The Art of Setup Building, Part 6: Monster Trucking Kerbs

Ride Heights, Diffuser and Rake

In a low downforce race car, like Touring Cars, adjusting ride height is a balance of setting the car low enough to increase stability and grip (Due to reasons described later), and keeping it high enough to prevent the car scrapping the surface or hitting kerbs. Ride Heights are very useful to adjust mechanical grip, and we will tackle that aspect right away:

Ride Heights: The Mechanical Side

Ride height is the distance between a specific point in the chassis and the ground. In the case of our F1 cars, ride height is measured at the floor of the car. Front ride height is the front points of the floor, rear ride height is measured at the rear points, directly lined up with the rear axle. 

Since our focus right now is the mechanical aspect, we will talk about that. In simple terms that I will explain in the future, a lower ride height will increase overall grip and stability of the car. While this generally sounds good, it stops being good when the car starts touching the ground or even dragging the floor on the ground. F1 cars are equipped with a plank that, if worn too much, will result in disqualification. Fortunately we don't have worry about that, but dragging the floor is extra drag. We want to minimize drag, so we want to find a way to lower ride heights without hitting the ground. Not only that, but lowering ride height limits suspension travel. If the suspension doesn't have enough travel, the tires won't be able to provide grip correctly. The way to respond to that is making the suspension stiffer, which results in less chassis movement, but also could reduce grip for reasons described in the next post.

So now we know that lower ride height is better for grip. However, at times low ride heights could result in the cars bumping on a kerb or bump on the track, or just simply running out of suspension travel through some sections of the track. In those cases, we have no other option, we must increase the ride height, to allow the chassis to clear the bump/kerb. A higher ride height also allows us to use a softer suspension, which will increase grip when used correctly.

There's another factor to consider, but that one is outside of our control. Adjusting the ride height can have an effect on our camber angles. While generally there's no need to change them, cornering behavior could feel a bit different with lower ride heights.

Generally, for the sake of mechanical grip, you want the lowest possible ride heights, with the softest possible suspension, as that allows for maximum mechanical grip around corners.

There is, however, a problem when using ride heights for F1 and other high downforce cars.

Ride Heights affect aerodynamics so much, that mechanical grip is irrelevant.

The True Power of Ride Heights: Maximizing Aero

Let's look at some images.

Pictured: A Jaguar R2 touching the ground down the Monza back straight

I know what you are thinking.

Why is the car generating sparks? I don't have them.     That's a game file tweak that might or might not affect online play. I will mention the variable to alter to get them in a future post.

I still know what you are thinking.

I don't think that looks fine. You shouldn't be hitting the ground.

It is fine to think that. Let's look at another picture.

Pictured: Earlier in the lap, the same R2 was seen absolutely mounting the Roggia Chicane kerbs. From the audio and video, it was noticeably scraping on the kerbs.

Now, I'll be honest. The images are a bit exaggerated. I'm using a PLR variable that increases the physics engine rate from Half Rate to Full Rate. This results in more realistic physics compared to the base game, which also results in the ride heights being lower and bottoming being more common. I'll mention how to enable F1C Hard Mode, aka Full Rate physics, in a future post.

Here's a question. As you can see, the car is noticeably hitting the ground and kerbs around the lap. Should we increase the ride height to prevent that happening?

The correct answer is: Usually, NO

There are two reasons for this, one more relevant to us than the other. The first one ...

Pictured: 2006, en route to an unexpected pole position, Kimi Raikkonen casually monster trucks over the kerbs. He would spend a few milliseconds with all wheels off the ground before proceeding. This was not the first time he did this on a qualifying lap, nor it would be the last.

The advantages of running lower ride heights, specially at a low downforce track like Monza, is just too valuable to just increase them for the sake of riding kerbs, to the point real teams do it themselves. This can change depending on the race track (Imola).

The second reason is the reason why the number 1 exists: Downforce generation is ride height sensitive. Setting the correct ride height will result in maximum downforce for minimal drag. Let's dive into why this is.

Front Ride Height: Maximizing Front Downforce

Last post, I mentioned that the Front Wing was the wing that was most complicated to adjust. Here's the reason why, the Front Wing does not depend just on its own setting. Allow me to present you a graph. This graph shows the downforce of the front wing as a function of the car's front ride height. Data comes from the R2's HDV file.

The red dot is the downforce level we had at Monza, at 290KMH, on the base setup, just like in the infographic of the last post. Ride height was at 35mm off of the ground The green dot is the downforce level if we were to lower the front wing to 10mm. The difference between both is 200N, the green dot being higher. To put that into perspective, if we wanted to increase the base setup's downforce only through the front wing setting, we would have to add 4 clicks of front wing, with the drag penalty associated with it. Or, we could lower the front ride height, get the extra downforce for no change in drag. Not only that, but rear downforce would increase as well, more on that in a moment.

On high downforce cars, the objective is simple. Get the nose down, and keep it as low as possible at all times. You make the front suspension as stiff as you need to, but the nose must be down and stay down. There are a few exceptions, on some tracks a slightly higher ride height increase mechanical grip without sacrificing aerodynamic grip. These are usually slow tracks, and are far and few in between.

Summary

• While the front ride height has an effect on the ability to drive over rough surfaces, as well as mechanical grip, its main duty is to remain low and stable to increase the downforce generated by the front wing.
• Higher front ride height will make it easier to ride kerbs and will make he car more stable over bumps. However, front downforce will be negatively affected. In fact, as we will see in a few moments, overall downforce will be reduced with more ride height.
• Lower front ride height will increase front wing downforce, as well as overall downforce. The sacrifice is a reduction in stability over kerbs, bumps and occasional mechanical grip issues.
• If in doubt, minimize the setting. The downforce benefits beat the stability concerns.

Ride Height and the Diffuser

You are now probably expecting me to say that the Rear Ride Height affects how much downforce the Rear Wing produces. It does not. The Rear Wing is affected by its setting and only its setting. But what is affected by Rear Ride Height is the Rear Diffuser. And it is about time we talk about one of the reasons you want to get those ride heights right: The Diffuser produces a significant amount of downforce, with no drag penalty at all.

Now, this is only partially true, since the body itself produces drag based on ride heights, but maximizing downforce for minimal drag is the objective here. However, the diffuser doesn't work like the front wing where lower is better. For the diffuser, there's a certain, very specific ride height at which is produces maximum downforce. Time for another graph.

This is the same Monza setup, with the car going at 290KMH and front ride height locked at 35mm. The red dot is our current rear ride height down the straights. The yellow dot is the ride height we could have while cornering, and the green is the ideal diffuser ride height of 27mm ... and some change, just remember it at 27mm. This ideal ride height moves depending on mods, but for all base game car content it will be 27mm.

As you can see, we can lose downforce if we go too low, and we can lose downforce if we go too high. We want to keep the downforce as close as possible to 27mm ... when it matters. Now, diffuser downforce isn't really relevant down the straights, we worry more about drag and wings than diffuser ride height (though ride heights are still relevant). However, if we manage to hit the ideal ride height when making corners, specially high speed corners, we will get extra downforce, which means extra cornering speed. That extra downforce can be worth as much as 6 rear wing points, without the drag penalty that would apply.

There's another factor to consider in terms of tuning the diffuser, it is also Front Ride Height Sensitive:

No, I will not be making a 3D Graph or something crazy like that.

Here, same situation, Monza spec, 290KMH, Rear Ride Height is locked at 27mm, Front Ride Height is variable. Red dot is the downforce we got with the default setup, Green is the downforce the diffuser would output at 10mm, about 300N more. Which is, roughly, 5 extra points of rear wing without a drag penalty.

Basically, if you set the ride heights correctly, you will get 10 or more extra points of Rear Wing Angle basically for free, with no increase in drag. Since rear downforce is higher, now the Rear Wing can be reduced, for even less drag, or the Front Wing can be increased for more rotation. The options are open, but not tweaking ride heights is just giving away free downforce for free.

Summary

• The diffuser, while a bit complicated to setup, is a way to get cheap downforce for minimal drag loss. This relies on setting the ride heights, and by extension the whole suspension system, correctly.
• When we talk about ride heights, higher Rear Ride Heights lead to an easier ride over kerbs, bumps, but will reduce rear cornering mechanical grip. The advantages depend, as it will change when the car hits the ideal ride height point for the diffuser, usually changing biasing it to higher speed corners and straights
• Lower Rear Ride Heights will increase rear mechnical grip on cornering, but might result in the car hitting kerbs, bumps or bottoming and dragging the floor down the straights on extreme scenarios. The aero advantages depend, as it will change the ideal ride height point for the diffuser, usually biasing it to low speed corners.
• Front Ride Height also has an effect on diffuser downforce. Lower will increase the diffuser's efficiency considerably.
• If in doubt, lower the rear ride height to its minimal setting, then increase it by 10mm/1.0cm. That should allow enough clearance for the diffuser to work effectively while minimizing ride heights.

Body Drag: Rake, and why we must control it in F1C

So, we've come to the conclusion that lower is usually better for mechanical grip, lower is mostly better for aerodynamic grip but higher works occasionally. We already know about the 3 most important parts of the car, now we must learn about the 4th one. The Body.

The Body itself produces downforce. This is non adjustable and based on the car's design, AKA what the modder elected to do. The Body will also produce drag, and this we can adjust. 

Something else to worry about, eh?

So, there are 3 aspects that alter the Body's drag. The first is the Body's design itself, which alters the base level of drag it produces. This is non adjustable, poorly designed bodies will remain poorly designed no matter what we do, we must work somewhere else.

The second aspect is the Body's ride height over the ground. While the least harmful of the three, it still must be taken into account. Simple, the higher the chassis is off the ground, the more drag it will produce. So, in a vaccum, a car that sits lower to the ground will have less drag and will go faster. Simple until now I think.

The third aspect is the Body Rake, and this one is more significant than the ride height itself. Rake, as you know or are about to know, is the difference between Rear Ride Height and Front Ride Height. Positive Rake is Rear higher than the Front and is the standard setting for F1 cars and ... literally anything that runs downforce. For the reasons explained earlier (Lower Front = More overall downforce, just high enough Rear = More downforce), we want Positive Rake. 

Negative Rake is the opposite, Front higher than the Rear. In real life, you don't want Negative Rake. Mark Webber found out why not, most high downforce race cars turn into wings the moment they hit Negative Rake. Fortunately in F1C, Negative Rake doesn't produce such catastrophic results, but you do lose the advantages earlier explained.

As we found, minimal Front Ride Height and 27mm Rear Ride Height are the ideal ride heights for downforce. This would mean that a 27mm Rake would be ideal, but F1C doesn't work that way. It doesn't care about the Rake value itself in terms of downforce. It DOES care about it in terms of Drag, however.

Simply put, if the rake is at exactly 0, we have minimal drag for the body. So the objective of the setup is to minimize rake and ride heights, right?

If you've been paying attention, you can see the issue. Downforce favors a specific ride height, with lots of rake. Drag favors a different specific ride height, with minimal height and rake. What do we prioritize, downforce or drag? The answer is both. Or rather: Prioritize both when they matter.

If we tweak the setup correctly, we will maximize downforce when we go around corners, while minimizing ride heights and rake down the straights for minimal drag. To do this, we can't just tweak ride heights. We will need some assistance for this to work: We must adjust the suspension system to achieve both objectives.

Summary

• The Body will produce drag at all times. This we can't escape, but we can tweak.
• Generally, lower ride heights will reduce overall drag levels.
• During the setup process, we want to minimize rake, as that reduces overall drag levels.
• Rake influences drag levels more than ride heights. It is better to run with the car a bit higher off the ground just to minimize rake.
• The overall objective is to maximize downforce on the corners, while minimizing drag on the straights. For that, the suspension system must be optimized.

Why all of this works?

Now, I'm no Adrian Newey. I'm not totally sure of how downforce devices work, at least not enough to explain it to someone else in a way I'm sure they'll understand me. So, instead, I'll explain something else.

Ride Height and Weight Transfer

Remember back when I talked about Weight Distribution and Tire Load Sensitivity? That becomes relevant once again. When we corner, weight (Well, load is the proper term) will transfer from the inside side to the outside side. While initially you might think that's good, if you remember the Load Sensitivity talk, you know that a tire that has more load doesn't produce as much grip as you would expect. You then realize there's some loss of potential grip out there due to the load transfer. In an ideal world, we want both tires at both ends to have the same load at all times, that's the moment we get maximum grip from that end. That's some fantasy land magic, however.

Ideally, we want to reduce this transfer. You look at the car, and you see that it has some level of body roll, and think that logically less roll means less weight transfer, and that we should stiffen up the suspension to reduce transfer. Congrats, you have accidentally looked at it the wrong way.

I will add more details in the suspension system post, but for now just know that Body Roll is a function of Weight Transfer and Suspension Stiffness. Weight Transfer is completely independent of Roll and Stiffness. We can have a super soft car and a car with bricks for a suspension, and they both would have the same level of Weight Transfer. You don't have to believe me on this one, you can believe Physics Lord Niels Heusinkveld, though.

Ok, so Suspension Stiffness won't do. What will do, what will affect Weight Transfer is Ride Heights.

Weight Transfer can be calculated, but I that isn't necessary here. However, what I can tell you is that Weight Transfer is a function of Center of Mass height, and Acceleration of the Center of Mass.

(Center of Mass is also called Center of Gravity, and is the point of the car where all forces over the car concentrate on. I call it CoM becuase we call it like that in engineering ... you'll get a bunch of weird looks by calling it Center of Gravity)

Now, if we want less Weight Transfer we either reduce CoM Acceleration or we reduce CoM Height. We can't do the first, to lower CoM Acceleration we would have to reduce our cornering speed, and that's exactly what we don't want or need. So our only option is to reduce the CoM Height. Which is something simple to do, you just drop the ride heights, right?

Well, yes. That's another reason we run lower Ride Heights, less Ride Height means less Weight Transfer, which results in more grip, always the result.

That said, remember that F1 Ride Heights are measured in Milimeters. a small reduction in Ride Heights won't radically alter Weight Transfer. If you are talking GT or low downforce race cars, Ride Height in the name of mechanical grip becomes more relevant.

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