what is weight transfer in a race car?

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. 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. 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. How can weight shift when everything is in the car bolted in and strapped down? See you soon! 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. Now you know why weight transfer happens. For the tow vehicle, the chain pulls up on the weight distribution bar. The term between brackets in the equation above is the roll rate distribution or roll stiffness distribution for a given axle, and it will ultimately control the elastic lateral load transfer component. Do you see how small it is compared to the roll stiffness of the car? The same thing happens on the left . Lets now see how these components affect each other and how they affect load transfer together. g Weight transfer varies depending on what the car is doing. If that was the case, you should work on the roll centres heights instead, and then adjust suspension parameters accordingly. 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. 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 analysis procedure is as follows: The potential diagram is a benchmarking of the performance that can be achieved by a pair of tyres. 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. The major forces that accelerate a vehicle occur at the tires' contact patches. This. 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. Lets say the car is rear wheel drive with a rear weight distribution and large, lightly loaded tyres. The input data were based on the manuals from the manufacturer of an important formula category. With those values, the gravity term will be 1662.1 Nm. Where is the roll angle caused by the suspension compliances and K is the suspension roll stiffness. When this happens, the outside spring of the suspension is compressed and the inside spring is extended. Crutches: Weight Distribution And Weight Transfer - MotorTrend 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. 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. Perfect balance would thus be 50/50, and front weight distribution would be 60/40 and so on. This curve is called the cornering coefficient curve for the track. 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. The lateral load transfer parameter. This reduces the weight on the rear suspension causing it to extend: 'rebound'. Assuming a 120" wb, 100lbs added 5' behind the rear axle will add 150lbs to the rear axle's scale weight, and take 50lbs off of the front axle. Sprung Weight Transfer: This is the contribution to weight transfer from the sprung mass of the car, which itself is broken into two sub-components: 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. Balancing a Dirt Stock Car Part 1 - Hogan Technologies If you accelerate, brake or corner harder, you transfer more weight. Conversely, if you increase rear roll centre height, lateral load transfer increases on the rear axle and decreases on the front axle. Increasing the vehicle's wheelbase (length) reduces longitudinal load transfer while increasing the vehicle's track (width) reduces lateral load transfer. [3] This includes braking, and deceleration (which is an acceleration at a negative rate). Understanding corner weights | Articles | Grassroots Motorsports 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. For the trailer, the chain pulls down . In this situation where all the tires are not being utilized load transfer can be advantageous. 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. 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. The RF tire is. This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. *This website is unofficial and is not associated in any way with the Formula One group of companies. Spring Into Action: How To Select Front Springs For Drag Racing - Dragzine 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. 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. The net loss can be attributed to the phenomenon known as tire load sensitivity. 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. 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. In general, it is almost safe to say that the Indycar weighs less than a Formula 1 car. Bickel explains how the way the 4-link plays into how you adjust the car. If your driver complies about oversteer in the slowest corners, it means that the front axle is generating higher lateral force than the rear. Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. A reference steer angle, which is the average of steer angles of both wheels on the axle, is specified (but the individual slip angles are used when entering the data). 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. t What weight the front tires lose, the rear tires gain. Weight transfer happens when a car's weight moves around its roll centre when braking, turning or accelerating. Weight . 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. 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. Turning in to a corner brings the car's momentum forward . The weight transfer is caused by rotational forces centered at the hitch ball. Figure 14 can lead us to very interesting conclusions. What happened? The only way a suspension adjustment can affect weight transfer is to change the acceleration. This will have a net effect of decreasing the lateral force generated by an axle when the load transfer on it increases. The lighter 250-lb/in rate benefits a drag car in two ways. Dialing in Optimal Weight Distribution | Balancing Act - DSPORT Magazine But it must be considered that the Mustang at this time does not mount the carbon bottles, and there's no driver inside. 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. Even purpose-built cars, like a contemporary Pro Stocker, have more weight on the front-end than the back. Again, if that doesnt work, then lateral load transfer will not be the right parameter to change. The trend in dirt racing seems to be leaning toward a left side weight percentage of around 53.5 to 55 and somewhere between 75 and 125 pounds of wedge. 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. 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. The same is true in bikes, though only longitudinally.[4]. is the wheelbase, 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. Likewise, accelerating shifts weight to the rear, inducing under-steer, and cornering shifts weight to the opposite side, unloading the inside tires. So a ride height adjustment to your race car, or a roll centre geometry . 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. Understanding lateral weight transfer in racing cars. - LinkedIn When cornering, the sprung mass of the car will roll by an amount , the roll angle. "Right now, none. Weight Transfer: how it works and how to use it in setup 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. Roll is simply the effect of a suspension reacting to weight transfer. The figure only shows forces on the car, not forces on the ground and the CG of the Earth. The initial lurch will sink the car. We now have roll moment arm and roll stiffnesses to play with. h Changing the moment generated by this component requires changes in either the unsprung mass or its CG height. Can you see the trend? Weight transfer has two components: Unsprung Weight Transfer: This is the contribution to weight transfer from the unsprung mass of the car. A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. It is always the case that Lf plus Lr equals G, the weight of the car. is the center of mass height, The secret to answer this question is to focus not on total lateral weight transfer on the car, but instead, on how it is distributed between front and rear tracks. Weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. 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. Effect of downforce on weight transfer during braking Figure 8 clarifies. So lets try it with a 1200 kg vehicle with CG height varying from 100 mm to 1 m (which is ridiculously high even for a road car). [6] They push backwards on the tires, which push on the wheels, which push on the suspension parts, which push on the rest of the car, slowing it down. If , and will have the term inside brackets resulting in . Drag Race Suspension Tuning - RacingJunk News Lets analyse the moment involved in roll. Scott Bloomquist talks lead weight and weight transfer in dirt racing This bias to one pair of tires doing more "work" than the other pair results in a net loss of total available traction. The lateral force of the track is the sum of lateral forces obtained from each tyre. 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 . This component will, however, be altered by changes in other components (e.g. Car Setup Science #3 - Load Transfer - Paradigm Shift Driver Development This is given by: Here, is the sprung weight distribution to the axle being analysed and is the roll centre height for the track. Both of these changes will involve adding, removing or repositioning mass (and therefore parts) within the unsprung part of the car. Its also called the kinematic load transfer component, because the roll centres are defined by the suspension kinematics. With 250-lb/in front springs, the same 1000 pound weight transfer will lift the front end a total of two inches. 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. {\displaystyle \Delta Weight_{front}} 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. The manual of the vehicle used here specified a roll stiffness values ranging from 350,000 Nm/rad to 5,600,000 Nm/rad. Then the expansion of the tire will begin to lift the car. Under heavy or sustained braking, the fronts are . 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. Conversely, under braking, weight transfer toward the front of the car can occur. 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). Please, leave a comment below, to let me know what you liked most in this article or what else you would like to know about the subject, or even some criticism or any knowledge you might want to share. We need to recognise that not all the weight transfer goes via the springs, dampers and anti-roll bars. For example, imagine a vehicle racing down a straight and hitting the brakes. Now lets stop for a moment to analyse the influence of the gravity term on the lateral load transfer component. 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. In my time in Baja, I have done calculations of the type for vehicles that had roughly the same weight distribution and wheelbases of approximately 1500 mm. An exception is during positive acceleration when the engine power is driving two or fewer wheels. 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. Cornering - Lateral load transfer theRACINGLINE.net

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