Interesting sway bar article from UK.

[X5girl]

I was browsing some other BMW forums and found this on the X5.

ADJUSTABLE ANTI-ROLL BAR DROP LINKS.

Why would you need adjustable length anti-roll bar drop-links? Well, for the vast majority of road cars they are not necessary but when you get into the realms of sports suspension tuning then adjustable length drop-links allow the correct pre-loading of the roll bars.

Most people believe the adjustability of the link rods is used to alter the actual roll stiffness of the bar but this is not correct. The adjustable length allows the owner to correctly pre-load the roll bar for neutral roll transition in both left and right turns.

To explain this neutrality, lets assume we have a brand new, perfectly built, blueprinted car. With the car sitting on a flat, level surface, with no passengers or loading on the car, and perfectly matched suspension, then the roll bars will be in a neutral position and the distances between the roll bar ends and suspension attachment mounts for the drop-links will be identical, so the manufacturer fits two identical length drop-links which fit without any issues.

Now undo one end of the drivers side drop-link and get the driver to sit in the car. Lets say an average 95 Kg man. The drivers side suspension is compressed by 95 Kg and with a 100Kg/25mm spring fitted, the car will sink maybe 10 – 20mm due to his weight. Now try refitting that drop-link! It will be too long so you will have to compress the roll bar downwards by the same distance to refit the link, therefore pre-loading the bar.

Now, when approaching a corner, the roll bar is actually trying to roll the car by 95 Kg in one direction and by -95 Kg in the other, so during cornering, the weight of the car needs to shift by 95 Kg before the roll bar becomes neutral. In other words, as you corner, the roll bar works in one direction for the initial turn and then in the other once past the pre-load point upsetting the predictability and smoothness of the turn as the bar goes through this transitional state.

With an adjustable drop-link, (and only one is necessary), you remove one side drop link, sit the driver in the car and fit the adjustable link, setting the length so that it fits without pre-load to the car. The car is then set-up for neutral body roll when that driver is using the car. The adjustable links also take into account any slight manufacturing tolerance differences between the springs and can also take into account worn, aged and sagging springs.

The principle is as equally relevant to the rear of the car as it is to the front although this would be less noticeable when driving. These types of adjustable links also have the benefit of being able to replace end joints individually should they wear rather than replace the entire link.

Shown below is a pair of front and rear drop-links for the BMW E53 X5 from PhoenixMotorsport, and all our kits will come with Grade A2 or A4 Stainless steel washers and nuts so that any future maintenance will never be met with corrosion or siezures, even from off-road use.

As I will be installing the polyurethane subframe and thrust arm bushes next weekend, I thought I would give these a go whilst the car is apart and then I will get an alignment done. Will do a post on the whole install and post for you.

X5Girl, xxx