Changing weight distribution will obviously alter CG longitudinal location, and that might have undesirable effects on many other aspects of the car. For this analysis, only the rear axle was considered. Use a 1/4 to one scale. Bear in mind that lateral load transfer affects the balance through tyre load sensitivity (the tendency of the tyres to generate higher lateral forces at a decreasing rate with higher vertical loads). A reference steer angle, which is the average of steer angles of both wheels on the axle, is specified (but the individual slip angles are used when entering the data). Weight transfer of sprung mass through suspension links, The second term is the weight transfer of the body through the suspension links, Weight transfer of sprung mass through springs, dampers, anti-roll bars. In general, it is almost safe to say that the Indycar weighs less than a Formula 1 car. The rear wheels don't steer, or don't steer as . The third term is usually split between springs, dampers and anti-roll bar, and determines the nature of body control and the level of body roll. Lateral load transfer in one axle will change with the proportion of the roll stiffnesses on that axle, not the roll stiffnesses themselves. This seems good, as more weight transfer would appear to be the goal, but less resistance is not the best way to make use of this weight transfer. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each. When you increase roll centre height in one axle you increase the overall lateral load transfer on that axle, while decreasing it on the opposite axle. The input data were based on the manuals from the manufacturer of an important formula category. Applying the small angle assumption, we have: Substituting the definition of the roll resistance moment in the equation above, we have: Solving for and dividing by we obtain the roll sensitivity to lateral acceleration of the car, i.e. . But these forces are acting at ground level, not at the level of the CG. C. Despite increasing the steering angle, the car has taken a line which is not tight enough to take the turn. Lateral load transfer or lateral weight transfer, is the amount of change on the vertical loads of the tyres due to the lateral acceleration imposed on the centre of gravity (CG) of the car. Antiroll bars are generally added to the car to make it stiffer in roll without altering the ride characteristics. All these mechanisms generate a moment about the car that will translate into a vertical load difference between the inside and the outside tyres. The total lateral load transfer on the car can be calculated from its free body diagram, as shown in figure 1. The weight transfer setup recognizes the importance of ride height and roll stiffness in determining a good balanced set up for the car. This bias to one pair of tires doing more "work" than the other pair results in a net loss of total available traction. Deceleration moves the center of gravity toward the front of the vehicle, taking weight out of the rear tires. This can be done in multiple ways. is the longitudinal acceleration, The forces upon the springs are reacted by the tyres, and that contributes to lateral load transfer. When you apply the brakes, you cause the tires to push forward against the ground, and the ground pushes back. We wont consider subtleties such as suspension and tire deflection yet. If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. Transient lateral load transfer is an important aspect of vehicle setup, but lets leave the discussion on that for another day. . It applies for all cars, especially racing, sports and high performance road cars. We now have roll moment arm and roll stiffnesses to play with. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. A quick look at the lateral load transfer equation might lead you to think that lateral load transfer will increase with increasing roll centre heights because of the direct relation in the equation. The roll stiffness of the car is the sum of roll stiffnesses of front and rear axles: One important thing to notice is that the chassis is assumed a rigid body, and hence, the roll angle is the same for front and rear suspensions. 2. draw the ground line ,vehicle center line and center of the left and right tire contact patches. It is easy to modify through the components and is where engineers usually make more adjustments specially between sessions or before the race. Understanding weight transfer is a fundamental skill that racecar drivers need to know. Usually, I'll have 50-80 lbs," Bloomquist told RacingNews.co from Lucas Oil Speedway a few weeks back. A car weighs so much overall, and that is distributed - let's assume for the sake of argument, equally - between front and rear. Then, most of the solutions available will be related to the subject of this post: lateral load transfer. The CG is the middle, then you split 50/50; the CG is more toward one side than the other, then more weight transfer goes on that side and less on the other. This component is the easier to control. The equation for this component can then be expanded: Because the force coupling nature of roll centres is not as widely known as the definition of the term roll centre itself, some people are unaware of this component. This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. This will have a net effect of decreasing the lateral force generated by an axle when the load transfer on it increases. Roll stiffness can be altered by either changing ride stiffness of the suspension (vertical stiffness) or by changing the stiffness of the antiroll bars. They push backwards on the tires, which push on the wheels, which push on the suspension parts, which push on the rest of the car, slowing it down. g Figure 7 shows the gearbox from Mercedes W05, 2014 Formula One champion. If you hold rear roll rate distribution constant at 54 % and increase roll centre height, lateral load transfer will have no significant change. The braking forces create a rotating tendency, or torque, about the CG. The reason I'm asking you is because you're one of the bigger guys in the pit area. During acceleration or braking, you change the longitudinal velocity of the car, which causes load to be transferred from the front to the rear (in . If you have acceleration figures in gees, say from a G-analyst or other device, just multiply them by the weight of the car to get acceleration forces (Newtons second law!). Lowering the CoM towards the ground is one method of reducing load transfer. The car has turned in towards the apex. When it comes to the chassis ride height, that part of the calculation is already baked into the car, and the racer should not look to the 4-link as a way to adjust this. Learning to optimize weight transfer allows us to optimize the grip of the racecar. We derived the equations of lateral load transfer in one axle of the car, showing that its composed of three components: Unsprung weight component not useful as a setup tool because of the effect that it has on ride, specifically wheel hop mode. For example, if you investigate what would happen to the weight transfer in both axles if you held rear roll centre height constant at 30 mm while increasing the front roll centre height, you would see opposite effects happening on front and rear tracks (weight transfer would decrease in the rear axle while increasing in the front). The front end will move faster and farther because less force is required to initially extend the spring. This basically rules out weight distribution as a way of controlling roll angle component. Steering. Figure 12 shows a finite element stress analysis, with colours closer to yellow and green indicating higher stresses. Notice the smaller cornering potential for higher values of the lateral load transfer parameter. Acceleration weight transfer from front to rear wheels In the acceleration process, the rearward shifting of the car mass also "Lifts" weight off the front wheels an equal amount. Conversely, a supercar is built to approximate race geometry with few concessions to prevent spilling the drinks. For context, we are experimenting with carbon-carbon brake discs on a non-downforce car. Since the car does not actually go up on its nose (we hope), some other forces must be counteracting that tendency, by Newtons first law. The analysis procedure is as follows: The potential diagram is a benchmarking of the performance that can be achieved by a pair of tyres. In other words, it is the amount by which vertical load is increased on the outer tyres and reduced from the inner tyres when the car is cornering. Deceleration. The stiffnesses are shown in kgfm/degree, that have clearer meaning, but the data were input in Nm/rad. "Right now, none. Consider the front and rear braking forces, Bf and Br, in the diagram. 1. t In order words, the goal would be to reduce lateral load transfer in the rear axle in comparison to the front axle. Hence: This is the total lateral load transfer on the car. Where is the roll angle caused by the suspension compliances and K is the suspension roll stiffness. Now do the same, but picking a front roll centre height and imagining a vertical line instead. Weight transfer (better called "load transfer") is not a technique, it's a natural phenomenon due to the existence of inertia, that happens whenever you try to change the state of motion of the car. This graph is called the, The actual load transfer depends on the track width and the rolling moment produced by the lateral acceleration acting on the fictitious CG height. Also, the only direct link between the front and rear tracks is the chassis (all-wheel drive cars are an exception), and vehicle behaviour can be evaluated by looking at the relative performance of front and rear tracks. Figure 6 shows the CAD design of a similar gearbox, highlighting the different options for installing pickup points. You already know from steady-state pair analysis and from the discussion on tyre load sensitivity that lateral load transfer will decrease the lateral force capability of the axle. These effects are good for tightening up the car when winged down, but opposite for roll right. Talking "weight transfer" with respect to race driving is . The weight shift component for a single axle will be: Substituting roll angle on the expression above, we have: The total moment from roll angle on a single axle will then be: The lateral load transfer from this moment is obtained by dividing this by the axle track width, t: The three components of lateral load transfer should be added in order to obtain the total lateral load transfer on an axle: The expression above can be utilized to calculate the load transfer on each axle, which can then be used to improve handling. Naturally, you're more inclined to wheelstand with an increase in acceleration. o W usually, production based race cars will not have any front bar at all, and rely stricly on proper spring rates . Figure 14 can lead us to very interesting conclusions. Also, if you liked this post, please share it on Twitter or Facebook, and among your friends. Figure 1 . The equations for a car doing a combination of braking and cornering, as in a trail braking maneuver, are much more complicated and require some mathematical tricks to derive. This makes changes in roll moment arm to control roll angle component useless. In order to determine the crossweight, calculate the sum of the right front and left rear weights, then divide this number by the total weight of the car. The driver is said to manage or control the weight transfer. r The effects of weight transfer are proportional to the height of the CG off the ground. {\displaystyle w} Under application of a lateral force at the tire contact patch, reacting forces are transmitted from the body to the suspension, the suspension geometry determines the angle and direction of these action lines and where they intersect is defined as the roll center. Bear in mind that these values were obtained for a fairly heavy race car with an unreasonably high CG, and this is only one of three weight transfer components.