what is weight transfer in a race car? what is weight transfer in a race car?

If you accelerate, brake or corner harder, you transfer more weight. It applies for all cars, especially racing, sports and high performance road cars. These effects are very important, but secondary. Do you see where this heading? 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). What happened here? or . The weight distribution is usually quoted in terms of percentage at the front vs back. 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 . The second option to alter load transfer from direct lateral force component is to change roll centre heights. Weight transfer is the result of acceleration, braking or cornering. But these forces are acting at ground level, not at the level of the CG. The weight transfer setup recognizes the importance of ride height and roll stiffness in determining a good balanced set up for the car. 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. 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 rest of this article explains how inertia and adhesive forces give rise to weight transfer through Newtons laws. 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. is the longitudinal acceleration, Imagine pulling a table cloth out from under some glasses and candelabra. It is easy to modify through the components and is where engineers usually make more adjustments specially between sessions or before the race. That is a lot of force from those four tire contact patches. 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. If it reaches half the weight of the vehicle it will start to roll over. 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. Weight transfer is an advanced techniqe which can impact the cart in four directions: front, back, and then each side of the kart. That rationale comes from simple physics. So, as expected, the car is not wedged. This component is the easier to control. The total weight of the vehicle does not change; load is merely transferred from the wheels at one end of the car to the wheels at the other end. 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. These adjustable bars generally have blade lever arms, as the one shown in figure 11. By way of example, when a vehicle accelerates, a weight transfer toward the rear wheels can occur. 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. For setup, we look into changing the lateral load transfer in one axle relative to the other, to affect balance. 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. 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? Weight transfers will occur in more controllable amounts, which will result in a more efficient and stable handling race car. More wing speed means we need to keep the right rear in further to get the car tighter. Hence: This is the total lateral load transfer on the car. An important attribute of the suspension is the Roll-centre. 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 analysis procedure is as follows: The potential diagram is a benchmarking of the performance that can be achieved by a pair of tyres. 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!). Figure 8 clarifies. For this analysis, only the rear axle was considered. f Roll stiffness is defined as the resistance moment generated per unit of roll angle of the sprung mass, and it has SI units of Nm/rad. Roll stiffness can be altered by either changing ride stiffness of the suspension (vertical stiffness) or by changing the stiffness of the antiroll bars. 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 . 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. Figure 4 shows the forces and moments acting on the sprung CG. 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. In a drag racing application, you want to narrow down the rate of the spring to the softest one you can run without having any coil bind. These objects would have a tendency to tip or rotate over, and the tendency is greater for taller objects and is greater the harder you pull on the cloth. This leads some to think that increasing roll centre heights will actually decrease weight transfer because it reduces roll. It is defined as the point at which lateral forces on the body are reacted by the suspension links. t Our system is proven to increase traction, and reduce fuel consumption and track maintenance. 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. 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. Read more Insert your e-mail here to receive free updates from this blog! The reason I'm asking you is because you're one of the bigger guys in the pit area. While a luxury town car will be supple and compliant over the bumps it will not be engineered to provide snappy turn-in, or weight transfer to optimize traction under power. The article begins with the elements and works up to some simple equations that you can use to calculate weight transfer in any car knowing only the wheelbase, the height of the CG, the static weight distribution, and the track, or distance between the tires across the car. 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. The distribution of dynamic loads can be altered with aerodynamics, with the regulation of wings or the static/dynamic height of the vehicle. So a ride height adjustment to your race car, or a roll centre geometry change is a very valid tuning device. The actual wheel loads are calculated for a series of FLT, which can go from 0 to 1.0, for the given track load. The lighter 250-lb/in rate benefits a drag car in two ways. 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. The hardest one would be to change the bar itself, though there are some antiroll bars that have adjustable stiffnesses, eliminating the need to replace bars. It can be varied simply by raising or lowering the roll centre relative to the ground. Referring back to the total load transfer equation, we see that the total weight transfer will be caused by inertial forces acting upon the entire mass of the car. Check stagger at each tire, even if using radials. The term is a gravity component that arises due to the sprung CG being shifted to the side when the chassis rolls. What we can do is only influence which portion of the total lateral . Figure 14 can lead us to very interesting conclusions. However, the suspension of a car will allow lateral load transfer to present itself in different ways and to be distributed between the axles in a controlled manner. 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. . Let's start by taking a look at four stages of understeer. 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. If you analyse figure 2, you will see that an increasing fraction load transfer will come together with a decreasing lateral force potential for the axle. This component of lateral load transfer is the least useful as a setup tool. Figure 3 shows the plot. 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. 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. w Under heavy or sustained braking, the fronts are . Before I explain this, let me talk about a good thing to understand the subject the steady-state analysis of a pair of tyres. 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. g Also, if you liked this post, please share it on Twitter or Facebook, and among your friends. Term 2 always leads Term 3. How can weight shift when everything is in the car bolted in and strapped down? Weight . Allen Berg ranks among Canada's top racing personalities. Then, most of the solutions available will be related to the subject of this post: lateral load transfer. 2. In the context of our racing application, they are: The first law:a car in straight-line motion at a constant speed will keep such motion until acted on by an external force. 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. 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 article explains the physics of weight transfer. During cornering a lateral acceleration by the tire contact patch is created. 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. Just like on asphalt, we have what is commonly referred to as Weight Transfer with dirt cars. Figure 7 shows the gearbox from Mercedes W05, 2014 Formula One champion. e The added axle weight will slow the release of the stretch in the tire and help hold traction longer. Use a 1/4 to one scale. A flatter car, one with a lower CG, handles better and quicker because weight transfer is not so drastic as it is in a high car. For the trailer, the chain pulls down . *This website is unofficial and is not associated in any way with the Formula One group of companies. G cannot be doing it since it passes right through the center of gravity. 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. 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 car should be at minimum weight, using ballast as needed to make the proper weight. If the car were standing still or coasting, and its weight distribution were 50-50, then Lf would be the same as Lr. Lets now see how these components affect each other and how they affect load transfer together. Turning in to a corner brings the car's momentum forward . 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. Acceleration causes the sprung mass to rotate about a geometric axis resulting in relocation of the CoM. 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. This button displays the currently selected search type. The figure only shows forces on the car, not forces on the ground and the CG of the Earth. Weight transfer is the most basic foundation of vehicle dynamics, yet holds many of the keys to ultimate car control. Now that we have quantified lateral load transfer on an axle, we can start to analyse how the individual components interact. Can you see the trend? 21 Shifting. the amount of body roll per unit of lateral acceleration: If we isolate the roll angle from the equation above, we can use it to calculate the moments from roll resistance moment and sprung CG side shift for a single axle. These lift forces are as real as the ones that keep an airplane in the air, and they keep the car from falling through the ground to the center of the Earth. 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. In wheeled vehicles, load transfer is the measurable change of load borne by different wheels during acceleration (both longitudinal and lateral). How much lead weight do you have on your car? NOTE: This information is from an NHRA Rule Book 2019 Addendum. Why? This makes changes in roll moment arm to control roll angle component useless. The previous weight of the car amounted to 2,425 pounds, while now it is about 2,335 pounds. Weight transfer is affected by the distance between the CG Height and the roll centre. 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). a 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 only way a suspension adjustment can affect weight transfer is to change the acceleration. 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. The driver is said to manage or control the weight transfer. Tire Offsets. 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). 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. i This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. An inexpensive set of shocks (such as the ones advertised as 50/50 or a three-way adjustable) should work on cars with as much as 300 to 350 . The fact is that weight transfer is an unavoidable phenomenon that occurs whether or not a vehicle rolls. As a result load transfer is reduced in both the longitudinal and lateral directions. These numbers are reported in shop manuals and most journalistic reviews of cars. As stated before, it is very difficult to change the total lateral load transfer of a car without increasing the track width or reducing either the weight or the CG height. If that was the case, you should work on the roll centres heights instead, and then adjust suspension parameters accordingly. 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). If you know the deep reasons why you ought to do certain things you will remember the things better and move faster toward complete internalization of the skills. 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. Fitting racing tires to a tall or narrow vehicle and then driving it hard may lead to rollover. is the acceleration of gravity, The lateral force of the track is the sum of lateral forces obtained from each tyre. 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. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. Putting weight on the front is achieved by lifting, turning, and/or braking. Last edited on 26 February 2023, at 00:40, https://en.wikipedia.org/w/index.php?title=Weight_transfer&oldid=1141628474, the change in load borne by different wheels of even perfectly rigid vehicles during acceleration, This page was last edited on 26 February 2023, at 00:40. 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. What happened? The amount the body rolls is affected by the stiffness of the springs/bars, and the speed of the roll is affected by the stiffness of the shocks. usually, production based race cars will not have any front bar at all, and rely stricly on proper spring rates . A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. From: Dr. Brian Beckmans The Physics of Racing. The calculations presented here were based on a vehicle with a 3125 mm wheelbase and 54% weight distribution on the rear axle, which are reasonable values for most race cars. 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. What would you do, in order to solve the problem? 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. 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. I make no claim that this would hold true for every car in the world, but if thats the case for vehicles with wheelbases as different as the ones Ive tried, than I wouldnt be surprised if it was for other cars. When expanded it provides a list of search options that will switch the search inputs to match the current selection. If , and will have the term inside brackets resulting in . Its not possible to conclude directly what influence increasing roll centre heights will have. 1. It is the process of shifting your body weight from one side of the kart to the other or leaning forward or back. By rotating the lever arms, its area moment of inertia in bending is changed, hence altering its stiffness. An outside observer might witness this as the vehicle visibly leans to the back, or squats. The input data were based on the manuals from the manufacturer of an important formula category. Here the gearbox has a removable carbon fibre structural outer sleeve, allowing changes in the design of the rear suspension without having to re-test the rear of the car for crashworthiness. 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. 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. 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. This is reacted by the roll stiffness (or roll rate), , of the car. An exception is during positive acceleration when the engine power is driving two or fewer wheels. 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. The change in this arm with roll centre heights will depend on the wheelbase and weight distribution. 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. 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). Weight transfer is the change in load borne by different wheels of even perfectly rigid vehicles during acceleration, and the change in center of mass location relative to the wheels because of suspension compliance or cargo shifting or sloshing. Figure 14 shows the contour plot. 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. 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. Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. Naturally, you're more inclined to wheelstand with an increase in acceleration. 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. G points down and counteracts the sum of Lf and Lr, which point up. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. 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 . {\displaystyle g} 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 %. In the post about lateral force from the tyres, we discussed tyre load sensitivity, the property that makes lateral force from a tyre to grow at a smaller rate with increasing vertical load. 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. A perfectly rigid vehicle, without suspension that would not exhibit pitching or rolling of the body, still undergoes load transfer. Figure 6 shows the CAD design of a similar gearbox, highlighting the different options for installing pickup points. It is always the case that Lf plus Lr equals G, the weight of the car. Weight transferis generally of far less practical importance than load transfer, for cars and SUVs at least. Queens GTO/Viper. Calculating the load transfer in a vehicle is fairly straightforward. The weight distribution on the rear axle was 54 %. The vehicle mass resists the acceleration with a force acting at its center of gravity. {\displaystyle m} Now do the same, but picking a front roll centre height and imagining a vertical line instead. 500 - 1500 (400 - 1,100) The suspension roll stiffness calculation for K9 was in the order of 4,500 ft-lb/degree of roll. As we move up to higher categories, the engineering gets more complex. This characteristic is also observed here. If you represent multiple proportions, you will have multiple lines with different inclinations. Total available grip will drop by around 6% as a result of this load transfer. 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). This is an easy way to put something that is a complex interrelation of slip angles and weight transfer. The effects of weight transfer are proportional to the height of the CG off the ground. The weight of an IndyCar race car should be at least 712 kg, with an average of 1630 lbs or 739.5 kg. I hope this article was useful to you, and that you have enjoyed reading it. 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. 3. Here the pickup points are highlighted for better comprehension. This component will, however, be altered by changes in other components (e.g. We need to recognise that not all the weight transfer goes via the springs, dampers and anti-roll bars. The analysis begins by taking the moment equilibrium about the roll axis: Where is the roll resistance moment, and is the roll moment. It arises from the force coupling effect that roll centres have, directly linking forces on sprung mass to the unsprung mass. 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. 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. 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. When a car leaves the starting line, acceleration forces create load transfer from the front to the rear. The softer the spring rate the more weight transfer you will see. 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. The vehicle's weight is transferred forwards and the front suspension compresses: 'compression'. Changing the moment generated by this component requires changes in either the unsprung mass or its 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. Steering. For the tow vehicle, the chain pulls up on the weight distribution bar. 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). . This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. When the car corners, lateral acceleration is applied at this CG, generating a centrifugal force. Weight Transfer - A Core of Vehicle Dynamics. The overall effect will depend upon roll centre heights and roll stiffnesses, and a definitive conclusion will require a deeper analysis. On limit conditions, this will translate in one of the axles breaking loose and skidding before the other. The same will not be true for the weight shift component, because the axle will only support the fraction of the sprung weight distributed to it. h 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. The forces upon the springs are reacted by the tyres, and that contributes to lateral load transfer. Thus, having weight transferred onto a tire increases how much it can grip and having weight transferred off a tire decreases how much it can grip the road. {\displaystyle w} 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.