Swaybar & Endlink FAQ
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This is a discussion on Swaybar & Endlink FAQ within the Suspension & Wheels forums, part of the Tech & Modifying & General Repairs category; Well guys, I have intended to put a few FAQ threads together to help everyone with some basic suspension upgrades. ...

  1. #1
    Registered User wrx wagone's Avatar
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    Swaybar & Endlink FAQ

    Well guys, I have intended to put a few FAQ threads together to help everyone with some basic suspension upgrades. This shall be be the first of these.


    Intentions of this post:
    This swaybar and endlink FAQ will explain the basics of how swaybars work (what function they have in your vehicle's suspension) and the effects of changing them can/will have on the handling of your vehicle.

    Note: This information is gathered from my personal experience with different swaybar setups on both street and AutoX and from the experience of others on this forum and other forums. It is intended only to used as a guide. You as the end user are ultimately responsible to understand the handling of your vehicle and the effects of any changes that you make. Please research all of your modifications carefully and select the modifications that you are ultimately comfortable in installing on your vehicle.


    What do swaybars do?
    Swaybars (anti roll bars, stabilizer bars, etc.) limit the amount of body roll your vehicle will exhibit while cornering by increasing the roll stiffness of the suspension. The swaybar is attached to the suspension arms to limit the independent movement of these arms.



    As the body of the vehicle rolls into a corner the loaded suspension arm (outside wheel) will apply an upward vertical force into the swaybar while the spring of the opposite (unloaded) side will apply a downward vertical force. These opposing forces create a torsional deflection in the swaybar. A larger swaybar is better able to resist this torsional deflection and therefore will transmit more of the force from the unloaded spring into the loaded tire limiting the amount the body is allowed to roll. The stiffness of your springs will directly affect the effectiveness of your swaybars.

    Please read for more info: http://en.wikipedia.org/wiki/Sway_bar


    How does a larger front swaybar affect performance and will it cause understeer?

    First point: Body roll is caused by weight transfer.

    Second point: A tire's grip is created by:
    a) The coefficient of friction between the tire and the surface it is in contact with. (These for the intent of our discussion are constant)
    b) The normal force applied to the tire's contact patch. (ie. weight transfer)

    Third point: The WRX uses a MacPherson strut style front suspension. This suspension design, due to the upper suspension mounting point being the top of the strut assy. located at the top of the strut tower, suffers quite a bit of camber loss due to body roll in corners. A larger front swaybar will limit this camber loss to allow the tire to maintain its contact area in the corner. This increase in available contact area outweighs the loss in weight transfer (less body roll) to that tire.

    So, the answer is both yes and no.
    Yes - The increase in roll stiffness will limit the camber loss experienced during cornering, thereby allowing the tire to maintain a useful contact patch, provide more grip and ultimately reduce understeer.
    No - To much roll stiffness will not allow enough weight to transfer to the tire and the car will understeer.

    There is a fine line to this and the ultimate answer rests on a number of variables such as:
    a) The type of driving you do. (ie. Street, AutoX or Track)
    b) The overall roll stiffness provided by both the springs and the swaybars.
    c) The roll stiffness of the rear end of the vehicle, such as the tendency to oversteer.


    How does a larger rear swaybar affect performance and will it cause oversteer?

    Short answer: Yes, on a WRX a larger rear swaybar will cause oversteer. The larger rear swaybar accomplishes this by increasing the roll stiffness and reducing the weight transfer to the tire reducing grip. The level of oversteer experienced can range from making the handling more neutral and balanced to outright snap oversteer. It is all based on the levels of front grip and the balance to the rear grip.

    However to contradict myself, if you are running rear camber (approx. -1.0 or less) a softer rear swaybar will allow more body roll and this will result in a decrease in camber reducing the contact patch of the tire. This reduced contact patch will lessen the tire's grip and can cause oversteer.


    What are the difference in solid vs. hollow swaybars?
    Weight & price. Seriously.

    A hollow swaybar can be manufactured to be just as stiff as a solid swaybar, it is just more costly to do so. Tube/pipe is just simply more expensive than bar. Tube/pipe is also only available in limited sizes, therefore it does not provide as many options to the designer.

    The only benefit of a hollow swaybar is the weight savings, all else being equal.

    Whiteline technical article.

    Who makes the "best" swaybar?
    A swaybar is a swaybar. It is simply a bent piece of steel bar with some holes at the end. The only real requirement is that it fits. Most major manufacturers do not have any fitment problems at this point.

    I will not list manufacturers as I do not want to favor any manufactures/vendors. Please search the threads and/or PM our vendors to find info on the manufactures and pricing. I'll say it again, please support our vendors, they ultimately keep this site running.
    Last edited by wrx wagone; 09-12-2007 at 10:49 AM.
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    Registered User wrx wagone's Avatar
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    What swaybar(s) should I get?
    Before one can make this decision, one must consider the following things:

    1. The suspension is a SYSTEM. Suspension tuning is very much a black art based on numerous variables even including very individual things such as personal preference and driving style. You need to consider these suspension modifications as how they will have an effect on the vehicle dynamics as a whole. The vehicle handling is directly related to tire grip which as previously mentioned is all about the tire's contact area and the forces acting on that area. Springs, swaybars, alignments ALL have an affect on a tire's grip and need to be considered as a complete system.

    2. The intent of the modification and/or the intended use of the vehicle. A street setup is very much different than an AutoX setup is very much different than a track setup. You are asking the vehicle to do very different tasks. Compromises will need to be made to make the vehicle excel at any of these things specifically.

    3. Your starting point. The stock WRX typically comes with a 20mm front bar and a 17mm rear bar. The '02 WRX & some early '03 WRX sedans came with a 20 mm rear bar stock. The STi comes with 20mm bars stock.

    The swaybar recommendations I will make should be used as a guide to help a novice user select the swaybars that are appropriate for the anticipated type of use the vehicle will see.

    Note: These recommendations are largely based on my personal experience and on the assumption that the vehicle is using springs (<300 lb/in) and struts. The use of stiffer springs (ie. coilovers) will not require increasing the swaybar size as much to provide the same level of roll stiffness. Stiff springs in combination with large swaybars can provide WAY too much roll stiffness and have very negative effects on the handling of the vehicle.

    My Recommendations:

    Street: 20mm - 22mm adjustable swaybars both front and rear. These bars will provide improved handling and still provide predictable road manners.

    Street/Some AutoX: 24mm - 26mm front bar & 22mm adj. rear bar. The larger front bar will provide both better turn in and reduced understeer. The rear bar can be adjusted stiffer if desired to increase oversteer (rotation) in corners.
    Note: Both of these handling changes are useful on the AutoX course but can (to some) make the car dart into corners, feel more twitchy or make the rear end more loose. The driver should pay particular attention to off throttle oversteer.

    AutoX: Biggest front bar you can get, 27mm or larger. 24mm adj. rear bar. The larger front bar will provide both better turn in and reduced understeer. The rear bar can be adjusted stiffer if desired to increase oversteer (rotation) in corners. Stiffer springs should also be considered at this point as well.
    Note: These large bars pose some serious considerations to the street manners of the vehicle. The front end of the car becomes as I can only describe as "wiry". Wherever the front tires are pointed the car goes. This can be particularly cumbersome on highway or uneven pavement conditions. The front end begins to exhibit understeer on high speed corners. Also on uneven pavement such as turning in a steep apron or going diagonally over the crown of the road the stiff bars can actually cause tires to lose contact with the pavement as they will limit the suspension movement. The rear end of the vehicle exhibits similar response as above.

    Track: One should very much consider stiffer springs for track use before going with larger swaybar(s). The swaybar(s) used will need to be ultimately selected with the stiffness provided by the springs in mind. That being said, I would NOT go any larger than 24mm.


    Do I need upgraded endlinks?
    Maybe. The purpose of the endlinks is to attach the swaybar to the suspension arm to transmit the forces applied to one into the other. Therefore all the forces applied to the swaybars will be transmitted through the endlinks.

    The stock endlinks are replaced because the stock units are very flexible and the force that should/could be applied to the swaybar and/or suspension arm is wasted flexing the stock endlinks. Also the stock endlinks can break when used with much larger bars than stock.

    My Recommendations:

    <22mm swaybars: meh.

    22-24mm swaybars: Maybe. This decision should be made between your desire for performance and your wallet's desire to remain full.

    >24mm swaybars: Yes.

    Again please PM our vendors to get manufacturer info and pricing.


    I do not in any way believe that this post covers all the information available, yet I do hope it can act as a guide to our forum users to understand swaybars and how they can influence the handling of their vehicles.

    If you have any questions about any information about any of the material covered in this post, please start a new thread in this forum and we as a group can discuss it. If the information proves useful to this topic, I will edit this post.

    If you feel I have made any errors or need to clarify information presented in this post, please PM me. I both make errors and am also continuing to learn about the various aspects suspension tuning.

    Thanks to ButtDyno whose info helped with this sticky.

    and thanks for reading.

    Other recommended reading:

    Whiteline Swaybar FAQ
    How Stuff Works - Swaybars
    Last edited by Weasel 555; 04-10-2008 at 12:16 PM.
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