Anti roll

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Page created by unknown September 23rd 2005:

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HR Front Suspension. The Front Sway bar is to the right. The Stub Axles are from an LH Torana. Photo by HQ_SS. Click to Enlargen.

 

Anti Roll:

Most people think anti roll bars are only to stop the body leaning toward the outside of the corner while cornering... Sure this is part of their job but they have another significant role that most people don't realise.

Their other job is to tune how the car handles when cornering hard and the anti roll bar(s) fitted will determine whether the car will tend to oversteer (hang the back out) or understeer (plow forward without turning).

To understand how this happens you need to understand what causes understeer and oversteer. 
HZ Disk Brake Salisbury Rear Axle and Sway Bar.  Photo by Leroy. Click to Enlargen.
 

Understeer:

Understeer is essentially caused because the front tyres lose traction and start to slip before the rear tyres and results in the car plowing forward without turning. Too much understeer isn't especially dangerous but it greatly reduces the cornering ability and places extra load on the front tyres causing them to wear bit faster.

Oversteer:

Oversteer is the opposite of understeer. Oversteer is where the rear tyres start to slip before the fronts and is dangerous because it can easily cause the car to lose control and spin into the scenery. Oversteer can easily be induced in a rear wheel drive car by accelerating while cornering, and in this case is called power oversteer. When car makers choose the anti roll bars they usually aim to make a car understeer slightly when right on the limit of adhesion, which gives the driver warning that they are at the limit of the car, and is easier to correct. 

Tyre Slip:

The tyre slip that causes understeer and oversteer occurs when the tyres are loaded beyond their capability. The load on a tyre while cornering affected by things like the front to back weight slip of the car, relative stiffness of the front and back springs and relative stiffness of the front and back anti roll bars. The weight distribution can't easily be altered and the stiffness of the springs is generally determined by the weight it has to support so it is the job of the anti roll bars to tune the handling.

By making the front anti roll bar stiffer (ie thicker) weight transfer is increased to the front outside tyre during cornering meaning the car will understeer less. Conversly, increasing the stiffness of the rear bar will increase weight transfer to the rear outside tyre and make the car oversteer more.


So what does all this stuff have to do with my holden?

If you fit a larger anti roll bar to the front or back of your car you should fit a larger one to the other end too!

Ideally they will be a matched pair for your specific model or will be adjustable so you can tune them to suit.

For example if you have a pre RTS HQ/HJ don't fit the larger RTS front anti roll bar unless you also fit the RTS rear anti roll bar too. Sure it will make you car roll less in corners but it will also make it understeer a lot more. By the same token don't install a rear sway bar and leave the smaller non RTS front anti roll bar because you may create a tail happy 'drift' machine.

Changing the stiffness of the springs at one end of the car will also alter the handling. Again changing the springs with a full set, or least by a similar sort or amount will minimise the effect on the handling.

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