Suspensions can be divided into the following two types according to their structures.
(1) Rigid axle suspensions Both wheels are supported by an axle housing or axle beam. Therefore, the left and right wheels move together. The characteristics of rigid axle suspensions are:
- The number of parts is small and the construction is simple. Therefore, maintenance is easy.
- It is durable enough for heavy-duty use.
- When turning, there is little tilting of the body.
- There is little change in the alignment due to the up-and-down movements of the wheels. Therefore, there is less tire wear.
- Since the unsprung weight is great, riding comfort is poor.
- Since the movement of the left and right wheels mutually influence one another, vibration and oscillation occur rather easily.
(2) Independent suspensions Each wheel is supported by an independent arm, which is mounted to the vehicle body. Therefore, the left and right wheels move independently. The characteristics of independent suspensions are:
- The unsprung weight is low and riding comfort is good.
- The springs have nothing to do with the positioning of the wheels, so softer springs can be used.
- Since there is no axle connecting the left and right wheels, the floor and engine mounting position can be lowered. This means that the vehicle’s center of gravity will be lower.
- The construction is rather complex.
- Tread and alignment change with the up-and-down motions of the wheels.
- Numerous models are equipped with a stabilizer bar to reduce rolling during cornering and improve the comfortability to ride.
There are various types of rigid axle suspension. This section explains the rigid axle suspension types currently used in Toyota vehicles and their characteristics.
(1) Trailing arm type with torsion beam This type is mainly used in the rear suspension of front-engine front-wheel drive (FF) vehicles, and employs a structure consisting of a suspension arm and stabilizer bar welded to a twistable axle beam (There are some models with no stabilizer bar.). Due to its simple structure and compact size, unsprung weight can be reduced for a better ride. In addition, it also enables the securing of a large luggage space. When rolling occurs such as during cornering and on rough roads, the stabilizer bar twists with the axle beam. As a result, rolling is reduced due to the action of the stabilizer bar, thereby maintaining vehicle stability. When jacking up the vehicle, do not lift the torsion beam section with a jack or the like.
(2) Parallel leaf spring type This type of suspension is used for the front suspension of trucks and buses, etc., and for the rear suspension in commercial vehicles. Characteristics:
- Construction of the suspension is simple but comparatively strong.
- Difficult to use a very soft spring, therefore riding comfort is not very good. (3) Leading/trailing arm type with lateral rod This type of suspension is used for the front and rear suspensions of the Land Cruiser, or trucks, etc. Characteristics:
- Riding comfort is good.
- Rigidity is high. (4) 4-link type This type is used for the rear suspension. It provides the best riding comfort of all the rigid-axle suspensions.