Weight transfer and load transfer are two expressions used somewhat confusingly to describe two distinct effects in the context of automobile and motorcycle dynamics:
the change in load borne by different wheels of even perfectly rigid vehicles during acceleration the change in center of mass (CoM) location relative to the wheels because of suspension compliance or cargo shifting or sloshing In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. This would be more properly referred to as load transfer, and that is the expression used in the motorcycle industry, while weight transfer on motorcycles, to a lesser extent on automobiles, and cargo movement on either is due to a change in the CoM location relative to the wheels. This article uses this latter pair of definitions.
Load transfer In wheeled vehicles, load transfer is the measurable change of load borne by different wheels during acceleration (both longitudinal and lateral). This includes braking, and deceleration (which is an acceleration at a negative rate). 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. Load transfer is a crucial concept in understanding vehicle dynamics. The same is true in bikes, though only longitudinally.
Cause
The major forces that accelerate a vehicle occur at the tires' contact patches. 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. 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. A perfectly rigid vehicle, without suspension that would not exhibit pitching or rolling of the body, still undergoes load transfer. 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. contact patch displacement relative to wheel. Lowering the CoM 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 vehicle's wheelbase (length) reduces longitudinal load transfer while increasing the vehicle's track (width) reduces lateral load transfer. Most high performance automobiles are designed to sit as low as possible and usually have an extended wheelbase and track. 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":
Δ W e i g h t f r o n t = a h b m {\displaystyle \Delta \mathrm {Weight} _{\mathrm {front} }=a{\frac {h}{b}}m} or Δ W e i g h t f r o n t = a g h b w {\displaystyle \Delta \mathrm {Weight} _{\mathrm {front} }={\frac {a}{g}}{\frac {h}{b}}w}
where Δ W e i g h t f r o n t {\displaystyle \Delta \mathrm {Weight} _{\mathrm {front} }} is the change in load borne by the front wheels, a {\displaystyle a} is the longitudinal acceleration, g {\displaystyle g} is the acceleration of gravity, h {\displaystyle h} is the center of mass height, b {\displaystyle b} is the wheelbase, m {\displaystyle m} is the total vehicle mass, and w {\displaystyle w} is the total vehicle weight. 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.
Center of mass
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