what is weight transfer in a race car?

You might not be convinced of the insignificance of this term by arguing that those values were obtained for a very light car with a very low CG. B. Weight transfer involves the actual (relatively small) movement of the vehicle CoM relative to the wheel axes due to displacement of the chassis as the suspension complies, or of cargo or liquids within the vehicle, which results in a redistribution of the total vehicle load between the individual tires. Roll stiffness can be altered by either changing ride stiffness of the suspension (vertical stiffness) or by changing the stiffness of the antiroll bars. These data were obtained for the same open wheel car analysed in figure 9, but this time front and rear roll centres heights were held constant and equal, while roll stiffnesses varied. The front end will move faster and farther because less force is required to initially extend the spring. 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 is reacted by the roll stiffness (or roll rate), , of the car. Consider the front and rear braking forces, Bf and Br, in the diagram. If we define , the rear roll rate distribution and , the sprung weight distribution on the rear axle, then the lateral load transfer equation for that axle can be rewritten to give: First, lets analyse what happens when we hold roll rate distribution equal to the weight distribution on that axle. Tire Offsets. To obtain these, I created a MATLAB routine to calculate the total lateral weight transfer from our previous discussion, keeping the front and rear roll stiffnesses equal and constant while varying front and rear roll centre heights. 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). The moment can be divided by the axle track to yield a lateral load transfer component: Where is the unsprung weight on the track being analysed. If (lateral) load transfer reaches the tire loading on one end of a vehicle, the inside wheel on that end will lift, causing a change in handling characteristic. The major forces that accelerate a vehicle occur at the tires' contact patches. On limit conditions, this will translate in one of the axles breaking loose and skidding before the other. For the SI system, the weights should be in N, the angular stiffnesses in Nm/rad, the lengths in m, and the acceleration is nondimensional (because we are dividing lateral acceleration by the acceleration of gravity). The lighter 250-lb/in rate benefits a drag car in two ways. The tires and chassis will also make a difference in the spring selection. So a ride height adjustment to your race car, or a roll centre geometry . This means the driver should be in the car, all fluids topped up, and the fuel load should be such that the car makes your minimum weight rule at the designated time-usually after a race. If changes to lateral load transfer have not significant effects on the balance of the car, this might be an indication that the tyres are lightly loaded, and load sensitivity is small. Lets now see how these components affect each other and how they affect load transfer together. By analysing Figure 9 you can see that lateral load transfer is very sensitive to changes in roll centre height. Car Setup Science #3 - Load Transfer - Paradigm Shift Driver Development In a single axle, the roll resistance moment will be the roll angle multiplied by the roll stiffness of the axle analysed, . During cornering a lateral acceleration by the tire contact patch is created. m 2. The only forces that can counteract that tendency are the lift forces, and the only way they can do so is for Lf to become greater than Lr. The loads in each wheel determine the vehicles maximum cornering, braking and acceleration capability, then the lateral weight transfer is a key factor in a racing car performance. Do you see how small it is compared to the roll stiffness of the car? Before I explain this, let me talk about a good thing to understand the subject the steady-state analysis of a pair of tyres. However, these approaches are limited, ride height being affected by the possibility of bottoming out and track width by regulations that place a cap on vehicle width. These are fundamental laws that apply to all large things in the universe, such as cars. Assuming a 120" wb, 100lbs added 5' behind the rear axle will add 150lbs to the rear axle's scale weight, and take 50lbs off of the front axle. This basically rules out weight distribution as a way of controlling roll angle component. Cornering - Lateral load transfer theRACINGLINE.net Most people remember Newtons laws from school physics. Racing Skills In 60 Seconds - Weight Transfer | Blayze If you accelerate, brake or corner harder, you transfer more weight. g Weight transfer is the most basic foundation of vehicle dynamics, yet holds many of the keys to ultimate car control. 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. Front roll stiffness distribution only modifies Term 3 and hence increasing front roll stiffness always increases understeer. The inputs are essentially the loads and orientations of the tyres, and the outputs are given per unit weight on the axle, allowing for a vehicle-independent analysis. 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. 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!). The next topic that comes to mind is the physics of tire adhesion, which explains how weight transfer can lead to understeer and over-steer conditions. An additional curve might be obtained by plotting the intersections of the lateral accelerations with the lateral load transfer parameter lines, against the reference steer angle. Here the pickup points are highlighted for better comprehension. So far, we have discussed the influence of each component in lateral load transfer in isolation. Figure 8 clarifies. Weight Management for Speed - Playland Speedway The manual of the vehicle used here specified a roll stiffness values ranging from 350,000 Nm/rad to 5,600,000 Nm/rad. The front wheels must steer, and possibly also drive. 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. The same thing happens on the left . If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. Note that this component resists only roll angle, and the entire sprung mass is used here, as this is how we obtained the expression for roll angle. Transient lateral load transfer is an important aspect of vehicle setup, but lets leave the discussion on that for another day. This article explains the physics of weight transfer. This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. The car should be at minimum weight, using ballast as needed to make the proper weight. The fact is, by increasing the roll centre height in one axle, you are increasing lateral load transfer from the direct lateral force component, while at the same time you are decreasing lateral load transfer from roll angle component. Put the driver weight in the car, preferably the driver. is the acceleration of gravity, When this happens, the outside spring of the suspension is compressed and the inside spring is extended. For the analysis procedure, one can adapt the load transfer equation obtained above, using , the weight on the track analysed, instead of , and , the height of a fictitious centre of gravity for the track of interest, instead of . The result will be: Now we know that the load transfer caused by a generic moment about a track will be the moment divided by the track width, and we can use that to analyse the effect of each component of load transfer. Autocross to Win (DGs Autocross Secrets) - Weight Transfer 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 analysis begins by taking the moment equilibrium about the roll axis: Where is the roll resistance moment, and is the roll moment. The braking forces are indirectly slowing down the car by pushing at ground level, while the inertia of the car is trying to keep it moving forward as a unit at the CG level. t the kinematic and elastic components. So a ride height adjustment to your race car, or a roll centre geometry change is a very valid tuning device. Most autocrossers and race drivers learn early in their careers the importance of balancing a car. w In this paper, that issue is discussed with a focus on ride rates, roll rates and simple tire data analysis for a Formula SAE race car. Can you see the trend? f The reason I'm asking you is because you're one of the bigger guys in the pit area. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. This component will, however, be altered by changes in other components (e.g. The distribution of dynamic loads can be altered with aerodynamics, with the regulation of wings or the static/dynamic height of the vehicle. Because of this interaction with the springs, this component is also referred as the elastic weight transfer component. If that was the case, you should work on the roll centres heights instead, and then adjust suspension parameters accordingly. Steering. Queens GTO/Viper. The rear wheels don't steer, or don't steer as . 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. Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. Postby BillyShope Wed Aug 22, 2007 5:48 am. Balance of roll damping will further modify the handling during transient part of maneuver. One important thing to notice is that its difficult to change total lateral load transfer by setup. Weight transfer varies depending on what the car is doing. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. Let us expand that analysis by looking at the pair of tyres. Understanding weight transfer is a fundamental skill that racecar drivers need to know. You must learn how different maneuvers . Sprung Weight Transfer: This is the contribution to weight transfer from the sprung mass of the car, which itself is broken into two sub-components: Please, leave a comment below, to let me know what you liked most in this article or what else you would like to know about the subject, or even some criticism or any knowledge you might want to share. If we know a car needs 52.2 percent crossweight to be neutral based on the front-to-rear percentage, then running 49 or 50 percent in a neutral car means the setup is unbalanced. When a car leaves the starting line, acceleration forces create load transfer from the front to the rear. As an example, Interlagos race track, where the Brazilian Grand Prix takes place has a heavy asymmetry, with only four right-hand corners, and ten left-handers. On independent suspension vehicles, roll stiffness is a function of the vertical stiffness of the suspension (ride rate, which includes tyre stiffness) and track width. Your shock absorbers are considered after your ride and roll stiffness have been selected. When the car moves in one of these directions, the car's weight moves in the opposite direction and compresses the suspension in this area. Weight Transfer - Formula 1 Dictionary This could affect wheel hop (the ride mode that characterises oscillation of the unsprung mass between the road surface and the sprung mass) frequency and amplitude, reducing the contact of the tyres with the ground and hence, reducing grip. These numbers are reported in shop manuals and most journalistic reviews of cars. An important attribute of the suspension is the Roll-centre. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. Braking causes Lf to be greater than Lr. Another example would be the effect of ride stiffness on wheel hop frequency. Transition This is the point at which the car 'takes its set'. Then, a series of steer angles in the range of interest is selected. For a 3,500-pound car cornering at 0.99 g, the traction in pounds is 3,465 pounds (3,500 x 0.99 = 3,465). Hence: This is the total lateral load transfer on the car. Varying the gravity term from 800 Nm to 11395 Nm resulted in a difference of only 0.0148 (from 0.5011 to 0.5159) or 2.96 %. The lateral force of the track is the sum of lateral forces obtained from each tyre. Cars will accelerate, brake, corner and transfer weight from left to right, fore to aft. 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 .

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