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Then, a series of steer angles in the range of interest is selected. 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. Notice the smaller cornering potential for higher values of the lateral load transfer parameter. A larger force causes quicker changes in motion, and a heavier car reacts more slowly to forces. Deceleration Weight Transfer The opposite of the acceleration weight transfer takes place during deceleration. This analysis may even be used to prepare tyre data, in order to make the bicycle model more realistic. . Weight transfer issue | Bob's 4 Cycle Karting The previous weight of the car amounted to 2,425 pounds, while now it is about 2,335 pounds. MichaelP. 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. If you compare figures 13 and 8, you will see that, while lateral weight transfer changes with roll centre heights along contours defined by lines that have the same inclination, the effect is different with respect to roll stiffnesses, as the lines that limit the contours have different inclinations. 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. 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. 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. Why? 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. Roll Stiffness & Weight Transfer - Balance Motorsport It must be reminded that changing this term will only change a part of the total lateral weight transfer. Changing the moment generated by this component requires changes in either the unsprung mass or its CG height. {\displaystyle g} 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. 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. Read more Insert your e-mail here to receive free updates from this blog! Balancing a car is controlling weight transfer using throttle, brakes, and steering. Suspension Geometry - Balance Motorsport The change in this arm with roll centre heights will depend on the wheelbase and weight distribution. 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. Your shock absorbers are considered after your ride and roll stiffness have been selected. 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. Now you know why weight transfer happens. C. Despite increasing the steering angle, the car has taken a line which is not tight enough to take the turn. Conversely, a supercar is built to approximate race geometry with few concessions to prevent spilling the drinks. As with most race car parts, you get what you pay for. 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). Roll is simply the effect of a suspension reacting to weight transfer. The Physics Of Racing Part 1: Weight Transfer | ABRS G cannot be doing it since it passes right through the center of gravity. Our system is proven to increase traction, and reduce fuel consumption and track maintenance. A more in-depth discussion on how each of these moments are generated will now be presented. 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. Do you see where this heading? This button displays the currently selected search type. With those values, the gravity term will be 1662.1 Nm. Here, is the lateral acceleration in G units, is the weight of the car, is the CG height, is the track width and and are the vertical loads on the left and right tyres, respectively. Race Car Ride Height 101- With Jerry Bickel And Chassis - Dragzine Tire Offsets. An outside observer might witness this as the vehicle visibly leans to the back, or squats. Explained: Weight transfer vs body roll (part 2) Same theory applies: moving the right rear in will add more static right rear weight and will cause more weight transfer. 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. What we can do is only influence which portion of the total lateral . 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. contact patch displacement relative to wheel. Transient lateral load transfer is an important aspect of vehicle setup, but lets leave the discussion on that for another day. Refer again to figure 1. 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). 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. He won the Formula Pacific Tasman Championship, won at Silverstone against Ayrton Senna and Martin Brundle in perhaps the greatest year ever in British Formula 3, and qualified for nine starts in F1, a record bettered among his countrymen only by Gilles and Jacques Villeneuve. Before I explain this, let me talk about a good thing to understand the subject the steady-state analysis of a pair of tyres. This can be confirmed by adopting the conclusions from the analysis of figure 10, where we agreed that the gravity term is negligible for roll angle lateral weight transfer component. But these forces are acting at ground level, not at the level of the CG. 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. The actual wheel loads are calculated for a series of FLT, which can go from 0 to 1.0, for the given track load. 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. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. A. If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. 3. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. Understanding Chassis Setup! - Redline Motorsports 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). As fuel is consumed, not only does the position of the CoM change, but the total weight of the vehicle is also reduced. 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. 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. 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 Conversely, if you increase rear roll centre height, lateral load transfer increases on the rear axle and decreases on the front axle. 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. Then the expansion of the tire will begin to lift the car. Car weight distribution: understanding its effects when driving on W Figure 3 shows the plot. The simplest component of load transfer is the one related to unsprung mass. We can split the inertial force into sprung and unsprung components and we will have the following relation: Where is the moment acting upon the sprung mass and is the moment on the unsprung mass. [6] This can be done in multiple ways. Usually, I'll have 50-80 lbs," Bloomquist told RacingNews.co from Lucas Oil Speedway a few weeks back. 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. 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. This bias to one pair of tires doing more "work" than the other pair results in a net loss of total available traction. 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. With 250-lb/in front springs, the same 1000 pound weight transfer will lift the front end a total of two inches. This is generally not the first option to take because of the effect that it has on other aspects of the car. Now that we know the best ways to change roll stiffness, lets see how it affects lateral load transfer. The more the body rolls and the faster the body rolls, the more rotational . The softer the spring rate the more weight transfer you will see. Lesser the Second: Accelerating the car will weight the rear wheels heavily, the front wheels lightly. Sprung weight distribution is calculated as the ratio between the distance from the sprung weight CG to the axle opposite to the one being analysed, , and the wheelbase of the vehicle , times the sprung weight . When a car leaves the starting line, acceleration forces create load transfer from the front to the rear. 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. As we move up to higher categories, the engineering gets more complex. This force is then divided by the weight on the axle, This lateral acceleration is plotted against FLT, with reference steer angle as a parameter. Here, the load transfer is increased by means of the lateral load transfer parameter, instead of the FLT. 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 weight distribution on the rear axle was 54 %. The difference in height between the roll center and center of gravity of the sprung mass gives rise to a moment. For example, if our car had a center of gravity 1 foot above the ground and the tires were 4 feet apart, we would divide 1 foot . 1. 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. 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. Lets analyse the moment involved in roll. {\displaystyle \Delta Weight_{front}} I have heard of many cars running well outside of these parameters and winning. 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. 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. o Liquids, such as fuel, readily flow within their containers, causing changes in the vehicle's CoM. Lets now analyse roll stiffnesses. For this analysis, only the rear axle was considered. How to Make a Winning Race Car Setup - Racing Car Dynamics After that, we will see how the components of load transfer can be manipulated to tune the balance of the car. 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. 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. Figure 1 . This is balanced by the stiffness of the elastic elements and anti-roll bars of the suspension. 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). Bickel explains how the way the 4-link plays into how you adjust the car. This will have a net effect of decreasing the lateral force generated by an axle when the load transfer on it increases. 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. Those of you with science or engineering backgrounds may enjoy deriving these equations for yourselves. The stiffnesses are shown in kgfm/degree, that have clearer meaning, but the data were input in Nm/rad. Weight transfer - Wikipedia Weight . Learning to optimize weight transfer allows us to optimize the grip of the racecar. 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 .