heights high and controlled, and minimize bottoming. The suspension will feel stiffer, increasing response. Good option for the front end.
  
• Low packers, high 3rd spring. An option on low speed, high downforce tracks. Will keep the ride height high, preventing bottoming from becoming a possibility. Mechanical grip will be fantastic.
  
• High packers, low 3rd springs. The go to option for the rear end at high speed, low downforce tracks, will minimize bottoming while allowing that end of the car to move as needed.

To close out, we need a quick way to know when we will hit the Bump Stops. The answer is simple, with no packers, the front end will hit the Bump Stops at a Ride Height of 5mm. The rear will do so at 10mm. Every mm of packer will add will increase the Bump Stop Height, the Ride Height at which we'll hit the Bump Stops. So, using the image as an example:

• At the front we would hit the Corner Packers at 15mm Ride Height (10mm Packer + 5mm Bump Stop), and the 3rd Spring Packer at 10mm Ride Height (5mm Packer + 5mm Bump Stop).
•  At the front we would hit the Corner Packers at 22mm Ride Height (12mm Packer + 10mm Bump Stop), and the 3rd Spring Packer at 15mm Ride Height (5mm Packer + 10mm Bump Stop).

Summary

• Packers are an alternative way to control ride heights, as well as a quick way to stiffen up the suspension.
• Increasing the Packers will engage the Bump Stops earlier, which will stiffen up the suspension the more they get compressed. It will increase Ride Height control, but Mechanical Grip could suffer.
• Decreasing the Packers will allow the suspension to move more freely, favoring Mechanical Grip, but sacrificing aero control.
• If in doubt, remove all Corner Packers, and increase the Rear 3rd Packer to 20mm.

Dampers

Might as well deal with everything in regards to ride height control. Dampers are seen like this mystical, magic device that affects handling, but it isn't that scary if you ask me.

 

That looks complex, you know?

The objective of the dampers is to prevent the springs from oscillating, something that's natural for them to do. While springs create force due to being compressed, dampers create force due to being moved. The faster they are moved, the more force they create.

Now, time to clean up some terminology:

• Bump is Compression, is the damper's rate when the suspension is compressing.
• Rebound is Extension, the damper's rate when the suspension is extending.
• Slow refers to the speed of the suspension, not the car. Slow Speed Damping occurs when the suspension moves "slowly". The suspension velocity can be seen in the Telemetry data. Slow Suspension movement is any movement slower than 65 mm/s, which encompasses most of the suspension movement.
• Fast refers to any suspension movement faster than 65mm/s, which is usually only reached when a kerb is hit very hard.

OK, if we analyze what each damper movement does, we can see what we can influence by adjusting each damper rate. To make this quick:

• Front Bump and Rear Rebound affect corner entry behavior.
• Rear Bump and Front Rebound affect corner exit behavior.
• All of them affect grip on bumpy surfaces.
• Both Slow and Fast damping affect behavior over bumps and kerbs, Slow having a big influence. Yes, most setup guides say the opposite, Slow damping just has too much influence in this set of physics.

To tune dampers, you have to think about them as temporary springs. They will add extra stiffness to the suspension when it is moving, how much depends on the rate. So, stiffening the Front Bump rate would be like adding Spring Stiffness, but only when the Front is compressing, like during braking and cornering. Softening the Rear Bump rate would be like removing Spring Stiffness, but only when the Rear is compressing, like during acceleration and cornering. Similar to springs, we generally want stiffer front dampers compared to rear dampers, that way the front helps stabilizing the rear.

Now, all that talk above refers to Mechanical Grip. We also want to focus on Aerodynamic Grip. That's where the 3rd damper comes into play.

• On the Front, we would like to have the Stiffest dampers we can find in both Bump and Rebound. In Bump so that it stops the nose from bottoming out, in Rebound so that it keeps the nose down and close to the floor for maximum downforce.
• On the Rear, it is a bit more mixed. We want the Bump to be soft, so that the rear has as much traction as possible. In Rebound we could use a stiff setting to keep the rear low, close to the ground and potentially at the highest downforce ride height.

Finally, the rates of the Dampers should also be based on the track you'll be driving at.

• Bumpier tracks favor higher (Yes, higher) damper stiffness, mostly in bump. That allows the suspension to suppress the bumps without allowing the car to bottom out. Do be aware that the car won't behave ideally over bumps.
  
• Smooth tracks favor lower damper stiffness. This increases mechanical grip and allows the suspension to absorb the bumps without significantly moving the chassis laterally. Vertical movement still occurs, so the car might bottom out, something no that worrying in a smooth track.

Summary

• So, Dampers. They are a way to fine tune the car's behavior when the suspension is moving.
• To adjust them, remember the way springs work and apply them here. Bump affect the suspension on compression, Rebound under extension. 
• 3rd Dampers are better used controlling the car's ride height changes, while the Corner Dampers are used to adjust mechanical grip.
• I can't give a single setting in case you are in doubt, the best I can do is a table of damping ratios:

Standard Rates

 Soft/Smooth Track Rates

 Stiff/Bumpy Track Rates

Anti Roll Bars

The final component of the suspension has no effect on the car's ride height, but it still affects our aerodynamics.

For once, we have a single setting for the front and rear instead of three per end. The Springs affect suspension in all modes (Roll, Pitch and Heave), the 3rd Springs only in two (Pitch and Heave). Naturally, we'd like to have a piece of equipment that controls the suspension in the remaining mode, Roll. That's what Anti Roll Bars do.

If we simply used the springs to control the car, there would be excessive body roll. This is a visual effect, however. The true issue is that if we set the springs to control the car's ride height and over bumps, the car would have very, very slow response. This is because the springs would be too slow transferring load, because they are too soft. And if we stiffen up the suspension, ride height wouldn't be ideal, neither would grip or behavior over irregular surfaces.

Instead of compromising, we use a "Spring" that only affects the car in roll. The Anti Roll Bars. Adjusting them is fairly simple, you treat them as springs, but they only affect cornering behavior. So, stiffening the front ARB would be like stiffening the front springs, but without the side effects in regards to bumps and rough surfaces ... generally speaking. Just like the springs themselves, softer means more grip most of them time, though you want some stiffness to get the car turned in and rotated.

Just a little note on how ARBs work, they will reduce the suspension roll. But to do that, it will transfer load from the inside tire to the outside tire. As we know, the more unbalanced an end is, the less grip it will have, Tire Load Sensitivity doing its thing once again. So if we stiffen the front ARB, roll will be lower, but loads will be more unbalanced and grip will diminish as a result.

Once again, anything suspension related will affect mechanical grip, as well as aerodynamic grip. Aerodynamic devices are designed to work when going straight ahead or at slight angles of yaw (As in a car cornering), with no kind of roll into it. You can see the issue. Softer ARB will give a lot of mechanical grip, but aerodynamic grip will suffer. The front wing will roll and downforce will drop. Similarly, the diffuser will roll and downforce will drop.

For this reason, on high downforce cars, increasing the Anti Roll Bars might increase grip, mostly high speed grip. They will stabilize the aerodynamic devices, which will let them produce more grip. For these reasons, doing something fairly crazy like adding rear ARB to increase grip can work, as long as what you want is more high speed grip. The diffuser will be more flat, it will produce more downforce, hence more grip.

To adjust them, you want to start a bit stiff, then soften up the end that lacks grip. If grip under throttle is a concern, soften the rear bar. If the front end struggles to turn, soften the front bar.

Summary

• The last piece of suspension equipment, Anti Roll Bars are useful to quickly adjust the handling characteristics of the car, both in terms of mechanical grip and aerodynamic grip.
• A softer ARB will act as a softer set of springs on everything cornering. It will increase mechanical grip, but will slow the response of that end as well as sacrificing aerodynamic grip.
• A stiffer ARB will stabilize the end's roll attitude. It will increase aerodynamic grip and make the end more responsive, but the cost is mechanical grip.
• If in doubt, set the front ARB at 150 N/mm, the rear at 50 N/mm, and adjust the end that has less grip first.

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