1071 Live rigid axle rear suspension

Suspension geometry characteristics of a live axle are as follows:

1 Wheel camber is zero irrespective if the vehicle is stationary or moving round a bend in the road.

2 If one wheel moves over a hump or dip in the road then the axle will tilt causing both wheels to become cambered.

3 Because both wheels are rigidly joined together the wheel track remains constant under all driving conditions.

4 Because the axle casing, half shafts and final drive are directly supported by the wheels, the unsprung weight of a live axle is very high.

5 With a live rigid axle, which is attached to the body by either leaf or coil springs, the body will tilt about some imaginary roll centre roughly mid-way between the upper and lower spring anchorage points.

6 Horizontal fore and aft or lateral body location is achieved by using the leaf springs themselves as restraining members or, in the case of coil springs which can only support the vehicle's vertical load and therefore cannot cope with driving thrust and side loads, horizontally positioned control rods.

Without accurate control of horizontal body movement relative to the axle casing caused by vertical deflection of the springs or longitudinal and transverse forces, the body's weight distribution would be unpredictable which would result in poor road holding and steering response.

Hotchkiss drive suspension (Fig. 10.84(a)) This is the conventional semi-elliptic spring suspension which has each spring positioned longitudinally on each side of the axle and anchored at the front end directly to a spring hanger attached to the body structure and at the rear end indirectly via swing shackle plates to the rear spring hangers, the axle being clamped to the springs somewhere near their mid-span position. Thus fore and aft driving and braking forces are transmitted through the front half of the springs and lateral forces are accommodated by the rigidity of the spring leaves and spring anchorage.

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