Some cars have four-wheel steering.
This can be computer controlled or it can be mechanical, through a direct connection between the front and rear steering boxes, or it can be computer-controlled, or the rear wheels can be mounted on special, compliant mounts. As cornering forces are applied to them, they alter the steering angles.
With heavier vehicles, increased use of front-wheel drive, and wider, low-profile tyres, more steering effort is needed, so power assistance is used.
A hydraulic pump is driven from the engine, to provide pressure to help the driver. The power steering system is designed so that even if the engine or the power steering system fails, the vehicle can still be controlled. However, much more driver effort is required.
The relationships between the steering system, the wheel positions, and the suspension system, form what is called the steering geometry. These relationships must always stay within manufacturer specifications.
