Suspension 101

A crash course from our technical expert
by Ferman Lao | Mar 24, 2010

Hi, Ferman.

Can you discuss the different types of suspension and their advantages under different driving condition and which better for specific type of vehicle?

Gerald

Hi, Gerald.

I\'m assuming that you\'re asking about the differences between modern independent suspension geometries.

The primary function of a suspension is to isolate the occupants as much as possible from poor road conditions while providing better road-holding and control versus a vehicle without a suspension. As you probably know that most modern passenger vehicles will be equipped with independent suspensions which allow each individual wheel to move(on the vertical axis) separately from the other wheels. Examples of the common types of independent suspensions are the Macpherson strut, wishbone, multi-link and trailing arms.

Common front suspension designs will either use a Macpherson strut or double wishbones. Macpherson struts are easier to manufacture, more compact, and they allow for easy setting of the suspension geometry but they aren\'t as precise as double wishbone suspensions. Despite the disadvantage, Macpherson struts are used in a large variety of cars including BMWs, Toyotas, Mitsubishis and, more recently, Hondas.

Double wishbones--while providing much better suspension geometry control-- unfortunately require more space and are more costly to manufacture. Until recently, most, if not all, Hondas used this type of suspension on their front end.

Multi-link suspensions are usually found on rear suspensions and allow for a great degree of suspension geometry control--much better, in fact, than even double wishbones. With precision comes complexity, however, and tuning it requires extensive work. Needless to say, it is also costlier than a double wishbone to properly design and manufacture.

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All the different types of independent suspensions contrast with the early dependent-type suspensions wherein both wheels are tied together. This of course results in one wheel\'s movement influencing the movement of the opposite wheel on the axle pair. For example a negative camber change on the right wheel will result in a positive camber change on the left wheel and vice versa. These are normally tied together with a live axle or a beam axle which hold the wheels on the axle pair parallel to each other. This system is cheap to make and are no longer found on modern passenger cars, however they can still be found on large vehicles such as cargo trucks.

Another type is the semi-independent suspension, which allow the movement similar to independent suspensions but each side affects its axle pair wheel. A good example of this type of suspension is the twist beam rear suspension commonly found on sub compact cars. This design offers a good degree of compactness, simplicity and allows for the deletion of the rear sway or stabilizer bar.

This is of course just a very short overview as suspension design and geometries are not as simple as they sound since with proper tuning, similar performance can be had regardless of which type is under your car. For sport or high-performance driving you only have to look at what\'s on F1 cars to know what\'s the best.

Best regards,

Ferman Lao

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