Sprung and Un-sprung Weight
The sprung weight refers to the weight which is supported by the suspension springs. The weight of the vehicle’s body, frame, engine, transmission, interior, fuel, and passengers constitute the sprung weight.
The un-sprung weight refers to the weight which is not supported by the suspension springs i.e. weight of the components between the springs and road surface. The un-sprung weight includes the weight of wheels, axles, steering linkage, and some suspension components. It may be noted that un-sprung weight should be kept as low as possible to achieve pleasant ride.
Oscillation of the Sprung and Un-sprung Weight
Oscillation and jolting of the sprung and un-sprung parts of the vehicle have a particularly gear effect on riding comfort.
The oscillation and jolting can be classified as follows:
● Oscillation of sprung weight
Pitching: Up and down oscillation of the car, at front and rear, in relation to its centre of gravity is called pitching.
Rolling: When turning or when driving on a bumpy road, the springs on one side of the vehicle expand, while those on the other side contract. This results in body rolling in the lateral (side-to-side) direction.
Bouncing: Bouncing in the up and down movement of the auto body as a whole. When a car is running at high speeds on an undulating surface, bouncing is likely to occur. Also, it occurs easily when the springs are soft.
Yawing: Yawing is the movement of the car’s longitudinal centreline to the right and left, in relation to the car’s centre of gravity. On roads where pitching occurs, yawing is also likely to occur.
● Oscillation of Un-sprung Weight
Hopping: Hopping is the up and down bouncing of the wheels which usually occurs on corrugated roads while driving at medium and high speeds.
Tramping: Tramping is the up and down oscillation in opposite directions of the left and right wheels, causing the wheels to skip over the road surface. This occurs more easily in vehicles with rigid axle suspension.
Wind-up: Wind-up is the phenomenon in which the leaf springs attempt to wind themselves around the axle due to the driving torque.
