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. Lets say that you are a race engineer and your driver is having trouble to go around the slowest corners on the circuit. Slamming through your gears while mashing on the gas pedal is one way to do it, and an extremely satisfying way to jump off the line just for kicks, but it isn't necessarily the best way to extract all the performance from your car as you possibly can. 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. Again, if that doesnt work, then lateral load transfer will not be the right parameter to change. Performance Engineer, withexperience in IMSA LMP2, Porsche Cup Brazil and othercategories. Figure 10 shows the plot of the roll angle component versus gravity term. This article explains the physics of weight transfer. contact patch displacement relative to wheel. The reason I'm asking you is because you're one of the bigger guys in the pit area. Learning to do it consistently and automatically is one essential part of becoming a truly good driver. 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. Load transfer is a crucial concept in understanding vehicle dynamics. is the center of mass height, This analysis may even be used to prepare tyre data, in order to make the bicycle model more realistic. We dont often notice the forces that the ground exerts on objects because they are so ordinary, but they are at the essence of car dynamics. : 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. Antiroll bars are generally added to the car to make it stiffer in roll without altering the ride characteristics. See you soon! Bear in mind that lateral load transfer affects the balance through tyre load sensitivity (the tendency of the tyres to generate higher lateral forces at a decreasing rate with higher vertical loads). 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. 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 happens because raising the roll centre in any axle will approximate the roll axis to the sprung weight CG. 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. 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. Front lateral load transfer is not necessarily equal to the load transfer in the rear side, since the parameters of track, weight and height of the CG are generally different. 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. Refer again to figure 1. Likewise, accelerating shifts weight to the rear, inducing under-steer, and cornering shifts weight to the opposite side, unloading the inside tires. At this moment, you should be convinced of the irrelevance of the gravity term on roll angle weight transfer component. Our system is proven to increase traction, and reduce fuel consumption and track maintenance. For the trailer, the chain pulls down . The vehicle mass resists the acceleration with a force acting at its center of gravity. Balancing a car is controlling weight transfer using throttle, brakes, and steering. In this analysis, we will be interested in lateral load transfer in a single axle, and I will discuss the three mechanisms by which that happens, namely, roll resistance moment from springs and antiroll bars, direct lateral force load transfer and lateral load transfer from unsprung mass. This component will, however, be altered by changes in other components (e.g. Conversely, under braking, weight transfer toward the front of the car can occur. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn can occur. Weight transfer is an advanced techniqe which can impact the cart in four directions: front, back, and then each side of the kart. Now lets stop for a moment to analyse the influence of the gravity term on the lateral load transfer component. 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. 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. Also, if you liked this post, please share it on Twitter or Facebook, and among your friends. Here, the load transfer is increased by means of the lateral load transfer parameter, instead of the FLT. Even purpose-built cars, like a contemporary Pro Stocker, have more weight on the front-end than the back. If our car is a little loose going into the turns we may raise all the weight 6 or 8 inches. Braking causes Lf to be greater than Lr. Calculating the load transfer in a vehicle is fairly straightforward. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. When a body rolls, the motion generates rotational torque which must be overcome every time we want to change direction. Now that we know the best ways to change roll stiffness, lets see how it affects lateral load transfer. The lateral force of the track is the sum of lateral forces obtained from each tyre. Weight transfer of sprung mass through suspension links, The second term is the weight transfer of the body through the suspension links, Weight transfer of sprung mass through springs, dampers, anti-roll bars. Hence, springs and tyre pressures should only be changed when other aspects need modification, but not only roll stiffness itself (unless the vehicle has no antiroll bar). A. 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. Postby BillyShope Wed Aug 22, 2007 5:48 am. Lowering the CoM towards the ground is one method of reducing load transfer. Then, a series of steer angles in the range of interest is selected. 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. 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. Figure 13 shows the contour plots of lateral weight transfer sensitivity as a function of front and rear roll stiffnesses. That rationale comes from simple physics. 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. It applies for all cars, especially racing, sports and high performance road cars. Steering. Notice that this conclusion doesnt necessarily hold true for different roll axis inclinations. It is the process of shifting your body weight from one side of the kart to the other or leaning forward or back. So far, we have discussed the influence of each component in lateral load transfer in isolation. For example, imagine a vehicle racing down a straight and hitting the brakes. 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. The manual of the vehicle used here specified a roll stiffness values ranging from 350,000 Nm/rad to 5,600,000 Nm/rad. Just as taking Claritin or Benadryl reduces your symptoms without curing your allergies, reducing roll reduces the symptoms but does not appreciably cure weight transfer. Weight transfer occurs as the vehicle's CoM shifts during automotive maneuvers. 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. a Hence: This is the total lateral load transfer on the car. The "rate of weight transfer" is considered important. 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. Bear in mind that the roll moment arm is the perpendicular distance between the CG of the sprung mass and the roll axis. The moment can be divided by the axle track to yield a lateral load transfer component: Where is the unsprung weight on the track being analysed. Figure 12 shows a finite element stress analysis, with colours closer to yellow and green indicating higher stresses. Lets now analyse roll stiffnesses. This curve is called the cornering coefficient curve for the track. When the driver gets on the brakes, the total remains the same . Its not possible to conclude directly what influence increasing roll centre heights will have. Vertical load is the load actually seen at the tire contact patch. In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. The figure shows a car and the forces on it during a one g braking maneuver. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each. Literally, the ground pushes up harder on the front tires during braking to try to keep the car from tipping forward. You must learn how different maneuvers . 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. Usually, I'll have 50-80 lbs," Bloomquist told RacingNews.co from Lucas Oil Speedway a few weeks back. Same theory applies: moving the right rear in will add more static right rear weight and will cause more weight transfer. Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. The lateral load transfer parameter. This is the weight of the car; weight is just another word for the force of gravity. The second law: When a force is applied to a car, the change in motion is proportional to the force divided by the mass of the car. These effects are good for tightening up the car when winged down, but opposite for roll right. o 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. Total lateral weight transfer is a combination of 3 distinct effects: Lateral force generated by the unsprung mass of the suspension and lateral acceleration is reacted directly by the tires, giving rise to a vertical component defined as Fz1. 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. The front wheels must steer, and possibly also drive. The loads in each wheel determine the vehicles maximum cornering, braking and acceleration capability, then the lateral weight transfer is a key factor in a racing car performance. The vehicle's weight is transferred forwards and the front suspension compresses: 'compression'. This fact can be explained at deeper levels, but such an explanation would take us too far off the subject of weight transfer. Figure 14 can lead us to very interesting conclusions. 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. Naturally, you're more inclined to wheelstand with an increase in acceleration. 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. If that is the case in the front axle, the car will understeer, if it is in the rear axle, it will oversteer. The overall effect will depend upon roll centre heights and roll stiffnesses, and a definitive conclusion will require a deeper analysis. Why? This is given by: Here, is the sprung weight distribution to the axle being analysed and is the roll centre height for the track. {\displaystyle \Delta Weight_{front}} 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. If your driver complies about oversteer in the slowest corners, it means that the front axle is generating higher lateral force than the rear. 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. This can be done in multiple ways. This leads some to think that increasing roll centre heights will actually decrease weight transfer because it reduces roll. For this case, roll moment arm decrease with roll centre heights was smaller than the increase in roll centre heights themselves. 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. The simplest component of load transfer is the one related to 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. That is a lot of force from those four tire contact patches. 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. Weight Transfer - A Core of Vehicle Dynamics. 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. It can be varied simply by raising or lowering the roll centre relative to the ground.
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