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). 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 . The only reason a car in neutral will not coast forever is that friction, an external force, gradually slows the car down. Understanding weight transfer is a fundamental skill that racecar drivers need to know. 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. 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. The "rate of weight transfer" is considered important. Transition This is the point at which the car 'takes its set'. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. The second term can be changed modifying the suspension geometry, usually difficult or not allowed in some competitions. How can weight shift when everything is in the car bolted in and strapped down? 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. More wing speed means we need to keep the right rear in further to get the car tighter. 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). Ideally, this produces 0.5, or 50-percent, to show that the right front/left rear sum is equal to the left front/right rear sum. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright . This component will, however, be altered by changes in other components (e.g. The same is true in bikes, though only longitudinally.[4]. "The ride height is meant to be in one spot you should look to move weight, adjust the shocks . Figure 6 shows the CAD design of a similar gearbox, highlighting the different options for installing pickup points. 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. As long as the tires stay on the car, the ground pushing on them slows the car down. Then, most of the solutions available will be related to the subject of this post: lateral load transfer. 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. We'll assume the car's side to side weight distribution is equal. 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 When a car leaves the starting line, acceleration forces create load transfer from the front to the rear. Weight Transfer - A Core of Vehicle Dynamics. How much lead weight do you have on your car? Tire Offsets. 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. What happened here? Literally, the rear end gets light, as one often hears racers say. We derived the equations of lateral load transfer in one axle of the car, showing that its composed of three components: Unsprung weight component not useful as a setup tool because of the effect that it has on ride, specifically wheel hop mode. When the driver gets on the brakes, the total remains the same . It is what helps us go fast! Because of this interaction with the springs, this component is also referred as the elastic weight transfer component. 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. NOTE: This information is from an NHRA Rule Book 2019 Addendum. {\displaystyle g} The added axle weight will slow the release of the stretch in the tire and help hold traction longer. Queens GTO/Viper. If you have no suspension (ex. Lets now analyse roll stiffnesses. These adjustable bars generally have blade lever arms, as the one shown in figure 11. Lets now see how these components affect each other and how they affect load transfer together. 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 %. The net loss can be attributed to the phenomenon known as tire load sensitivity. 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. 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. When you increase roll centre height in one axle you increase the overall lateral load transfer on that axle, while decreasing it on the opposite axle. Term 2 always leads Term 3. For setup, we look into changing the lateral load transfer in one axle relative to the other, to affect balance. On limit conditions, this will translate in one of the axles breaking loose and skidding before the other. The softer the spring rate the more weight transfer you will see. The more the body rolls and the faster the body rolls, the more rotational . 35% Front 420 lbs 780 lbs 280 lbs 520 lbs LH Turn - New Stiffer Front Roll Bar 33.3% Do you see how small it is compared to the roll stiffness of the car? Figure 14 shows the contour plot. The front wheels must steer, and possibly also drive. 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. 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 happens because raising the roll centre in any axle will approximate the roll axis to the sprung weight CG. 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. {\displaystyle m} The car should be at minimum weight, using ballast as needed to make the proper weight. 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. When the car moves in one of these directions, the car's weight moves in the opposite direction and compresses the suspension in this area. Front roll stiffness distribution only modifies Term 3 and hence increasing front roll stiffness always increases understeer. The driver is said to manage or control the weight transfer. 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? By analysing Figure 9 you can see that lateral load transfer is very sensitive to changes in roll centre height. The term is a gravity component that arises due to the sprung CG being shifted to the side when the chassis rolls. is the change in load borne by the front wheels, The actual wheel loads are calculated for a series of FLT, which can go from 0 to 1.0, for the given track load. After that, we will see how the components of load transfer can be manipulated to tune the balance of the car. Then, a series of steer angles in the range of interest is selected. The weight distribution on the rear axle was 54 %. Before I explain this, let me talk about a good thing to understand the subject the steady-state analysis of a pair of tyres. The distribution of dynamic loads can be altered with aerodynamics, with the regulation of wings or the static/dynamic height of the vehicle. The lateral load transfer parameter. It can be varied simply by raising or lowering the roll centre relative to the ground. Acceleration causes the sprung mass to rotate about a geometric axis resulting in relocation of the CoM. 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. 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. 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 . This article uses this latter pair of definitions. Increasing the vehicle's wheelbase (length) reduces longitudinal load transfer while increasing the vehicle's track (width) reduces lateral load transfer. 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. FROM LAP TIME SIMULATION TO DRIVER-IN-THE-LOOP: A SIMPLE INTRODUCTION TO SIMULATION IN RACING. 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. I hope this article was useful to you, and that you have enjoyed reading it. 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. Can you see the trend? Lets say the car is rear wheel drive with a rear weight distribution and large, lightly loaded tyres. Well, a thousand changes to the car could be applied. Then, the total lateral weight transfer is therefore a sum of the three parts: The first term is usually small in comparison, and it is also difficult to modify, and is therefore, sometimes ignored. 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. The total lateral load transfer on the car can be calculated from its free body diagram, as shown in figure 1. Since these forces are not directed through the vehicle's CoM, one or more moments are generated whose forces are the tires' traction forces at pavement level, the other one (equal but opposed) is the mass inertia located at the CoM and the moment arm is the distance from pavement surface to CoM. h 500 - 1500 (400 - 1,100) The suspension roll stiffness calculation for K9 was in the order of 4,500 ft-lb/degree of roll. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each. A. In conclusion, it was a huge effort by Tin . 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. It is these moments that cause variation in the load distributed between the tires. Inside percentages are the same front and rear. It arises from the force coupling effect that roll centres have, directly linking forces on sprung mass to the unsprung mass. o G cannot be doing it since it passes right through the center of gravity. The front and rear roll centres heights were kept equal, but varied from 3 mm to the CG height (254 mm). The braking forces are indirectly slowing down the car by pushing at ground level, while the inertia of the car is trying to keep it moving forward as a unit at the CG level. Weight transfer is one parameter that is minimized - to aim for even loading on all four tires; resulting in maximum grip during cornering. No motion of the center of mass relative to the wheels is necessary, and so load transfer may be experienced by vehicles with no suspension at all. 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. It applies for all cars, especially racing, sports and high performance road cars. In figure 3 the effect is repeated, but from a different perspective. t So far, we have discussed the influence of each component in lateral load transfer in isolation. Here they are the real heavyweights! The analysis procedure is as follows: The potential diagram is a benchmarking of the performance that can be achieved by a pair of tyres. This law is expressed by the famous equation F = ma, where F is a force, m is the mass of the car, and a is the acceleration, or change in motion, of the car. Braking causes Lf to be greater than Lr. Hence: This is the total lateral load transfer on the car. Our system is proven to increase traction, and reduce fuel consumption and track maintenance. The forces upon the springs are reacted by the tyres, and that contributes to lateral load transfer. 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.

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