In automobiles, weight transfer (often confused with load transfer) referrers to the redistribution of weight supported by each tire during acceleration (both longitudinal and lateral). This includes braking, or deceleration (which can be viewed as acceleration at a negative rate). Weight transfer is a crucial concept in understanding vehicle dynamics.
Weight transfer occurs as the vehicles center of gravity (CoG) shifts during automotive maneuvers. Acceleration causes the sprung mass to rotate about a geometric axis resulting in relocation of the CoG. Liquids such as fuel readily flow within their containers also causing changes in the total vehicles CoG. Further more as fuel is consumed not only does the position of the CoG change the total weight of the vehicle is reduced.
By way of example, when a car accelerates, a weight transfer toward the rear wheels is said to occur. An outside observer can witness this as the car visibly leans to the back, or "squats". Conversely, under braking, weight transfer toward the front of the car will occur. Under hard braking it is clearly visible even from inside the car as the nose "dives" toward the ground. Similarly, during changes in direction (lateral acceleration), weight transfer to the outside of the direction of the turn occurs.
Weight transfer causes the available traction at all four wheels to vary as the car brakes, accelerates, or turns. For example, because of the forward weight transfer under braking, the front wheels do most of the braking. This bias to one pair of tires doing more ‘work’ than the other pair results in a net loss of total available traction. The net loss can be attributed to the phenomenon known as tire load sensitivity .
An exception is during positive acceleration when the engine power is driving two or less wheels. In this situation where all the tires are not being utilized weight transfer can be advantages. As such, the most powerful cars are never front wheel drive, as the acceleration in itself causes the front wheels' traction to decrease. This is why sports cars always 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).
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