Ask Joe Mechanic: Steering and Suspensions Part 2

This week we will continue the discussion of steering systems and then get into the basics

of suspensions. Last week we discussed the common types of steering, recirculating ball and rack and pinion. A system that has been tried by a number of manufacturers in recent years is four-wheel steering. There are two types, active and passive.

            In active four-wheel steering, there is a set of steering linkages connected to the rear wheels similar to what is used in the front. Most rear steering is electronically controlled with a system of sensors and actuators. In most types, the rear wheels will turn differently dependant on speed. At low speed, such as for parking, the rear wheels will steer opposite what the front wheels do to reduce the turning radius required. Meanwhile, at higher speeds, such as during highway driving, the electronic controls will turn the wheels in the same direction as the front wheels, which will increase directional stability. General Motors offered a system of this type on Chevy and GMC trucks and Tahoes. However, the response was limited, with only about 16,500 vehicles being sold in the three years it was offered so they discontinued it in 2005. It is offered now mostly by higher end brands like BMW, Infinity, Porsche, Lexus and some Mazdas.

            Passive four-wheel steering is a more commonly seen system, and on many cars, you are not even aware that it is there. Basically, through the design of linkages and bushings, the lateral forces generated during turning at higher speeds will turn the rear wheels slightly inward to increase the directional stability of the vehicle.

            One other very important feature of the steering system is the collapsible steering column. This feature was originally introduced by Mercedes in 1959 and was adopted by the American automakers during the 1960s after extensive lobbying by Ralph Nader. This was much more important with the recirculating ball steering systems where the steering box was mounted forward on the frame.  However, even with the firewall mounted rack and pinion systems of most cars, it is still an important safety feature that most people do not even think about.

            In the next post we will start to explore suspensions and the different types of systems and how they work. We will also examine some of the calculations that go into determining how a system is designed.

Elements of this post have been sourced from www.wikipedia.org.