Steering

Automobiles are steered by a system of gears and linkages that transmit the motion of the steering wheel to the pivoted front wheel hubs. The gear mechanism, located at the lower end of the shaft carrying the steering wheel, is usually a worm-and-nut or cam-and-lever combination that rotates a shaft with an attached crank arm through a small angle as a steering wheel is turned. Tie rods attached to the arm convey its motion to the wheels. In concerning, the inner wheel must turn through a slightly greater angle than the outer wheel, because the inner wheel negotiates a sharper turn. The geometry of the linkage is designate to provide for this.

When the front wheels are independently suspended, the steering must be designed so that the wheels are not turned as tie-roads lengthen and shorten as result of spring action. The point of linkage attachment to the steering gear must be placed so that it can move vertically with respect to the wheel mountings without turning the wheels.

The distribution of weight between the front and rear wheels of automobiles shifted toward the front as the engine and passenger compartment were moved forward to improve riding comfort and road-handling characteristics. As the weight carried on the front wheels increased to more than the half of the total vehicle weight, the effort necessary to turn the wheels in steering increased. Larger, heavier cars with wider tires and lower tire pressure also contribute to drag between tire and road that must overcome in steering, particularly in parking. It was originally considered satisfactory to limit the pull on the rim of the steering wheel to 30 pounds (14 kilograms), but this limit proved to be too high. Considerable reduction in the work of steering resulted from increased efficiency of the steering wheel was accomplished by increasing the overall steering gear ratio. Large steering gear ratios make high-speed maneuverability more difficult, however, because the steering wheel must be turned through greater angles. On the other hand, steering mechanisms of higher efficiency are also more reversible; that is, road shocks are transmitted more completely from the wheels and must be overcome to a greater extend by the driver. This causes a dangerous situation on rough roads or when a front tire blows out, because the wheel may be jerked from the driver's hands.

Wheeled vehicles

After the early efforts to domesticate animals for their burden-carrying abilities, the most significant addition to human locomotion was the wheeled vehicle. It was one of the great inventions of all times because of the contribution that the wheel, and its utilization in a vehicle, makes up applying supplemental sources of power to an individual's mobility. Horses and camels can travel faster than the humans on their backs, but to transport more than one person with a single animal – something most horses had the strength to do – vehicle was needed. Probably the first conveyance of this sort was a plank or log dragged along the ground; the Plains Indians of North America used such a travois of two poles in their transhuman wandering until the 19^th century. Its mechanical inefficiency must have prompted the search for improvements. The invention of the wheel made the contribution of a horse more productive. The power provided by any one horse has grown with changes in vehicles, in harnessing and in the surface on which it operates.

Much of human history saw no technology superior to the sling or travois but when the wheel was devised changes was both substantial and probably fairly rapid. It seems that there were versions of the travois shaped like a platform, with a great reduction in the extent of actual contact with the ground; only the ends of the poles supporting the platform dragged along the surface, where friction would be great. Improvement came with placing a revolving wheel at the end of each of the drag poles. From this advance it was but a minor step to arrive at a two-wheel cart.