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. The lateral force of the track is the sum of lateral forces obtained from each tyre. At this point, tyre data is entered and lateral force for each tyre in the axle is calculated taking into account the effects described above (if the case demands it). A. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. Well, a thousand changes to the car could be applied. That is a lot of force from those four tire contact patches. C. Despite increasing the steering angle, the car has taken a line which is not tight enough to take the turn. 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. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright . In this figure, the black and white pie plate in the center is the CG. The lateral load transfer parameter. It arises from the force coupling effect that roll centres have, directly linking forces on sprung mass to the unsprung mass. 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. If you hold rear roll rate distribution constant at 54 % and increase roll centre height, lateral load transfer will have no significant change. For the sake of example, ride stiffness controls ride height, which has strong effects on aerodynamics of ground effect cars (almost every race car with relevant aerodynamics design). So far, we have discussed the influence of each component in lateral load transfer in isolation. Understanding weight transfer is a fundamental skill that racecar drivers need to know. 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. Weight transfer during accelerating and cornering are mere variations on the theme. 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. Since springs are devices that generate forces upon displacements, a force on each spring arises, and these forces generate a moment that tends to resist the rotation of the body. 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. The following information applies to NASCAR-style Stock Cars; it may also be useful to production-based sports car racers with the engine in the front and the drive wheels in the back. b This is generally not the first option to take because of the effect that it has on other aspects of the car. Weight transfer and load transfer are two expressions used somewhat confusingly to describe two distinct effects:[1]. 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. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. replacement of brake cooling ducts for a lighter/heavier version). 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. The following formula calculates the amount of weight transfer: Weight transfer = ( Lateral acceleration x Weight x Height of CG ) / Track width The forces upon the springs are reacted by the tyres, and that contributes to lateral load transfer. 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. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. 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. The minimum weight of the car to take part in the X275 drag race is 2625 pounds. Learning to do it consistently and automatically is one essential part of becoming a truly good driver. Deceleration. 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. It can be varied simply by raising or lowering the roll centre relative to the ground. So, as expected, the car is not wedged. is the total vehicle mass, and the kinematic and elastic components. The major forces that accelerate a vehicle occur at the tires' contact patches. It is what helps us go fast! Weight transfer has two components: Unsprung Weight Transfer: This is the contribution to weight transfer from the unsprung mass of the car. As such, the most powerful cars are almost never front wheel drive, as the acceleration itself causes the front wheels' traction to decrease. h This will have a net effect of decreasing the lateral force generated by an axle when the load transfer on it increases. Direct force component or kinematic component useful as a setup tool, especially when roll axis is close to the sprung CG, and the influence of roll component is reduced. Weight . Steering towards the left or right moves the vehicle's center of gravity in the opposite direction, taking weight out of the left or right tires respectively. If that was the case, you should work on the roll centres heights instead, and then adjust suspension parameters accordingly. This is multiplied by the cosine of the reference steer angle, to obtain a lateral force in the direction of the turning centre. Briefly, the reason is that inertia acts through the center of gravity (CG) of the car, which is above the ground, but adhesive forces act at ground level through the tire contact patches. Our system is proven to increase traction, and reduce fuel consumption and track maintenance. Its not possible to conclude directly what influence increasing roll centre heights will have. . Changing the moment generated by this component requires changes in either the unsprung mass or its CG height. Then, most of the solutions available will be related to the subject of this post: lateral load transfer. 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. These effects are good for tightening up the car when winged down, but opposite for roll right. G is the force of gravity that pulls the car toward the center of the Earth. The weight distribution is usually quoted in terms of percentage at the front vs back. 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. The reason it is relevant is that the amount of weight on a tire directly affects how much grip is available from that tire. The distribution of dynamic loads can be altered with aerodynamics, with the regulation of wings or the static/dynamic height of the vehicle. An outside observer might witness this as the vehicle visibly leans to the back, or squats. As fuel is consumed, not only does the position of the CoM change, but the total weight of the vehicle is also reduced. 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. In a pair analysis, steady-state lateral force is obtained for the tyres on a track (front or rear pair), through data from a single tyre. 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. Weight transfer is the result of acceleration, braking or cornering. 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. What weight the front tires lose, the rear tires gain. One way to calculate the effect of load transfer, keeping in mind that this article uses "load transfer" to mean the phenomenon commonly referred to as "weight transfer" in the automotive world, is with the so-called "weight transfer equation": where Both of these changes will involve adding, removing or repositioning mass (and therefore parts) within the unsprung part 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. 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. You must learn how different maneuvers . is the total vehicle weight.[7][8]. The more the body rolls and the faster the body rolls, the more rotational . An important attribute of the suspension is the Roll-centre. It is these moments that cause variation in the load distributed between the tires. Now that we know the best ways to change roll stiffness, lets see how it affects lateral load transfer. This is a complex measure because it requires changes in suspension geometry, and it has influence on all geometry-related parameters, such as camber and toe gain, anti-pitch features and so on. However, the pitching and rolling of the body of a non-rigid vehicle adds some (small) weight transfer due to the (small) CoM horizontal displacement with respect to the wheel's axis suspension vertical travel and also due to deformation of the tires i.e. These numbers are just averages and are very dependent on the class of car and the tires being run. The braking forces create a rotating tendency, or torque, about the CG. By way of example, when a vehicle accelerates, a weight transfer toward the rear wheels can occur. For this analysis, only the rear axle was considered. Now do the same, but picking a front roll centre height and imagining a vertical line instead. The car has turned in towards the apex. Roll is simply the effect of a suspension reacting to weight transfer. This is why sports cars usually have either rear wheel drive or all wheel drive (and in the all wheel drive case, the power tends to be biased toward the rear wheels under normal conditions). Vertical load is the load actually seen at the tire contact patch. If you represent multiple proportions, you will have multiple lines with different inclinations. When a body rolls, the motion generates rotational torque which must be overcome every time we want to change direction. Any time you apply brakes, add or remove steering, and manipulate the. So a ride height adjustment to your race car, or a roll centre geometry change is a very valid tuning device. To further expand our analysis, lets put the theory into practice. In that case, the tires on the right side of the car are going to be on the outside of the corner many more times than the left side tires. Do you see where this heading? Because of this interaction with the springs, this component is also referred as the elastic weight transfer component. Antiroll bars are generally added to the car to make it stiffer in roll without altering the ride characteristics. This fact can be explained at deeper levels, but such an explanation would take us too far off the subject of weight transfer. This basically rules out weight distribution as a way of controlling roll angle component. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each. If unsprung mass is isolated, its possible to find its own CG. The actual wheel loads are calculated for a series of FLT, which can go from 0 to 1.0, for the given track load. Increasing the vehicle's wheelbase (length) reduces longitudinal load transfer while increasing the vehicle's track (width) reduces lateral load transfer. Let us expand that analysis by looking at the pair of tyres. Because of Newtons first law. This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. The analysis begins by taking the moment equilibrium about the roll axis: Where is the roll resistance moment, and is the roll moment. For the tow vehicle, the chain pulls up on the weight distribution bar. The location of the components of a vehicle is essential to achieve an ideal weight distribution and it depends on the following factors: Location of Components (Engine-Transmission-Pilot-Mechanical Components, fuel tank). This is characterised by the green region in the graph. 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. B. Notice the smaller cornering potential for higher values of the lateral load transfer parameter. In wheeled vehicles, load transfer is the measurable change of load borne by different wheels during acceleration (both longitudinal and lateral). We wont consider subtleties such as suspension and tire deflection yet. 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. [6] Allen Berg ranks among Canada's top racing personalities. [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. We'll assume the car's side to side weight distribution is equal. First notice that there are two particular regions in the plot, where any changes to one of the components will produce no sensitive effect on weight transfer. Literally, the rear end gets light, as one often hears racers say. 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. What would you do, in order to solve the problem? This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. Newtons second law explains why quick cars are powerful and lightweight. 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. Balance of roll damping will further modify the handling during transient part of maneuver. The Trackmobile Weight Transfer System is a hydraulic system developed to implement this idea in an intuitive and easy-to-use way. For context, we are experimenting with carbon-carbon brake discs on a non-downforce car. It is always the case that Lf plus Lr equals G, the weight of the car. Performance Engineer, withexperience in IMSA LMP2, Porsche Cup Brazil and othercategories. This force generates a lateral weight transfer in the opposite direction of the turn. A perfectly rigid vehicle, without suspension that would not exhibit pitching or rolling of the body, still undergoes load transfer. This will tell us that lateral load transfer on a track will become less dependent on the roll rate distribution on that track as the roll axis gets close to the CG of the sprung mass. This analysis may even be used to prepare tyre data, in order to make the bicycle model more realistic. So a ride height adjustment to your race car, or a roll centre geometry . Figure 14 can lead us to very interesting conclusions. Location: Orlando, FL. This will give: Now consider , the vertical load on the outer tyre in a corner, and , the vertical load on the inner tyre. Just like on asphalt, we have what is commonly referred to as Weight Transfer with dirt cars. Read more Insert your e-mail here to receive free updates from this blog! If your driver complies about oversteer in the slowest corners, it means that the front axle is generating higher lateral force than the rear. Some race cars have push-pull cables connected to the bars that allow the driver to change roll stiffnesses from inside the car. Lets analyse the moment involved in roll. 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? Try this exercise: pick whatever value you want for rear roll centre height, and imagine an horizontal line passing through the point correspondent to that value in both graphs, and observe how weight transfer changes along this line in both graphs (remember each graph represents an axle). This puts more load on the back tires and simultaneously increases traction. If you represent the rear roll stiffness as proportion of front roll stiffness in a line plot, the result will be a straight line, with an inclination equal to the proportion between the roll stiffnesses. 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. Go to YouTube and look up a slow-motion video of a drag race car leaving the line and watch the left rear tire. Steering. 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. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. These adjustable bars generally have blade lever arms, as the one shown in figure 11. The simplest component of load transfer is the one related to unsprung mass. Weight transfer occurs as the vehicle's CoM shifts during automotive maneuvers. For example, if the weight is shifted forward, the front tyres may be overloaded under heavy braking, while the rear tyres may lose most of their vertical load, reducing the brake capability of the car. As you see, when we increase front roll centre height, the lateral weight transfer decreases on the rear axle while increasing on the front. The second option to alter load transfer from direct lateral force component is to change roll centre heights. For you to get meaningful results from the equation above, you need to use consistent units. Conversely, if you hold roll centre heights at about 254 mm and vary rear roll rate distribution, lateral load distribution wont suffer relevant differences. "The ride height is meant to be in one spot you should look to move weight, adjust the shocks . 21 Shifting. It is defined as the point at which lateral forces on the body are reacted by the suspension links. Then, a series of steer angles in the range of interest is selected. A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. Refer again to figure 1. 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. The reason I'm asking you is because you're one of the bigger guys in the pit area. If it reaches half the weight of the vehicle it will start to roll over. 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. Join a community of over 4000 clever racing enthusiasts that want to improve their knowledge on the technical side of motorsport! Effect of downforce on weight transfer during braking - posted in The Technical Forum: Apologies if the answer to this is obvious, but I am trying to get a sense of whether weight transfer under braking is affected by how much downforce a car has. 3. 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%. For setup, we look into changing the lateral load transfer in one axle relative to the other, to affect balance. Usually, I'll have 50-80 lbs," Bloomquist told RacingNews.co from Lucas Oil Speedway a few weeks back. This leads as to believe that the roll centre height gain is higher than the decrease in the roll moment arm . This component of lateral load transfer is the least useful as a setup tool. This reduces the weight on the rear suspension causing it to extend: 'rebound'. Most autocrossers and race drivers learn early in their careers the importance of balancing a car. When the vehicle is cornering, the centrifugal force from inertia generates a moment that makes the sprung mass roll to the outside of the corner. Weight transfers will occur in more controllable amounts, which will result in a more efficient and stable handling race car. 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. In order words, the goal would be to reduce lateral load transfer in the rear axle in comparison to the front axle. 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). Your shock absorbers are considered after your ride and roll stiffness have been selected. The initial lurch will sink the car. NOTE: This information is from an NHRA Rule Book 2019 Addendum. The tires and chassis will also make a difference in the spring selection. Weight transfer varies depending on what the car is doing. A more in-depth discussion on how each of these moments are generated will now be presented. One important thing to notice is that its difficult to change total lateral load transfer by setup. 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.
Todd Murphy Rocky River, Articles W
Todd Murphy Rocky River, Articles W