In automobiles, load transfer is the imaginary "shifting" of weight around a motor vehicle during acceleration (both longitudinal and lateral). This includes braking, or deceleration (which can be viewed as acceleration at a negative rate). Load transfer is a crucial concept in understanding vehicle dynamics.
Often load transfer is misguidedly referred to as weight transfer due to their close relationship. The difference being load transfer is an imaginary shift in weight due to an imbalance of forces, while weight transfer involves the actual movement of the vehicles center of gravity (CoG). Both result in a redistribution of the total vehicle load between the individual tires.
The major forces that accelerate a vehicle occur at the tires contact patch. Since these forces are not directed through the vehicle's CoG, one or more moments are generated. It is these moments that cause variation in the load distributed between the tires. Often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. Although it is interesting to note that a perfectly rigid vehicle without suspension that would not exhibit pitching or rolling of the body would still undergo load transfer. However, the pitching and rolling of the body does result in weight transfer.
Load transfer is undesirable because it negatively affects the total amount of traction available to accelerate a vehicle in any direction. Generally, for a given vehicle load more total traction will be available if the load is shared equally between all the tires, than if any single tire carries more of the load. This tire characteristic is attributed to a phenomenon known as tire load sensitivity .
Lowering the CoG towards the ground is one method of reducing load transfer. As a result load transfer is reduced in both the longitudinal and lateral directions. Another method of reducing load transfer is by increasing the wheel spacings. Increasing the vehicles wheel base (length) reduces longitudinal load transfer. While increasing the vehicles track (width) reduces lateral load transfer. Most high performance automobiles are designed to sit as low as possible and usually have an extended wheel base (length) and track (width).
See also
