Weight distribution is not the most intuitive concept in car racing. However, it is one of the most important, as it comes into play at almost every stage of a race. It is not a straightforward concept, and there are a lot of parts to it. So, how does weight distribution affect race car performance?
The weight distribution of a car will influence several things such as how quickly the car accelerates and decelerates, and also how well the car handles when cornering. This is because of the weight transfers that occur when the car is moving, affecting levels of tire grip.
Before we go into detail about how it affects the performance of a race car, we must first give a basic explanation of what weight distribution is. Then, we can discuss what this means for you as the driver, and how it can be used to your advantage.
What Is Car Weight Distribution?
Weight distribution describes how the weight of a car is spread out, usually in terms of front vs rear. The weight distribution is usually quoted in terms of percentage at the front vs back. Perfect balance would thus be 50/50, and front weight distribution would be 60/40 and so on.
At rest, or at a constant speed, the weight of the car could be measured by placing a set of scales under each tire. The weight at each corner would most likely be slightly different, and this would describe how the weight is distributed around the car. How this is affected by the movement of the car is called weight transfer, which we will discuss in more detail below.
Weight & Mass
The weight in this case is technically the mass, in that it is what is measured in units such as kilograms, pounds or tons. The way that this mass interacts with gravity is called the weight, but for simple purposes we will just be considering the mass as the weight. This means if you have a 2000lb car with 50/50 weight distribution, 1000lbs would be over the front tires with 1000lbs at the back.
This is a big generalization, and there is a lot more involved. For now, all you need to know is that weight distribution is important and takes into account everything within the car from the engine to the tires themselves, as well as the seats, the chassis and even the driver too.
One important distinction to make is between weight distribution and weight transfer. They both work in conjunction with each other, as the way that the weight shifts when the car moves will obviously be dependent on where that weight starts before the car is moving. Once again, we will go over specific examples below, but let’s first describe some basic features of weight transfer.
Weight vs Load
There are two things to consider here, with one being weight transfer, and the other being load transfer. Strictly speaking weight transfer involves the movement of the center of gravity of the car along with other physical things like the fluids inside, and the way that the vehicle rolls (more on that shortly).
Load transfer is the movement of the weight across the four tires. This is what we will be talking about for the rest of this article, as the weight transfer of the fluids and the roll of the car is very small in comparison to the load transfer. However, for the sake of minimizing confusion, we will be referring to everything from this point on as weight transfer, even if it is actually a mix of both.
So, weight transfer is essentially the movement of the weight of the car across the four tires as the car moves. When the car is at rest, or at constant speed, there is no weight transfer, as for it to move there needs to be an external force acting on the car, such as acceleration or deceleration. The weight will shift in the opposite direction to the car’s movement.
If the car is braking, the weight shifts to the front. This is why when you are driving and you slam on the brakes, it feels like you are coming out of your seat. It is also why you wear a seatbelt, as it prevents you from going through the windshield. Because of this transfer of weight, the front of the car becomes much heavier than the back and is pushed into the ground.
This causes the front suspension to compress, and the car is often said to be “diving”. As the weight at the front pushes the front of the car down, the back is raised slightly, as it is much lighter. This can make the car prone to oversteering if the wheel was to be turned, as the back end of the car has much less grip than the front.
The Effect On Grip
Essentially, as more weight is put over the tires, their level of grip increases. Thus, when you brake, the front tires get a lot of grip, but the back tires have less weight over them and so lose grip. As the car only has a certain amount of grip available, due to the size, shape and weight of the car, as well as the type of tires, it becomes a battle of balance over each tire.
When the car accelerates, the opposite happens, and the weight of the car is shifted to the back. This is why it may feel like you are being pushed into your seat under hard acceleration. This weight shift means there is a lot of grip at the rear tires, but less at the front. This makes the car more prone to go into understeer due to the lack of grip on the turning front tires.
In this case, the rear suspension is compressed, and the car is said to be “squatting”. However, it is not just longitudinal movements that affect weight transfer, as the way the car is moving side to side will cause the weight to shift as well. If you were to turn the wheel to the right at a constant speed, the weight would shift to the left and vice versa.
Turning The Car
In this case, the car is said to be “rolling”, and the weight shift to the outside tires causes an increase of grip at those wheels. The inside tires raise slightly as the inside wheel suspension raises, and this is why you can ride over kerns with your inside wheels when taking a corner, as there is less weight over the inside tires.
Obviously, if you accelerate or decelerate while turning, the weight will shift forwards and left or backwards and right and so on, depending on the combination of movements. However, this can become quite complex, but it should just be noted that the weight will shift in the opposite direction to that in which the car is moving.
We Want A Balance
As we have already said, the car only has a set amount of grip available to use for turning, accelerating and decelerating. We have talked more about this in our traction circle article, but all you need to take away for the moment is that you are trying to balance the weight of the car over the four tires as much as possible, in order to maximize grip at all times.
Minimize Weight Transfer
The more weight transfer there is, the more grip is lost, and the less balanced the remaining grip is across the four wheels. Thus, you want to limit weight transfer as much as possible in order to free up grip. This is achieved by making slow and smooth movements in all directions, with smooth acceleration and braking, and slow turning of the steering wheel.
What You Need To Know
Doing this will help to guide the car in the right direction without tossing the weight around too much, causing a loss of grip. Knowing that the weight distribution will be affected by the movements of the car through weight transfer is essential to be able to control the car, and to know what will and won’t push the car to and beyond its limits of traction.
The Center Of Gravity
We will now discuss some more technical aspects of the idea of weight distribution and weight transfer. The first of these is the center of gravity (COG). The COG is the average location of the weight of the car. This will not always be in the center of the car itself but will be somewhere between the front and rear axles.
Where Is It?
If most of the weight of the car is over the front axle, then the center of gravity will be near the front of the car. If the car is rear-heavy, then the COG will be towards the back of the car. The COG is also affected by lateral weight as well, and so it may be slightly off center to the right or the left, depending on the weight distribution and whether or not the driver is in the car.
The center of gravity is also affected by the vertical weight of the car as well. If the car has a lot of its weight low to the ground, then it will have a lower center of gravity. If the car has a lot of its weight substantially higher than the wheels, it will have a much higher center of gravity. For a race car, the center of gravity should be as low as possible.
High vs Low
The best way to illustrate this is with an example. Take a double decker bus, and image it trying to go around a corner at high speeds, say around 50mph. As you can probably imagine, the bus would tip over as it turned, which is obviously not a good thing and is why you won’t see many buses trying to go round corners at much more than 10 or 15mph.
If you then think of a race car, they might go around the same corner at closer to 100mph without a struggle, and if they do, they will be more likely to spin out rather than roll over. This is why a lower center of gravity is key, as it keeps the car lower to the ground, and this gives it as much grip as possible.
The next concept we will discuss is the idea of slip angles. These are quite difficult to imagine in your head, and so we have provided a diagram below to help make a bit more sense of it. Essentially, these allow you to understand what a tire is going through when the car is turning, and it helps to illustrate the effects of weight transfer too.
The Contact Patch
Tires are made out of rubber, which is an elastic material. Essentially, this means they can move quite a lot when under pressure. The part of the tire that touches the road is called the contact patch, which is a small rectangular patch of rubber that maintains contact with the ground and is the part of the tire that provides the grip to the car.
As the wheel rotates, the actual part of the tire that is considered the contact patch changes, but the size and shape of the contact patch both stay the same as the tire rotates. The patch is very small when compared to the size of the tire, and so the general rule for racing is to maximize the surface area of this contact patch in order to increase the grip of the tire.
Regardless of the size of the contact patch however, there is bound to be the creation of what is known as the slip angle. If you take the middle diagram below as an example, this would be how things would look for a car that is at rest or moving at a constant speed. The direction of the tires is forwards, and there are no external forces acting on the car.
No Slip Angle
This means there is no slip angle. The slip angle is the difference between the direction that the tire is pointed, in this case forwards, and the direction that the tire is rolling. In this case it is not rolling (laterally) and thus there is no slip angle. We touched on rolling above, when talking about how the weight shifts when the car is turning.
The tire rolls to the side when turning due to the forces acting on it, causing the rubber to morph slightly at the contact patch. For the sake of explanation, and to make it easier to see, we have drawn tire treads on the tires below. In the middle diagram, you can see that the tire treads are all pointing forwards, even at the contact patch.
Obviously, the rear wheels are not going to turn (although all wheel steering does turn them slightly, that is not something we are considering here), and thus their direction of travel in all cases is the same – forwards. However, the first and third diagrams illustrate what happens to the tires when the wheel is turned to the left and right respectively.
Starting with the first diagram, where the car is turning left, it can be seen that the front wheels are now pointing to the left. However, the contact patch, shown in the middle of the tire, still has its treads pointing straight ahead. This is because the weight of the car has shifted over to the right-hand side, causing the contact patch to be “pushed” in that direction relative to the car’s movement.
This causes there to be a difference in the direction of the tire movement, and the direction the tires feel they should be moving given the weight and forces acting on the. This difference is called the slip angle, as it is said that the tires are slipping in a different direction to the way that the driver is trying to turn the vehicle.
Front & Back
The same thing happens at the rear tires, and although it is clear that they are pointing forwards, the tires are slipping to the right due to the weight of the car being transferred in that direction. Thus, there is a slip angle to be found at the front tires and at the rear tires as well.
In the third diagram, the car is turning right. The same thing happens, in that the weight is now shifted to the left, causing the tires to slip in that direction relative to the wheel’s direction. The slip angles below are arbitrary, and are only for demonstration purposes, but in the real world they can be used to determine a car’s behavior.
If the car has a larger slip angle at the front than it does at the back, this means the front tires are struggling to point the contact patch in the direction in which the tires are pointing. This suggests there is less grip at the front tires than at the back, and we know that this usually leads to understeer.
This can be explained in turn by the idea of weight distribution. If there is less weight at the front of the car than at the rear, we know that the front tires tend to have less grip, and thus the car is more likely to understeer. The idea of the slip angle just gives us more detail of what is going on at the ground level, and the same can be applied to oversteer.
If we have less weight at the back of the car, we have less grip at the rear tires. This will cause the tires to struggle to point in the right direction, leading to a larger slip angle at the back tires than at the front. This in turn leads to an increased likelihood of the car oversteering, which is what we would expect if the back of the car has less grip.
This does not apply exclusively to the weight distribution of the car, as the way that the weight is transferred will also affect this. If the car is accelerating through a turn, then there will be more weight at the back tires, and less at the front. This will decrease the weight over the front tires, thus increasing the slip angle and increasing the chance of understeer.
Once again, the same process works in reverse for oversteer as well. So, it is important to understand what slip angles are, as they will give you a better understanding of why slamming the brakes while turning is likely to spin the car, and why you want to minimize the slip angles as much as possible to maximize the grip of the car.
Other Things That Affect Grip
Many Other Factors
The weight distribution of the car, and thus the weight transfer of the car, will affect the grip of the tires as we have discussed above. But there are many other factors that will affect the level of grip that the tires experience, and it is worth noting them here in order to paint a full picture of the way that the car maintains its balance of grip through corners and on the straights.
The tires themselves play a key role in managing grip, and this can be affected by the size, width and compound of them. The softer compound tires will offer more grip, and harder tires offer less grip. The wider the tire, the more surface area, and thus the more area there is for the contact patch to grip the ground.
The tires are part of the suspension system in the car, which is what moves under the weight and thus dictates to what extent the weight transfers throughout the car. Other components of the suspension system will work in tandem with the tires, such as anti-roll bars and various rotors and springs, to help minimize weight transfer and maximize grip.
Other things like the track surface and the weather conditions will also obviously have an effect on the levels of grip, but the main factors are the suspension system and the weight distribution. Thus, it should be clear that in order to maximize and maintain grip, a solid understanding of weight distribution and weight transfer is a must.
A Note About The Engine Position
Where Is The Engine?
The weight distribution is affected by where the weight of the car sits, and one of the heaviest components is the engine. You will find there are several different configurations on the market, with one of the most popular putting the engine in the front of the car. You will find both front and rear wheel drive options with this engine position.
By having the weight shifted to the front of the car to begin with, it counteracts the weight shifting to the back when the car accelerates. If the distribution was 60/40 with more weight at the front, when the driver accelerates the weight will shift closer to 50/50, and although it may go beyond that, it will still remain more balanced than if it were to have a 50/50 weight distribution at the start.
Finding A Balance
If the car was to brake intensively however, even more weight would shift to the front, which makes the back even lighter and thus more prone to spinning out. If the engine is located in the back, then this problem flips on its head, and the car will often struggle to gain grip at the front tires when under intense acceleration.
Thus, there is a balance to be found between the drive train, the weight distribution and other things like the brake bias of the car to ensure it is suited for the particular drivers’ style. There are also mid-engine cars, which help to balance the weight distribution further, and thus these are often favorable for race cars for maximum grip and power.
Weight distribution is an important concept in car racing. There are many components to it, and it can affect a lot of different aspects of the driving experience. These include things like braking and accelerating, as well as turning, and the overall handling of the car.
The way that a car’s weight is distributed will be dependent on a lot of different factors, with the main one being the engine position. Weight distribution will have a drastic effect on how the car handles at high speed, and so whether the car is front, rear, four- or all-wheel drive is also important to consider. Careful tuning of the car’s weight distribution and brake bias is key to maximizing performance.