First. That due to the inequalities of the road, which produces a torsional twist.
Second. A lateral swing, caused by traveling alongside a hill, or due to centrifugal force when making a turn rapidly.
Third. A fore and aft movement, as when traveling over undulating surfaces, or in suddenly stopping and starting.
Fig. 2a. Half Elliptic.
For these reasons springs must be made to compensate for such motions, and to absorb the jar as much as possible.
Fig. 3. Three-quarter Elliptic.
The Springs.—Many forms of spring mountings have been devised, but the following illustrations show the types which set forth the principles involved. Outside of coiled springs which are used in some forms of delivery cars, the standard springs are leaf springs, built up from a number of steel leaves.
There are four distinct forms of springs used, as follows: