20mm adj rear swaybar to suit wrx's - specify model year when ordering

Formerly Selbys Swaybars, Whiteline Swaybars are descended from this long standing quality brand name. The one and only Selbys Swaybars have been around for quite a while. In fact, we can trace our lineage back to 1965 but our development of swaybars continues into the new millennium under the Whiteline Swaybar brand.

The Whiteline Swaybars brand is proudly owned and manufactured by Whiteline Automotive here in Sydney Australia. The range consists of swaybar kits, custom bars and parts covering the biggest range of applications in the world. Only genuine Whiteline Swaybars are supplied in our signature "Silver Sparkle II" metallic powder coat colour.

The original Selbys Swaybars are also still available in a limited range of fast moving applications. Contact us for further details.


WHY FIT BIGGER SWAYBARS?

Fitting a Whiteline swaybar offers allround improvements in handling, tyre wear, comfort, safety and even load carrying. It's the best dollar for dollar handling improvement you can make.

The fitting of larger swaybars (rear and in general) has two main effects, vehicle balance in terms of understeer and oversteer, and increased roll resistance. Both of these can provide increased overall grip levels that can be achieved by the vehicle.

As most factory vehicles are biased towards understeer, fitting of the larger rear swaybar will help in providing a more neutral characteristic in the handling at the limit. 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.

At first this may sound sacrificial, however, as 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. In the end an increase in overall grip can be achieved by balancing the vehicle. A WRX or other front torque biased all wheel drive vehicle will benefit even more due to combined front end steering/traction demand.

Another effect of introducing larger rear bars is that the roll stiffness is increased, and chassis roll is reduced, this also reduces the effects of "roll camber". Roll camber is the variation in the wheel/tyre camber setting due to chassis roll, and during cornering usually results in the outside wheels gaining positive camber.

By increasing the roll stiffness and reducing roll camber effect, the wheel/tyre stays closer to its wheel alignment setting or optimal setting. This can increase the overall cornering grip available, as the wheel/tyre does not lose as much negative camber at the limit.

The balance (and grip increase) of the car could also be achieved by reducing the front swaybar stiffness, however its roll stiffness would be reduced and roll camber would suffer. This would lead to large amounts of positive camber being gained on the outside wheels/tyres when cornering. This would result in a wheel/tyre that would not be at its optimal camber setting at the limit of handling.

This could be remedied with large amounts of static camber to counter act the positive camber gain, however the resulting tyre where, and straight-line handling effects would suffer.

To maximise wet weather grip, a softer overall setting would be required from dry settings. The reason for this is that a wet track cannot give the same friction values as a dry track and therefore overall grip will never be as high as in the dry (hence the amount of chassis roll will be lower as well). The suspension can therefore be soften slightly until the camber setting start to be compromised due to camber roll.

So to conclude a larger rear bar in the wet should leave the car balanced however it would be slightly disadvantaged due to the high stiffness.

HOW BIG A BAR DO I NEED AND HOW WILL IT WORK?

Lets start first by assuming that every vehicle has a certain optimum "anti-roll" value, typically expressed in pounds or kilos. Don't ask me the ideal for the WRX as there are many formulas that have to take into account the COG (centre of gravity), RC (roll centres), the resultant roll couple and roll axis front to rear. We at Whiteline establish this optimal amount thru experience and testing though we are starting to use more computer modelling software to fast track development. With this amount in hand, the next issue is to determine where these amounts are needed and under what circumstances.

Best next to jump to the issue of cornering and how much we need where and when but its important to first identify that we need to split any given corner into at least 3 segments. Corner entry is that first phase where you initially turn in, you are generally decelerating either under brakes or on a trailing throttle. Needless to say the weight shift is moved toward the front. Mid corner is when you start aiming for the apex proper with either a neutral pitch (for-aft weight or movement mode) stance or slight power application. Corner exit is once you seriously start applying power and can be either just before the apex or after. Either way, the main steering line has been established and corner exit power is being applied to maximise forward speed. Accepting the above, its equally important to then segment handling bias according to corner position. That is, a mid-engine car with factory setup will typically understeer on "corner entry" and "middle" stages but very easily oversteer on exit if too much power is applied.

Understanding that everything is a compromise, it is useful to have a disproportionately high rear roll rate on corner entry to deliver more front roll to improve initial turn-in "bite" through the front outer. A heavier front spring like a lot of front anti-roll, will act to oppose the momentary (as little as a 1/10 sec) weight transfer required to give that "bite" which can result in more turn-in understeer. On the other hand, corner exit is all about maximising grip in longitude and latitude with throttle steering used to optimise outcome. Here, disproportionately more rear roll control acts to load the inside front (particularly useful on a fwd and WRX) as the outside rear is held more upright.

The correct total amount of "anti-roll" is inclusive of spring rate, which complicates the issue but it is still safe to assume that it is better to start with less spring rate than too much. The object is to maximise grip through adequate suspension travel at each wheel, a heavier spring rate makes it difficult for an individual wheel to react to changes in road surface under roll so contact is lost. Having said that, there is still no absolute correct number or recipe with two different racecars in any 2x car leading race team using largely different setups depending on the driver's preference. However, in most cases it will still function within a certain optimal pie of anti-roll force.

MULTIPLE ADJUSTMENT HOLES ON WHITELINE BLADE SWAYBARS

A swaybar is actually a torsion spring not unlike a coil spring. Imagine you could uncoil your coil springs, and then hold each end and twist. This is pretty much what happens with the coil when it does its work as the shape forces the material to twist through out its length as it's compressed.

Going back to our straightened piece of spring steel, with your arms holding each end, imagine that each of your arms represent the swaybars "arms" and the spring steel rod represents the "back" or centre portion of the bar between the arms. As you try to twist the ends, a certain amount of flex happens in your arms but most of the action happens across the back of the bar. Hence, the formula calculating swaybar rates requires a value for the length of the back of the bar as well as the length of the arms.

The formula does not allow for a left or right arm value, just a total that acknowledges that the total arm length vs. the back length is the key calculation affecting the rate. We know that shortening the effective length of the arm by choosing a hole closer to the back of the bar will reduce the leverage ratio hence increase the rate but this affects the total arm length so can be done on one side only. In this way, a 2 hole per arm Blade adjustable bar does actually have 3 different settings; a 3-hole bar has 5 different settings. Additional mounting holes on the chassis end multiply the options further.

There are some assumptions and exceptions to these examples, specifically the issue of ultra short arm lengths and its effect on suspension preload. That is, asymmetric adjustment can preload the suspension if the arms are very short. The other issue is that the bars arms also deflect so that is taken into account by the formula but the amount of deflection is governed by the size and shape. Friction and deflection in mounting bushes will also affect the bars outright behaviour.

You may also notice that some of our adjustable use a longer Blade (flattened area) than others. We use this to fine-tune the adjustment range as the Bladed portion deflects a lot less than the simple round bar. (Think of a structural steel I-beam). Even the height and width of the Blade is used to tune the final outcome when designing new bars.

As for different materials, our XRD swaybars use 27mm base material machined down to 24mm outside the chassis D mount points coupled with a specific Blade length to deliver a very broad range of adjustment through a more progressive working curve. This delivers a hybrid outcome tunned for a particular result and is another design tool we can use.

It's therefore important to understand that a 22mm physical diameter swaybar can be made to behave like something totally different just by changing the shape of the bar and its ends. Adjustable bars are a very useful suspension balance tuning tool and a better understanding of how they work should help you get a better result.

ASYMMETRIC SWAYBAR ADJUSTMENT USING ADJUSTABLE BARS

Having a number of hole options on each end of and adjustable swaybar gives you a number of tuning options. The most obvious has already been discussed elsewhere but its useful to also understand what happens when you use asymmetric adjustment.

Asymmetric is the opposite to symmetric and implies the use of differing holes on each side of the swaybar. For example, this might involve setting the left hand side to the hardest setting of 3 while the right hand side might be set to the middle setting. Contrary to what some people think it does not equally split the rate difference between symmetrically using setting 3 and setting 2. That is, the resultant rate is also asymmetric with more roll stiffness on one side compared to the other.

SWAYBAR PRELOAD ADJUSTMENT - RARELY A GOOD IDEA

Preload of the swaybar implies that once installed the bar is loaded in torsion and applies load to the suspension system. The static result of this is that the body or chassis has been preloaded in roll and may be at a visible angle if the preload is large enough. This preload also effects the weight distribution at the tyre contact patch, both left and right and diagonal.

Dynamically the sway bar will be able to resist roll in one direction much greater than it would if it where installed without any preload. However cornering in the opposite direction the bar will allow and promote chassis roll until it has unwound or “used up” its preload, at which point the swaybar is unloaded at some cornering level. Beyond this the swaybar will provide the usual roll resistance or roll stiffness (less than a non-preloaded swaybar).

This effect is very asymmetric, although actual amount or effect it has could be minimal. The possible reasons for such a design could be to match a chassis which has its CG offset to one side, compensating any effects of that. It can also be used to modify the handling of cars that run on specific tracks, like oval racing, which benefit from asymmetric setups.

Whiteline swaybars are designed to provide no preload once installed, giving symmetrical roll resistance. We have not encountered any OE swaybars that are designed by preload.