If your driver complies about oversteer in the slowest corners, it means that the front axle is generating higher lateral force than the rear. Now lets stop for a moment to analyse the influence of the gravity term on the lateral load transfer component. For example, imagine a vehicle racing down a straight and hitting the brakes. Balance of roll damping will further modify the handling during transient part of maneuver. 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. By the methods presented here, the simplest solution would be shifting roll rate distribution to the front, by either stiffening the front antiroll bar or softening the rear. Figure 9 shows a contour plot of lateral weight transfer sensitivity (lateral weight transfer divided by lateral acceleration) on both axles of an open wheel single-seater. {\displaystyle h} {\displaystyle w} The secret to answer this question is to focus not on total lateral weight transfer on the car, but instead, on how it is distributed between front and rear tracks. 2. draw the ground line ,vehicle center line and center of the left and right tire contact patches. This leads some to think that increasing roll centre heights will actually decrease weight transfer because it reduces roll. After that, we will see how the components of load transfer can be manipulated to tune the balance of the car. It is what helps us go fast! 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. Understanding the physics of driving not only helps one be a better driver, but increases ones enjoyment of driving as well. Conversely, if you hold roll centre heights at about 254 mm and vary rear roll rate distribution, lateral load distribution wont suffer relevant differences. In conclusion, it was a huge effort by Tin . The term is a gravity component that arises due to the sprung CG being shifted to the side when the chassis rolls. Here the pickup points are highlighted for better comprehension. The first one to analyse is the kinematic or direct lateral force load transfer component. In a dirt race car, our setups determine where the weight that has transferred goes. The initial lurch will sink the car. Figure 10 shows the plot of the roll angle component versus gravity term. Some setup changes might apply, for example, CG might be lowered by reducing ride height, and track width might be increased by changing wheel offsets properly or using wheel hub spacers. Conversely, under braking, weight transfer toward the front of the car can occur. Weight transfer is a function of car weight, CG height, wheelbase, and acceleration. We dont often notice the forces that the ground exerts on objects because they are so ordinary, but they are at the essence of car dynamics. This component of lateral load transfer is the least useful as a setup tool. A lateral force applied on the roll axis will produce no roll; Front and rear roll rates are measured separately; Tyre stiffnesses are included in the roll rates; Vehicle CG and roll centres are located on the centreline of the car; We used steady-state pair analysis to show once again that lateral load transfer in one end of the car decreases the capability of that end to generate lateral force. By simply raising or lowering the couplers, our machines can gain thousands of pounds for traction. G is the force of gravity that pulls the car toward the center of the Earth. The sprung mass used was 675 kg, which gives a weight of 6621.75 N. With a CG height of 254 mm and the minimum roll centres specified in 3 mm, which is very low, the moment arm will be 251 mm. As you begin to turn in (you may or may not still be on the brakes) the weight begins its transfer from inside to outside as the lateral g-loading increases. The tires and chassis will also make a difference in the spring selection. Because of Newtons first law. The following formula calculates the amount of weight transfer: Weight transfer = ( Lateral acceleration x Weight x Height of CG ) / Track width For the trailer, the chain pulls down . MichaelP. The difference in height between the roll center and center of gravity of the sprung mass gives rise to a moment. Then, the total lateral weight transfer is therefore a sum of the three parts: The first term is usually small in comparison, and it is also difficult to modify, and is therefore, sometimes ignored. In a brief feedback after the first outing (a set of laps in a session) of the free practice session, the driver complains about excessive oversteer in these parts of the circuit. m In a single axle, the roll resistance moment will be the roll angle multiplied by the roll stiffness of the axle analysed, . Performance Engineer, withexperience in IMSA LMP2, Porsche Cup Brazil and othercategories. Also, when the chassis rolls, the CG of the sprung mass will be shifted sideward, and that will give rise to another moment that will add to lateral load transfer. The fact that the problem occurs in the slowest bits of the circuit might rule out the possibility of aerodynamic changes as a solution. Why? Acceleration causes the sprung mass to rotate about a geometric axis resulting in relocation of the CoM. 21 Shifting. Weight transfer varies depending on what the car is doing. Some large trucks will roll over before skidding, while passenger vehicles and small trucks usually roll over only when they leave the road. We can split the inertial force into sprung and unsprung components and we will have the following relation: Where is the moment acting upon the sprung mass and is the moment on the unsprung mass. Use a load of fuel for where you you want the car balanced, either at the start of the race, the end of the race or an average between the two. We have established that playing with the unsprung weight component is not the smartest thing to do, so lets focus on the sprung weight components, i.e. 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. What would you do, in order to solve the problem? 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. Now you know why weight transfer happens. It is a fact of Nature, only fully explained by Albert Einstein, that gravitational forces act through the CG of an object, just like inertia. Most people remember Newtons laws from school physics. Designing suspension mounting points- ifin you do not have access to the software I mentioned and you do not yet have the car built, you can pick up the old Number 2 pencil and start drawing. Calculating the load transfer in a vehicle is fairly straightforward. 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. 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. 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. 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. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. For weight transfer to be useful to the driver in controlling the car, the driver would need to feel the weight transfer, or something related to it. This being a pretty typical "clubmans" type car it sits properly between the road going sports car and the sports prototype figures given in the table. In some categories, the rear suspension is mounted on the gearbox, for example, Formula 3, shown in figure 5. The rear wheels don't steer, or don't steer as . If the tyres of the car are lightly loaded, there might not be enough load sensitivity in the tyres, so that even if one end of the car takes all the lateral load transfer, the lateral force performance isnt degraded significantly. The minimum weight of the car to take part in the X275 drag race is 2625 pounds. The reason it is relevant is that the amount of weight on a tire directly affects how much grip is available from that tire. Weight Transfer - A Core of Vehicle Dynamics. When the car corners, lateral acceleration is applied at this CG, generating a centrifugal force. On limit conditions, this will translate in one of the axles breaking loose and skidding before the other. Set tire pressures first. If that solution doesnt work, you could have roll centre heights that would give a roll axis too close to the sprung CG, as discussed before. 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. In order words, the goal would be to reduce lateral load transfer in the rear axle in comparison to the front axle. Referring to the figures, we have illustrated a street car weighing 3000 lbs, and with a typical FWD street car's weight distribution of 60% front and 40% rear. In this figure, the black and white pie plate in the center is the CG. Allen Berg ranks among Canada's top racing personalities. is the total vehicle weight.[7][8]. Lifting off the gas brings the car's momentum forward. D. As long as the tires stay on the car, the ground pushing on them slows the car down. In this analysis, we will be interested in lateral load transfer in a single axle, and I will discuss the three mechanisms by which that happens, namely, roll resistance moment from springs and antiroll bars, direct lateral force load transfer and lateral load transfer from unsprung mass. Figure 8 clarifies. This analysis may even be used to prepare tyre data, in order to make the bicycle model more realistic. This basically rules out weight distribution as a way of controlling roll angle component. 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 weight transfer is caused by rotational forces centered at the hitch ball. Weight transfer is affected by the distance between the CG Height and the roll centre. 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. Load transfer causes the available traction at all four wheels to vary as the car brakes, accelerates, or turns. First off I would point out don't assume your tires are correct just based on there all but the same as the leaders, take a kart with 59 % left and 70 % cross he will be on a more juiced tire than a kart with a more balanced set-up like 56 % left and 57 % cross, now if you know his chassis and set-up 100 % ya you can feel little better about the Tires. As fuel is consumed, not only does the position of the CoM change, but the total weight of the vehicle is also reduced. FROM LAP TIME SIMULATION TO DRIVER-IN-THE-LOOP: A SIMPLE INTRODUCTION TO SIMULATION IN RACING. It is defined as the point at which lateral forces on the body are reacted by the suspension links. You will often hear coaches and drivers say that applying the brakes shifts weight to the front of a car and can induce over-steer. Roll angle component or elastic component the most useful component as a setup tool, since it is the easiest to change when antiroll devices are present. f Bear in mind that the roll moment arm is the perpendicular distance between the CG of the sprung mass and the roll axis. But why does weight shift during these maneuvers? By analysing Figure 9 you can see that lateral load transfer is very sensitive to changes in roll centre height. The weight distribution on the rear axle was 54 %. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. To further expand our analysis, lets put the theory into practice. w Usually, I'll have 50-80 lbs," Bloomquist told RacingNews.co from Lucas Oil Speedway a few weeks back. This characteristic is also observed here. For this analysis, only the rear axle was considered. This is reacted by the roll stiffness (or roll rate), , of the car. Reference:Dr. Brian Beckman The Physics of Racing, Michelin Raceway Road Atlanta is 2.54 miles long, with 12 turns winding their way through the scenic Georgia countryside. Substituting the values on the terms inside the brackets, we have: But if we assume that front and rear roll centers have the same height, then the moment arm will be given by: Substituting into the weight transfer equation yields: This shows that when weight distribution and roll rate distribution are equal, for a horizontal roll axis, the sprung weight load transfer component will be independent of roll centres heights. This is given by: Here, is the sprung weight distribution to the axle being analysed and is the roll centre height for the track. In my time in Baja, I have done calculations of the type for vehicles that had roughly the same weight distribution and wheelbases of approximately 1500 mm. [3] This includes braking, and deceleration (which is an acceleration at a negative rate). One important thing to notice is that its difficult to change total lateral load transfer by setup. The inertial force acting on the vehicle CG will generate a moment about the roll axis. [2] This would be more properly referred to as load transfer,[1][3] and that is the expression used in the motorcycle industry,[4][5] while weight transfer on motorcycles, to a lesser extent on automobiles, and cargo movement on either is due to a change in the CoM location relative to the wheels. g 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. 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. Hence: This is the total lateral load transfer on the car. The only way a suspension adjustment can affect weight transfer is to change the acceleration. With 250-lb/in front springs, the same 1000 pound weight transfer will lift the front end a total of two inches. The more F and the less m you have, the more a you can get.The third law: Every force on a car by another object, such as the ground, is matched by an equal and opposite force on the object by the car. That rationale comes from simple physics. 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). This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. weight is transferred in proportion to static weight. Weight transferis generally of far less practical importance than load transfer, for cars and SUVs at least. We now have roll moment arm and roll stiffnesses to play with. 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. is the longitudinal acceleration, The front and rear roll centres heights were kept equal, but varied from 3 mm to the CG height (254 mm). 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 overall effect will depend upon roll centre heights and roll stiffnesses, and a definitive conclusion will require a deeper analysis. The car has turned in towards the apex. Weight . A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. Keep in mind, the example we used is more typical for a circle track setup; in a road race vehicle, you'll likely be shooting for a more balanced left-weight percentage of 50 percent (although that is not always . This is an easy way to put something that is a complex interrelation of slip angles and weight transfer. Lets say the car is rear wheel drive with a rear weight distribution and large, lightly loaded tyres. Total lateral weight transfer is a combination of 3 distinct effects: Weight transfer of unsprung mass: Lateral force generated by the unsprung mass of the suspension and lateral. n Just like on asphalt, we have what is commonly referred to as Weight Transfer with dirt cars. Can you see the trend? Since these forces are not directed through the vehicle's CoM, one or more moments are generated whose forces are the tires' traction forces at pavement level, the other one (equal but opposed) is the mass inertia located at the CoM and the moment arm is the distance from pavement surface to CoM. Another reason to rule out changes in roll moment arm is that, because it directly multiplies the proportion of roll stiffnesses, it will have the same effect on both axles whether is to increase or decrease lateral load transfer. Well, a thousand changes to the car could be applied. Transition This is the point at which the car 'takes its set'. Here, the load transfer is increased by means of the lateral load transfer parameter, instead of the FLT. Let us expand that analysis by looking at the pair of tyres. Lets now see how these components affect each other and how they affect load transfer together. Figure 14 shows the contour plot. Weight transfer is the result of acceleration, braking or cornering. The trend in dirt racing seems to be leaning toward a left side weight percentage of around 53.5 to 55 and somewhere between 75 and 125 pounds of wedge. Bear in mind that all the analysis done here was for steady-state lateral load transfer, which is why dampers were not mentioned at all. The first point to stress again is that the overall load transfer that a car experiences, travelling on a circular path of radius R at constant velocity V (and, hence, with constant lateral acceleration Ay=V2/R) is always about the same, no matter what we do in terms of tuning. Your shock absorbers are considered after your ride and roll stiffness have been selected. This force will result in a moment, whose arm is the unsprung CG height, . Newtons third law requires that these equal and opposite forces exist, but we are only concerned about how the ground and the Earths gravity affect the car. But if total lateral load transfer is difficult to change once the car has been designed and built, then how can it be used to improve handling? And as discussed in Weight Transfer Part 2, the driving coach Rob Wilson talks weight transfer almost exclusively when he describes what he is teaching to drivers. By way of example, when a vehicle accelerates, a weight transfer toward the rear wheels can occur. Under hard braking it might be clearly visible even from inside the vehicle as the nose dives toward the ground (most of this will be due to load transfer). If you hold rear roll rate distribution constant at 54 % and increase roll centre height, lateral load transfer will have no significant change. The tendency of a car to keep moving the way it is moving is the inertia of the car, and this tendency is concentrated at the CG point. During cornering a lateral acceleration by the tire contact patch is created. Closed Wheel Race Cars How much does a NASCAR car weigh? {\displaystyle a} Typically a tensioned chain produces the rotational forces or torque. Lowering the CoM towards the ground is one method of reducing load transfer. Lateral load transfer in one axle will change with the proportion of the roll stiffnesses on that axle, not the roll stiffnesses themselves. 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. 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 . Term 2 always leads Term 3. Notice the smaller cornering potential for higher values of the lateral load transfer parameter. This fact can be explained at deeper levels, but such an explanation would take us too far off the subject of weight transfer. Increasing front roll center height increases weight transfer at front axle through suspension links (Term 2), but reduces overall weight transfer through suspension (Term 3). These effects are good for tightening up the car when winged down, but opposite for roll right. We wont consider subtleties such as suspension and tire deflection yet. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. This bias to one pair of tires doing more "work" than the other pair results in a net loss of total available traction. If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. When this happens, the outside spring of the suspension is compressed and the inside spring is extended. This conclusion is somehow trivial, as we know that roll moment arm decreases as roll axis gets closer to the sprung mass CG and roll rate distribution only affects the roll angle lateral load transfer component. This is generally not the first option to take because of the effect that it has on other aspects of the car. the kinematic and elastic components. is the change in load borne by the front wheels, Then, a series of steer angles in the range of interest is selected. . I have heard of many cars running well outside of these parameters and winning. For the tow vehicle, the chain pulls up on the weight distribution bar. Before we start this analysis, lets make some important definitions: Load transfer from direct force is one of the two components related to the lateral force acting upon the sprung mass. 500 - 1500 (400 - 1,100) The suspension roll stiffness calculation for K9 was in the order of 4,500 ft-lb/degree of roll. C. Despite increasing the steering angle, the car has taken a line which is not tight enough to take the turn. g The fact is that weight transfer is an unavoidable phenomenon that occurs whether or not a vehicle rolls. Now lets use the knowledge discussed here applied in the example presented at the beginning of this article, with a little more detail in it. Weight transfer during accelerating and cornering are mere variations on the theme. The RF tire is. is the center of mass height, Figure 7 shows the gearbox from Mercedes W05, 2014 Formula One champion. 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. From: Dr. Brian Beckmans The Physics of Racing. The same thing happens on the left . A. The lateral force of the track is the sum of lateral forces obtained from each tyre. If you represent multiple proportions, you will have multiple lines with different inclinations. This will give: Now consider , the vertical load on the outer tyre in a corner, and , the vertical load on the inner tyre. {\displaystyle m} Our system is proven to increase traction, and reduce fuel consumption and track maintenance. The car is not changing its motion in the vertical direction, at least as long as it doesnt get airborne, so the total sum of all forces in the vertical direction must be zero. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright . Learning to optimize weight transfer allows us to optimize the grip of the racecar. Literally, the rear end gets light, as one often hears racers say. This happens because raising the roll centre in any axle will approximate the roll axis to the sprung weight CG. Here, the lateral force acting on the sprung mass () will generate a moment on the tyres through the roll centre height that will also contribute to lateral load transfer. Total lateral weight transfer is a combination of 3 distinct effects: Lateral force generated by the unsprung mass of the suspension and lateral acceleration is reacted directly by the tires, giving rise to a vertical component defined as Fz1. any weight added, ballast, may not extend over the front or rear of the car's body or tires, and must be permanently attached to the vehicle, and there may be a maximum of 500 lbs ballast with a maximum of 100 lbs of that being removable. 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. It has increased importance when roll rate distribution in one track gets close to the weight distribution on that axle, as direct force component has its importance reduced (assuming horizontal roll axis). These numbers are just averages and are very dependent on the class of car and the tires being run. 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. Join a community of over 4000 clever racing enthusiasts that want to improve their knowledge on the technical side of motorsport! Figure 4 shows the forces and moments acting on the sprung CG. Notice that this is just one possibility and other parameters might be investigated as well. This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. If that was the case, you should work on the roll centres heights instead, and then adjust suspension parameters accordingly. This can be confirmed by adopting the conclusions from the analysis of figure 10, where we agreed that the gravity term is negligible for roll angle lateral weight transfer component. The rest of this article explains how inertia and adhesive forces give rise to weight transfer through Newtons laws. The Trackmobile Weight Transfer System is a hydraulic system developed to implement this idea in an intuitive and easy-to-use way. This force is then divided by the weight on the axle, This lateral acceleration is plotted against FLT, with reference steer angle as a parameter. Here they are the real heavyweights! Weight (or Load) Transfer Explained (Actionable Tutorial) Driver61 988K subscribers Subscribe 2K Share 93K views 5 years ago Welcome to tutorial five in our Driver's University Series. r Here, is the lateral acceleration in G units, is the weight of the car, is the CG height, is the track width and and are the vertical loads on the left and right tyres, respectively. The Physics of Racing Part 1: Weight Transfer, 10 Tips on How to Become a Pro Racing Driver, Michelin Raceway Road Atlanta Track Guide, Allen Berg Racing Schools Announce East Coast Expansion, Allen Berg to Speak at ADAS & Autonomous Vehicle Technology Expo.