TECH > Strut / Swaybars and Bushings  
   

 





 
Strut / Sway Bar and Bushings Basics
There is more to the suspension then your basic upgrades. This is where things get serious!

 

 

Strut Bars:

Strut Bars (Strut Tower Bar) is one of those modifications which will have different effect on every type of vehicle. On the cars with rigid chasis strut bars will make less difference. Also the effect of a strut bar is much more notisable on a track then in grocery-store, every-day type of driving.

When you corner, the whole car's chassis is twisting slightly. In the front (and perhaps at the back, but not so often) the suspension pillars will be moving relative to each other because there's no direct physical link between them. They are connected via the car body, which can flex depending on its stiffness. A strut brace bolts across the top of the engine to the tops of the two suspension posts and makes that direct physical contact. The result is that the whole front suspension setup becomes a lot more rigid and there will be virtually no movement relative to each side. In effect, you're adding the fourth side to the open box created by the subframe and the two suspension pillars.

There are adjustable and solid types of strut bars

 

 

Swaybars (Anti-Roll Bars):

Sometimes referred to as anti-roll bars or stabilizer bars. This is a very popular suspension modification.

Larger sway bars have two main effects. They change the vehicle balance in terms of understeer or oversteer, and increase roll resistance. Both of these attributes can provide increased overall grip.

Most factory vehicles are biased towards understeer, so the fitting of a larger rear sway bar will help in providing a more neutral characteristic in the handling. This is due to the increase in roll stiffness at the rear, which loads the rear wheels more unevenly and provides slightly less grip at the rear than previous. The reason for this is the rear end is resisting more of the roll, the front end resists less in proportion, leaving the front wheels more evenly loaded, therefore more available front end grip, which reduce understeer.

Sway bars are seen as a good method as they typically do not affect ride quality on roads; essentially body roll is the single largest change one can do to help improve the camber curve and increasing the effective spring rate at the wheel (AKA wheel rate) can be done with sway bars.


Typical anti-roll bar (swaybar) kits include the uprated bar, a set of new mounting clamps with polyurethane bushes, rose joints for the ends which connect to the suspension components, and all the bolts etc that will be needed.

As you may have read at the top of the page, it is very important to reduce your unsprung weight in order for the suspension to carry less load and to react faster. The two major styles of sway bars are solid and hollow. The major differences between the two are weight and strength. Hollow sways bars weigh less than solid and solid sway bars are stronger. Both of these points can be argued though, depending on the manufacturer and end users’ experiences. In general though, either would be a fine choice with no real clear cut favorite.

Lastly, it is worth mentioning that a swaybar can be adjustable. As you can see on the above, middle image, there are 3 mounting points on the end of that swaybar. Adjustable swaybars will allow you to choose how tightly a swaybar would perform and how much roll it will allow in the corner. It will also affect how much the car oversteers or understeers and will allow you to dial in your suspension setup much more precisely.

 

 

End Links:

Sometimes referred to as drop links. This is a very popular suspension modification.

In order to discuss the function of end links, one has to consider how they work in conjunction with a sway bar. The entire purpose of a sway bar is to act as a torsion spring. In order to do this you need some way to twist it. That twisting ability is provided by a bent "lever" at each end of the bar and allowing that lever to be pushed and pulled by attaching it to a suspension component that moves up and down.

Also, the stock rear links are made from plastic. The OEM unit flexes quite easily, even under minor loads.

Aftermarket rear end links help solve this problem: some feature a length that is shorter than the stock links to solve the fuel filler neck problem, and they are considerably stiffer than the stock links. Made with bodies that are water jet cut from aluminum, extruded aluminum, or CNC manufactured, they are incredibly stiff when compared to the stock pieces. This stiffness in turn allows the motion from the suspension to be applied to the swaybar. This allows the sway bar to operate to its full potential, and apply forces where necessary.

 

 

Bushings:

 

These are the rubber grommets which separate most of the parts of your suspension from each other. They're used at the link of an A-Arm with the subframe. They're used on anti-roll bar links and mountings. They're used all over the place, and from the factory, I can almost guarantee they're made of rubber. Rubber doesn't last. It perishes in the cold and splits in the heat. Perished, split rubber was what brought the Challenger space shuttle down. This is one of those little parts which hardly anyone pays any attention to, but it's vitally important for your car's handling, as well as your own safety, that these little things are in good condition. My advice? Replace them with polyurethane or polygraphite bushes - they are hard-wearing and last a heck of a lot longer.

Rubber works very well as a noise and vibration dampener as it can actually seem to absorb energy although ultimately it does convert kinetic energy to heat. Polyurethane, on the other hand, needs to move in another direction to accept the load. It too will heat up, but it will work much more effectively as a bearing surface than rubber. Rubber perishes over time and will break down if contaminated with chemicals like grease and oil. Polyurethane on the other hand is relatively impervious to chemicals.

When it comes to the performance aspect of bushings swap, some cars (ex. older Lexus) need the new bushings as a #1 upgrade. Keep in mind that it is a very economically priced upgrade that noticeably improves handling. You may not want a set of sway bars once you replace your busings from rubber to a more dense polyurethane.

Like all suspension-related items though, bushings are a tradeoff between performance and comfort. The harder the bush compound, the less comfort in the cabin. While you may love the feeling of swapping out 20 OEM rubber bushings, your wife and her scrapbook club members may have another opinion!

 

Sources:
Suspension bible
Unabomber @ NASIOC Forums