what is weight transfer in a race car?

Calculating the load transfer in a vehicle is fairly straightforward. 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. A car weighs so much overall, and that is distributed - let's assume for the sake of argument, equally - between front and rear. It is the process of shifting your body weight from one side of the kart to the other or leaning forward or back. All these mechanisms generate a moment about the car that will translate into a vertical load difference between the inside and the outside tyres. This is an easy way to put something that is a complex interrelation of slip angles and weight transfer. How to Make a Winning Race Car Setup - Racing Car Dynamics Before we discuss how these moments are quantified, its interesting to derive a relation between a generic moment and the vertical load change between tyres separated by a distance . Drag Race Suspension Tuning - RacingJunk News Why? Transition This is the point at which the car 'takes its set'. Conversely, a supercar is built to approximate race geometry with few concessions to prevent spilling the drinks. With those values, the gravity term will be 1662.1 Nm. For context, we are experimenting with carbon-carbon brake discs on a non-downforce car. An important attribute of the suspension is the Roll-centre. : 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 splitting of the roll moment between front and rear axles is useful in analysing lateral load transfer and this is called roll moment distribution between front and rear axles. 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. Check stagger at each tire, even if using radials. 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. Front-back weight transfer is proportional to the change in the longitudinal location of the CoM to the vehicle's wheelbase, and side-to-side weight transfer (summed over front and rear) is proportional to the ratio of the change in the CoM's lateral location to the vehicle's track. What happened here? 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 . 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. 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. Bear in mind that the roll moment arm is the perpendicular distance between the CG of the sprung mass and the roll axis. is the acceleration of gravity, 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. . 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. 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. What happened? usually, production based race cars will not have any front bar at all, and rely stricly on proper spring rates . Weight Training: Everything You Need to Know About Race Car Weight But why does weight shift during these maneuvers? If your driver complies about oversteer in the slowest corners, it means that the front axle is generating higher lateral force than the rear. Here they are the real heavyweights! If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. Race Car Ride Height 101- With Jerry Bickel And Chassis - Dragzine Deceleration moves the center of gravity toward the front of the vehicle, taking weight out of the rear tires. The results were the same. Weight transfer is an advanced techniqe which can impact the cart in four directions: front, back, and then each side of the kart. This component of lateral load transfer is the least useful as a setup tool. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. Putting weight on the front is achieved by lifting, turning, and/or braking. When the car corners, lateral acceleration is applied at this CG, generating a centrifugal force. 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 The minimum weight of the car to take part in the X275 drag race is 2625 pounds. Dynamic Load Transfer - OzeBiz 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. Conversely, if you increase rear roll centre height, lateral load transfer increases on the rear axle and decreases on the front axle. The front wheels must steer, and possibly also drive. 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. 35% Front 420 lbs 780 lbs 280 lbs 520 lbs LH Turn - New Stiffer Front Roll Bar 33.3% If you accelerate, brake or corner harder, you transfer more weight. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each. As such, the most powerful cars are almost never front wheel drive, as the acceleration itself causes the front wheels' traction to decrease. Weight transfer issue | Bob's 4 Cycle Karting Same theory applies: moving the right rear in will add more static right rear weight and will cause more weight transfer. The amount of weight transfer is detirmined by how wide the track is (wider = less weight transfer) and how high the CG is (lower CG = less weight transfer). 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. Suspension Basics and Drag Racing Dynamics - Muscle Car DIY 2. draw the ground line ,vehicle center line and center of the left and right tire contact patches. 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. Weight transfers occur as a result of the chassis twisting around the car's roll centre, which determined by the natural suspension setup. 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. The car has turned in towards the apex. Tire Offsets. MichaelP. How Does Weight Distribution Affect Race Car Performance? Transient lateral load transfer is an important aspect of vehicle setup, but lets leave the discussion on that for another day. If , and will have the term inside brackets resulting in . 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). This will give: Now consider , the vertical load on the outer tyre in a corner, and , the vertical load on the inner tyre. Weight Transfer Equation - fx Solver Queens GTO/Viper. 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. What weight the front tires lose, the rear tires gain. [3] This includes braking, and deceleration (which is an acceleration at a negative rate). Weight transfer during cornering/braking : r/F1Technical - reddit Weight transfer in a car is a function of Lateral Acceleration, Track Width, Centre of Gravity Height (CG Height) and Weight. a When cornering, the sprung mass of the car will roll by an amount , the roll angle. A big tire car with a lot of power is going to transfer weight much . r When the driver gets on the brakes, the total remains the same . Then the expansion of the tire will begin to lift the car. Controlling Your Balance on the Road: Pitch, Roll and Yaw - e permit test This results in a reduced load on the vehicle rear axle and an increase on the front. At this moment, you should be convinced of the irrelevance of the gravity term on roll angle weight transfer component. "The ride height is meant to be in one spot you should look to move weight, adjust the shocks . Autocross to Win (DGs Autocross Secrets) - Weight Transfer Balancing a car is controlling weight transfer using throttle, brakes, and steering. Dynamic weight transfer in vehicle - SlideShare In conclusion, it was a huge effort by Tin . For you to get meaningful results from the equation above, you need to use consistent units. The reason is that the magnitude of these forces determines the ability of a tire to stick, and imbalances between the front and rear lift forces account for understeer and over-steer. 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. It's Worn Weight Loads and Forces for Dirt Cars h 20 - 25,000 (15 - 18,500) Formula SAE. 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. 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. For the SI system, the weights should be in N, the angular stiffnesses in Nm/rad, the lengths in m, and the acceleration is nondimensional (because we are dividing lateral acceleration by the acceleration of gravity). . The distribution of dynamic loads can be altered with aerodynamics, with the regulation of wings or the static/dynamic height of the vehicle. So, as expected, the car is not wedged. This force generates a lateral weight transfer in the opposite direction of the turn. These numbers are just averages and are very dependent on the class of car and the tires being run. What would you do, in order to solve the problem? 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. {\displaystyle m} 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. Figure 10 shows the plot of the roll angle component versus gravity term. 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. Weight transfers - Drivingfast.net Hence: This is the total lateral load transfer on the car. Now lets stop for a moment to analyse the influence of the gravity term on the lateral load transfer component. 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. 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!). Consider the front and rear braking forces, Bf and Br, in the diagram. 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 . 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). 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. This article uses this latter pair of definitions. 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. Weight Transfer: how it works and how to use it in setup The actual wheel loads are calculated for a series of FLT, which can go from 0 to 1.0, for the given track load. Weight transfer is the result of acceleration, braking or cornering. 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. 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? Dialing in Optimal Weight Distribution | Balancing Act - DSPORT Magazine The reason it is relevant is that the amount of weight on a tire directly affects how much grip is available from that tire. Understanding weight transfer is a fundamental skill that racecar drivers need to know. The RF tire is. The analysis procedure is as follows: The potential diagram is a benchmarking of the performance that can be achieved by a pair of tyres. Another method of reducing load transfer is by increasing the wheel spacings. Lowering the CoM towards the ground is one method of reducing load transfer. The term is a gravity component that arises due to the sprung CG being shifted to the side when the chassis rolls. The vehicle's weight is transferred forwards and the front suspension compresses: 'compression'. Well, a thousand changes to the car could be applied. Then, most of the solutions available will be related to the subject of this post: lateral load transfer. Figure 4 shows the forces and moments acting on the sprung CG. When a body rolls, the motion generates rotational torque which must be overcome every time we want to change direction. The reason I'm asking you is because you're one of the bigger guys in the pit area. 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. Just like on asphalt, we have what is commonly referred to as Weight Transfer with dirt cars. 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). The Physics Of Racing Part 1: Weight Transfer | ABRS 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. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. 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. 21 Shifting. Deceleration Weight Transfer The opposite of the acceleration weight transfer takes place during deceleration. At rest, or at a constant speed, the weight of the car could be measured by placing a set of scales under each tire. From: Dr. Brian Beckmans The Physics of Racing. 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. 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. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. Inside percentages are the same front and rear. The diagonal lines represent lateral force potential for constant values, whereas the curved lines show values obtained for a constant reference steer angle. The moment equilibrium analysis will be the same here, but we will substitute the moment from the inertial force about the CG, , by a generic moment, . Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. The front and rear roll centres heights were kept equal, but varied from 3 mm to the CG height (254 mm). Conversely, if you hold roll centre heights at about 254 mm and vary rear roll rate distribution, lateral load distribution wont suffer relevant differences. Stock Car Racing Weight Distribution Importance - MotorTrend 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. If the car were standing still or coasting, and its weight distribution were 50-50, then Lf would be the same as Lr. Weight Transfer - Formula 1 Dictionary Senior Vehicle Dynamics Engineer providing VD simulation support for Multinational Automakers. 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 %. When a car leaves the starting line, acceleration forces create load transfer from the front to the rear. D. Newtons second law explains why quick cars are powerful and lightweight. This component will, however, be altered by changes in other components (e.g. is the total vehicle mass, and By rotating the lever arms, its area moment of inertia in bending is changed, hence altering its stiffness. The fact is, by increasing the roll centre height in one axle, you are increasing lateral load transfer from the direct lateral force component, while at the same time you are decreasing lateral load transfer from roll angle component. This is multiplied by the cosine of the reference steer angle, to obtain a lateral force in the direction of the turning centre. 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. Adjustable Damping Suspension Tuning Guide - corneringperformance.com 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. 1. We wont consider subtleties such as suspension and tire deflection yet. The following formula calculates the amount of weight transfer: Weight transfer = ( Lateral acceleration x Weight x Height of CG ) / Track width If unsprung mass is isolated, its possible to find its own CG. Weight transfer is the most basic foundation of vehicle dynamics, yet holds many of the keys to ultimate car control. Understanding Weight Transfer and Racecar Dynamics - NASA Speed News i The driver has hit the apex but has found the car is starting to push wide of the desired line. See you soon! is the change in load borne by the front wheels, Friction comes from the tires on the ground and the air flowing over the car. Roll stiffnesses were input in the form of roll rate distribution, varying from 0 to 1. 3. Weight transfer -Draglist.com Drag Racing 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. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. Where is the roll angle caused by the suspension compliances and K is the suspension roll stiffness. It is always the case that Lf plus Lr equals G, the weight of the car. 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. 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. Turning in to a corner brings the car's momentum forward . Lets say that you are a race engineer and your driver is having trouble to go around the slowest corners on the circuit. 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. Roll stiffness can be altered by either changing ride stiffness of the suspension (vertical stiffness) or by changing the stiffness of the antiroll bars. This is altered by moving the suspension pickups so that suspension arms will be at different position and/or orientation. Weight transfer is affected by the distance between the CG Height and the roll centre. In a dirt race car, our setups determine where the weight that has transferred goes. "Right now, none. 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. Weight transfer occurs as the vehicle's CoM shifts during automotive maneuvers. . 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. Most autocrossers and race drivers learn early in their careers the importance of balancing a car. You have less lead to work with. Vertical load is the load actually seen at the tire contact patch. From the general lateral load transfer equation, we know that this component is changed by modifications to either the weight distribution of the car, or the roll centres height. If you represent multiple proportions, you will have multiple lines with different inclinations. Racing Skills In 60 Seconds - Weight Transfer | Blayze Weight transfer has two components: Unsprung Weight Transfer: This is the contribution to weight transfer from the unsprung mass of the car. Balance of roll damping will further modify the handling during transient part of maneuver. 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. {\displaystyle \Delta Weight_{front}} One important thing to notice is that its difficult to change total lateral load transfer by setup. 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). Balancing a car is controlling weight transfer using throttle, brakes, and steering. Rethink Dirt: Advanced Dirt Track Theory | Hyper Racing Weight distribution can be controlled through positioning of ballast in the car. Weight transfer during cornering can be analysed in a similar way, where the track of the car replaces the wheelbase and d is always 50% (unless you account for the weight of 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. 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. Term 2 always leads Term 3. The front end will move faster and farther because less force is required to initially extend the spring. It is easy to modify through the components and is where engineers usually make more adjustments specially between sessions or before the race. Understanding corner weights | Articles | Grassroots Motorsports 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 . 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. 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 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 . G is the force of gravity that pulls the car toward the center of the Earth. B. So far, we have discussed the influence of each component in lateral load transfer in isolation. As you see, when we increase front roll centre height, the lateral weight transfer decreases on the rear axle while increasing on the front. e In figure 3 the effect is repeated, but from a different perspective. Load transfer causes the available traction at all four wheels to vary as the car brakes, accelerates, or turns. Lets now see how these components affect each other and how they affect load transfer together. It arises from the force coupling effect that roll centres have, directly linking forces on sprung mass to the unsprung mass. For this case, roll moment arm decrease with roll centre heights was smaller than the increase in roll centre heights themselves. 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. This means the driver should be in the car, all fluids topped up, and the fuel load should be such that the car makes your minimum weight rule at the designated time-usually after a race. 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. Another example would be the effect of ride stiffness on wheel hop frequency. 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. One g means that the total braking force equals the weight of the car, say, in pounds. is the total vehicle weight.[7][8]. 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). is the longitudinal acceleration, I hope this article was useful to you, and that you have enjoyed reading it.