what is weight transfer in a race car?

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. f Now lets analyse what happens when roll centre heights get close to the CG height. Roll is simply the effect of a suspension reacting to weight transfer. Deceleration Weight Transfer The opposite of the acceleration weight transfer takes place during deceleration. Even purpose-built cars, like a contemporary Pro Stocker, have more weight on the front-end than the back. Then the expansion of the tire will begin to lift the car. Balancing a car is controlling weight transfer using throttle, brakes, and steering. This happens because raising the roll centre in any axle will approximate the roll axis to the sprung weight CG. Put the driver weight in the car, preferably the driver. The thing is, roll is only one part of the equation, and as the discussion on this post will show, increasing roll centre height might either increase or decrease the lateral load transfer, depending on other parameters. : a go-kart), the weight transfer should split between F/R axles according to the CG position, just like you instinctively done for the longitudinal acceleration. "The ride height is meant to be in one spot you should look to move weight, adjust the shocks . Figure 1 . We now have roll moment arm and roll stiffnesses to play with. We define the Fraction Load Transfer, FLT, as the ratio between the difference to the weight on the axle: The parameter represents the total moment in the track about a point on the ground. 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. This is generally not the first option to take because of the effect that it has on other aspects of the car. For the trailer, the chain pulls down . The reason it is relevant is that the amount of weight on a tire directly affects how much grip is available from that tire. For you to get meaningful results from the equation above, you need to use consistent units. Weight distribution can be controlled through positioning of ballast in the car. At this moment, you should be convinced of the irrelevance of the gravity term on roll angle weight transfer component. In the previous post about understeer and oversteer, we have addressed the vehicle as the bicycle model, with its tracks compressed to a single tyre. For instance in a 0.9g turn, a car with a track of 1650 mm and a CoM height of 550 mm will see a load transfer of 30% of the vehicle weight, that is the outer wheels will see 60% more load than before, and the inners 60% less. 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. These effects are very important, but secondary. It is easy to modify through the components and is where engineers usually make more adjustments specially between sessions or before the race. Let us expand that analysis by looking at the pair of tyres. When cornering, the sprung mass of the car will roll by an amount , the roll angle. What would you do, in order to solve the problem? Steering. 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. Before I explain this, let me talk about a good thing to understand the subject the steady-state analysis of a pair of tyres. If the car were standing still or coasting, and its weight distribution were 50-50, then Lf would be the same as Lr. {\displaystyle g} Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. 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. Notice that this conclusion doesnt necessarily hold true for different roll axis inclinations. 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. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. Transient lateral load transfer is an important aspect of vehicle setup, but lets leave the discussion on that for another day. Newtons second law explains why quick cars are powerful and lightweight. The reason I'm asking you is because you're one of the bigger guys in the pit area. This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. If , and will have the term inside brackets resulting in . The car should be at minimum weight, using ballast as needed to make the proper weight. Any time you apply brakes, add or remove steering, and manipulate the. Front roll stiffness distribution only modifies Term 3 and hence increasing front roll stiffness always increases understeer. The amount of longitudinal load transfer that will take place due to a given acceleration is directly proportional to the weight of the vehicle, the height of its center of gravity and the rate of . Load transfer causes the available traction at all four wheels to vary as the car brakes, accelerates, or turns. As we move up to higher categories, the engineering gets more complex. G is the force of gravity that pulls the car toward the center of the Earth. 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. The forces upon the springs are reacted by the tyres, and that contributes to lateral load transfer. You have less lead to work with. [6] By simply raising or lowering the couplers, our machines can gain thousands of pounds for traction. By rotating the lever arms, its area moment of inertia in bending is changed, hence altering its stiffness. 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. The vehicle mass resists the acceleration with a force acting at its center of gravity. Conversely, if you increase rear roll centre height, lateral load transfer increases on the rear axle and decreases on the front axle. These are fundamental laws that apply to all large things in the universe, such as cars. 2. draw the ground line ,vehicle center line and center of the left and right tire contact patches. From our previous discussion on direct force weight transfer component, you know that to change roll moment arm you need to play with roll centre heights, which will ultimately affect that weight transfer component in the opposite way you want. This is reacted by the roll stiffness (or roll rate), , of the car. Weight transfer and load transfer are two expressions used somewhat confusingly to describe two distinct effects:[1]. Now you know why weight transfer happens. Conversely, a supercar is built to approximate race geometry with few concessions to prevent spilling the drinks. Both of these changes will involve adding, removing or repositioning mass (and therefore parts) within the unsprung part of the car. Weight . Figure 3 shows the plot. This article explains the physics of weight transfer. The change in this arm with roll centre heights will depend on the wheelbase and weight distribution. Calculating the load transfer in a vehicle is fairly straightforward. Load transfer is a crucial concept in understanding vehicle dynamics. More wing speed means we need to keep the right rear in further to get the car tighter. 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. The fact that the problem occurs in the slowest bits of the circuit might rule out the possibility of aerodynamic changes as a solution. The front end will move faster and farther because less force is required to initially extend the spring. For instance in a 0.9g turn, a car with a track of 1650mm and a CoM height of 550mm will see a load transfer of 30% of the vehicle weight, that is the outer wheels will see 60% more load than before, and the inners 60% less. Now that we know the best ways to change roll stiffness, lets see how it affects lateral load transfer. is the change in load borne by the front wheels, A. This is an easy way to put something that is a complex interrelation of slip angles and weight transfer. Figure 14 can lead us to very interesting conclusions. Location: Orlando, FL. What weight the front tires lose, the rear tires gain. Let's start by taking a look at four stages of understeer. 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. This moment is called roll moment or roll couple, , because it is responsible for body roll. The second term can be changed modifying the suspension geometry, usually difficult or not allowed in some competitions. There are Four Rules of Weight Transfer, Three lesser, one greater: Lesser the First: Turning the car will weight the outside wheels heavily, the inside wheels lightly. The total lateral load transfer on the car can be calculated from its free body diagram, as shown in figure 1. In a dirt race car, our setups determine where the weight that has transferred goes. When this happens, the outside spring of the suspension is compressed and the inside spring is extended. 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. 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. Perfect balance would thus be 50/50, and front weight distribution would be 60/40 and so on. 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. Then if the car is still loose on entry we start moving the weight, at the new height, to the right. 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. Then, a series of steer angles in the range of interest is selected. These adjustable bars generally have blade lever arms, as the one shown in figure 11. Liquids, such as fuel, readily flow within their containers, causing changes in the vehicle's CoM. 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. When you apply the brakes, you cause the tires to push forward against the ground, and the ground pushes back. The input data were based on the manuals from the manufacturer of an important formula category. The rest of this article explains how inertia and adhesive forces give rise to weight transfer through Newtons laws. The effects of weight transfer are proportional to the height of the CG off the ground. The weight distribution on the rear axle was 54 %. 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. 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. Consider the front and rear braking forces, Bf and Br, in the diagram. This leads as to believe that the roll centre height gain is higher than the decrease in the roll moment arm . 3. Postby BillyShope Wed Aug 22, 2007 5:48 am. Lf is the lift force exerted by the ground on the front tire, and Lr is the lift force on the rear tire. So, as expected, the car is not wedged. 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. If we use , the remaining roll angle component will be: If we keep the roll moment arm constant, then roll angle lateral load transfer component in one track will obviously be a function of the ratio between the roll stiffness on that track and the total roll stiffness of the car. 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. The overall effect will depend upon roll centre heights and roll stiffnesses, and a definitive conclusion will require a deeper analysis. 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. 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. 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. So a ride height adjustment to your race car, or a roll centre geometry change is a very valid tuning device. {\displaystyle b} This can be done in multiple ways. In that case, changing roll rate distribution or roll centre heights will have little effect in the balance, and other alternatives must be looked at, such as adjusting tyre pressures, tyre size and/or width or moving CG location (so that the inertial forces will be different in each axle). In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. 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. 1. I hope this article was useful to you, and that you have enjoyed reading it. Figure 10 shows the plot of the roll angle component versus gravity term. This law is expressed by the famous equation F = ma, where F is a force, m is the mass of the car, and a is the acceleration, or change in motion, of the car. These numbers are just averages and are very dependent on the class of car and the tires being run. At the same time, the CoM of the vehicle will typically move laterally and vertically, relative to the contact patch by no more than 30mm, leading to a weight transfer of less than 2%, and a corresponding reduction in grip of 0.01%. Moving weight should be used as a fine-tuning tool to get the car working as best it can for the track conditions. b 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. For this case, roll moment arm decrease with roll centre heights was smaller than the increase in roll centre heights themselves. Bear in mind that the lateral acceleration obtained from a specific fraction load transfer value will not necessarily cause the correspondent load transfer on the axle. 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. usually, production based race cars will not have any front bar at all, and rely stricly on proper spring rates . In general, it is almost safe to say that the Indycar weighs less than a Formula 1 car. 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. In cases where the performance of a pair of tyres is being analysed without regards to a particular vehicle, the parameter is a convenient way to represent changes in lateral load transfer. When we corner on a circle track turning left, the lateral forces will transfer some of the weight that was resting on the left side tires over onto the right side tires. Read more Insert your e-mail here to receive free updates from this blog! As with most race car parts, you get what you pay for. 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). This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. For a more comprehensive analysis, the effects from suspension geometry such as steer and camber variations due to ride, roll, braking, accelerating, lateral force compliance or aligning torque compliance, can be introduced before entering tyre data. Why? The added axle weight will slow the release of the stretch in the tire and help hold traction longer. 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. It is always the case that Lf plus Lr equals G, the weight of the car. The following weight transfers apply only to the sprung mass of the race car:-Sprung weight transfer via the roll centres (WTRC): Again, weight transfer is seperate for front and rear. Put an R-compound DOT tire on the same car and raise that force to 1.05 g of cornering force. Lets repeat the weight transfer equation here to make things easier: By looking at the equation, you can see that the weight transfer component from roll angle can be altered by changes in front or rear roll stiffnesses, roll moment arm or weight distribution. 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 . This. Here, the load transfer is increased by means of the lateral load transfer parameter, instead of the FLT. One important thing to notice is that its difficult to change total lateral load transfer by setup. The results were the same. The lighter 250-lb/in rate benefits a drag car in two ways. 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. This is given by: Here, is the sprung weight distribution to the axle being analysed and is the roll centre height for the track. 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. If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. 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. 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. One thing we can tell without any deep analysis is that increasing the roll centre height in one axle decreases the lateral weight transfer on the opposite axle, everything else kept constant. Join a community of over 4000 clever racing enthusiasts that want to improve their knowledge on the technical side of motorsport! The lateral force of the track is the sum of lateral forces obtained from each tyre. So a ride height adjustment to your race car, or a roll centre geometry . Bear in mind that the roll moment arm is the perpendicular distance between the CG of the sprung mass and the roll axis. Likewise, accelerating shifts weight to the rear, inducing under-steer, and cornering shifts weight to the opposite side, unloading the inside tires. Inside percentages are the same front and rear. Typically a tensioned chain produces the rotational forces or torque. "Right now, none. Now do the same, but picking a front roll centre height and imagining a vertical line instead. It may be a more practical way to assess vehicle handling in comparison to computer modelling, since the goal is generally to increase the lateral force on either the front or rear track.