The Art of Setup Building, Part 3: He's got so much rear end

Weight Distribution and setup philosophy

We pick up right where we left off. We have 30 minutes to go on Free Practice 2. So far, we have a setup that works well, and tires that are adjusted to do their best to provide grip. Originally, I was planning to talk about the brake system in this post, but I realized there's a much more important factor in play out here. We'll talk about what Weight Distribution does, and why we need to set it up right now before messing with any other setting.

Front Bias v Rear Bias

F1 cars are mid engine, rear wheel drive race cars. This means that there's a lot of weight concentrated at the rear of the car, more than at the front. The ultimate goal of the engineer when building a setup is to balance this weight across the 4 tires as effectively as possible. In the ideal universe, all 4 tires would have the exact amount of weight on them at all times. This is only possible in fantasy land. 

The next best solution is get weight distributed as effectively as possible through as many scenarios as possible. There are many ways to do this, like suspension system adjustments or aero adjustments. Or we could outright move weight around. This is what Weight Distribution does. You can move weight to the front or the back, and that alters the behavior of the car. To do that on our car, we go to the Mechanical and Aero menu

Yes, there's a gigantic amount of adjustments here, we'll deal with them in due time. For now, our focus is on the lower part of the screen, the Weight Dist. (F:R). What this setting tells us the percentage of weight on the front tires and the percentage of weight on the rear tires. In this case, we have 42.5% of the car's weight on the front tires, and 57.5% on the rears. This doesn't take into account the weight added by fuel. Let's start adjusting. Clicking left will increase front weight, clicking right will increase rear weight.

Now, I have moved the weight as forward as I can possibly move it. Different chassis will have different weight distribution ranges.

Why would you want more weight to the front? Stability. Once again, I will describe the physics involved later, but moving weight to the front of the car will make the car considerably more stable during cornering. This extra stability allows you to ride kerbs considerably more easily. Weight distribution to the front of the car is ideal for low grip tracks, as the rear won't be trying to kill you entering corners. 

There are two problems with this. The first is that the extra stability is what some of us call Understeer. The car will be less responsive, lacking front grip during turn in and mid corner. The second is that, with the rear less loaded, acceleration will be a bit more complicated. To an extend, braking too. This is why Front Wheel Drive cars behave like they do, weight at the front make the car stable, but they are hard to turn. They understeer.

I completed the run and got a lap time, we will analyze it later.

Here, I moved the weight as rearwards as I can possibly move it. Once again, I went out on track for a few laps to see a lap time.

Why you want weight on the rear? Rotation. A rear weight biased car will be more willing to rotate. The front will stay planted while the rear will want to rotate. This means that it is easier to carry considerably more speed into the corners, as the car will help you take the corner. At high grip tracks, rear weight bias is king, as you don't have to worry about the rear getting too loose, while still enjoying all of the benefits. Traction under acceleration and braking grip are also improved.

The problem? Rotation is known to some as Oversteer. The car will like to swap ends and spin a bit more often if the rest of the setup is scuffed, or if the driver is not ready. A rear weight biased car needs a different kind of technique than a front weight bias car. This is why high performance cars are mid engine, more rotation generally means more performance.

What is best? I don't know.

We can have 2 drivers of equal skill, but different setups in terms of weight distribution, and but more likely than not will post the same lap time, simply because the setup benefits them. This is where we need to talk about something.

Setup philosophy: What do you want and expect?

To properly setup the car, you must have a pretty solid idea of what you want the thing to do.  You want to know what kind of balance you want at high speed and at low speed. You need to know if you prefer understeer, oversteer or neutral steer before we head further into this. If you don't know what you want, you can't make the car work for you.

It doesn't matter if you prefer understeer or oversteer, both can produce the same pace with the correct driver.  They will just gain time in different places. Your driving style isn't wrong unless you can't do things consistently, or if you don't know what it is. That's the reason why setups from another driver might not work for you. What they consider mild understeer could be terminal understeer to you. My neutral steer could be mild oversteer to someone else.

If you have a solid idea about what you want from the car, you'll be able to deal with handling issues in a way that makes the car better for you. If you don't, you'll have to burn time testing so many settings that it isn't worth it.

With so many setup options, you can get the result you want in many different way. I can make a car feel perfect for me using a lot of front aero levels and a mechanical setup biased to understeer. Or I can make a mechanical setup biased to oversteer and lower front aero levels to counter.  I can make it oversteer at all speeds, oversteer at high speeds and understeer at low speeds, the other way around, or understeer everywhere. But to do that, I must have an idea of what I want to achieve and a good base to start my work. And the best way to start with that base is making the car comply to my preferred driving style, then work the rest of the settings around that. The best tool to start with is the weight distribution.

Time comparison

Let's pick back up. I did a stint with the weight fully biased forward and the weight fully biased rearward. I was taking mental notes of how the car felt and how it behaved. Let's look at the telemetry.

The red line is the lap with weight to the front, green line is the line with weight to the rear. And while, yes, the green lap was quicker, there's more to it than that.

With the weight at the front, I struggled to get through turn 1 carrying a decent amount of speed. The exit of Maggots-Becketts was good enough to recover that lost time. Sector 2 was just abysmal, as I couldn't get the car to respond to me the way I wanted it to. Sector 3 was perfectly fine. Through out the lap, I could definitely feel the car being more stable and harder to rotate. I could throw it over kerbs just fine, but it lacked rotation at times. However, I feel that I could hit the reference lap, the lap we made on the last post, with more running and getting used to it.

With the weight at the rear, the car was more willing to turn. T1 was definitely easier, and I could carry a lot more speed, up to 250KMH at the apex. The front weight bias car could only carry speed around the mid 230s. However, exiting Maggots-Becketts was an adventure. S2 felt fine. I made up some lap time around S3 with the extra rotation, but lost it on the exit of the final corner, oversteer annoying me.

Watching this data, you can probably guess that I prefer oversteer to understeer, despite the terrible S2 on the front weight bias lap. You would be correct. I prefer to take a car with natural oversteer and then fine tune it into slight oversteer or neutral steer, depending on the track. I can also work the other way around on special tracks (Imola being one of them), but I will use a natural oversteer car for this track. I felt very comfortable in the maximum rear weight bias car, I will use that as the base for the following adjustments.

All of that was done in about 20 minutes of run time. With 10 minutes of FP2 remaining, we still can tweak another element on this car. That will be done in the next post.

Summary

• From this point onward, you need to put some thought into why you are adjusting the setup. The objective is always to make a car comfortable to you and compatible with your driving style.
• Biasing the weight of the car forward will add stability to the car, at the cost of rotation.
• Biasing the weight of the car rearwards will make the car more willing to rotate, though the effects can be excessive.
• All of the setting range is at your disposal. You can use a central setting, or one of the extremes with no issue.
• Thanks to the absurd amount of settings we have, Weight Distribution won't impact significantly the final lap time. It will, however, affect the direction we take with the setup, as well as the nature of the car.
• If in doubt, leave this setting along. The middle range is good enough, thanks to the variety of settings at our disposal.

Other effects

In the previous posts, I mentioned that you should always keep track of the tire temperatures, as they can inform you of setup issues. It is always a good idea to check them after a significant setup change.

Green line is the rear weight lap, Blue is the front weight lap. I'm comparing lap 5 of each time to make things more fair. At the front, the front weight lap had slightly higher temperatures compared to the rear weight lap. At the rear, the rear weight lap had significantly higher temperatures compared to the front weight lap. Let me explain.

As you know, tires get temperature by getting squished and rolling on the road, and by sliding. If a tire lacks grip, it will inevitably start sliding. That's what's going on here. We already determined that the front weight bias setup is understeery in nature, and we can see that in the temperatures. Focusing on the left side, the highest temperature the rear left tire reaches is 120ºC. The max temp on the front left is 15ºC over that. This tells us that the front tires are sliding more than the rears, a sign of understeer. (Ignore the front right, as we barely have left handers that can heat that up).

The rear weight bias setup is oversteery in nature. The front left, on that setup, peaked at 131ºC. The rear left did so at 130ªC. Now the rears are sliding more. That's a sign of oversteer.

Another factor, generally rear weight bias setups will increase tire temps. This is due to the fact that the car will be more willing to slide sideways very, very slightly. You might not perceive this, but the tires do. They don't like to slide across the surface like that and will heat up. Not just the rears, but also the fronts, though not to the rate of the rears by any stretch of the imagination. The front weight bias setup limits the sliding to the front tires, which means the rears will cool off while the fronts heat up considerably more.

Weight distribution is quite powerful in terms of moving temperatures around, although I wouldn't use it for that purposes unless temps are terribly unbalanced. Even then, I'd try to think a logical reason for the unbalance. For example, Monaco will destroy the rear tires because they have to accelerate from low speed so often. Silverstone will overheat the left front because most of the track's high speed corners are right handers.

Why all of this works?

Once again, here's the sciency, optional wall of text part that shall explain you why things work like they work instead of the way logic tells us they should work.

For those of you reading, I think you might be wondering ... shouldn't grip increase if I put weight there? Shouldn't a front biased car oversteer and a rear biased car understeer? To answer the first question: Yes, but there is a pair of "buts". To answer the second question ... no, Weight Distribuition works the other way around.

Tires are weird: Load Sensitivity

Let's talk tires again, we'll be talking tires quite a lot in these "Why all of this works?" sections. Tires are what's known as "Load Sensitive". To put it simply, if you duplicate the weight on a tire, the grip it provides does not duplicate. 10 times the weight on a tire is not 10 times the grip. This will become more relevant when we talk suspension and roll, but for now, just know that adding weight to one of the ends of the car will, indeed, add grip. But that extra grip is less than what you think it is, a good chunk of the grip will now be dedicated to dealing with the extra weight on them.

Longitudinal Grip: Acceleration and Braking

Remember when I said there's a pair of "buts"? This is where they come in. Everything I said above? Mostly influences lateral/cornering grip, and is the answer to question 2. In terms of longitudinal/acceleration/braking grip, more weight to an end of the car does exactly what it says on the tin. If you put more weight to the front, the front tires will be able to deal with longitudinal demand, aka braking. They will be less likely to lock up under braking. The problem is that the rear tires now have less grip, so hard acceleration will be much more difficult and are more likely to underrotate/lock under braking. On the other hand, more weight at the rear allows the rear tires to sustain more longitudinal demand. You can accelerate harder and they can sustain more braking force. The sacrifice is that the front tires won't be able handle as much longitudinal load ... braking force.

Reading that, you would imagine you would prefer to have as much weight at the rear since that means you can accelerate harder, and balance the brakes better. While that would be true ... well ... we have the tools to answer question number 2.

Lateral Grip: Cornering, living in Opposite World

As soon as you add cornering force, Load Sensitivity becomes relevant once again. Move weight forward, and while the front tires has extra grip in a vacuum, a lot of this grip is expended dealing with the extra weight. The result is less grip available to develop cornering force. On the other hand, the rears have less grip, but also less weight. More of the remaining grip is now used for cornering force. The result is that the front won't turn as hard, and the rear will stay more planted. Understeer.

Move weight rearwards and the opposite happens. The front tires, while unloaded, can dedicate more of their grip to create cornering force. The rears, while more loaded, also waste some of their grip handling the extra weight over them. This means they can't generate enough cornering force to counter the front force, and the rear will start sliding and rotating. Oversteer.

Summary

• Due to the way tires work, Weight Distribuition works the way common sense says it should, and the opposite way commons says it should.
• In the longitudinal way, that is acceleration and braking, adding weight to one of the ends of the car will directly add grip to that end of the car. More grip under throttle and braking can be found by moving weight around.
• In the lateral way, the notion is flipped. Adding weight to one of the ends of the car will reduce cornerning grip at that end. Adding weight to the front generates understeer, adding weight to the rear generates oversteer.
• As mentioned in the main article, you can use this to adjust the tire temperatures. While not my preferred method, it is a choice and a legitimate way to handle weight distribution.
• If you are still doubting, there are more tools to adjust balance. This is a powerful tool, however. Keep it in mind.