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  1. #1
    Regular Member tassie_bb1's Avatar
    Generation
    4th Gen
    Model
    VTEC
    Join Date
    Dec 2013
    Location
    Tasmania
    Posts
    205

    To brace or not to brace

    I know the question has been asked a billion times, the question for me is not so simple. Being one of the cheapest suspension mods possible many people rush to throw on a front and sometimes rear tower braces on without thinking too much about the possible benefits. Not everyone who has one says how amazing they are and how much it changes the feel of the car, so I want to dig deeper. Sorry if this starts to read like a suspension 101 FAQ but I figure it's good for those who don't know and it helps me sort out the facts in my head.

    We all run with double wishbone front and rear suspension, it's just one of the things that make Preludes great. When cornering, the outside wheel takes the weight of the car making the suspension compress, but also the top of the wheel wants to tip out as the friction of the tyre on the road pushes the car around the corner. Rather than having a portion of these lateral forces being transferred directly through the top of the strut (as with a Macpherson system), the forces making the wheel want to twist are counteracted by the upper control arm which mounts further down in the tower. I would assume judging by the relative flimsiness of the UCA's that most of this force is transferred through the LCA, since the UCA is at the top of a big lever (the knuckle arm) so it can do a lot of work without much effort. This all creates some very interesting suspension geometry characteristics which I am only just beginning to understand, such as having a smaller radius UCA compared to the LCA can actually increase the amount of negative camber as the suspension compresses. Now with a Macpherson strut setup all these cornering forces transferred in to the top of the tower create a lot of unwanted stresses in the bodywork and as such it is a very good idea to brace to the other side of the car. Many manufacturers who run with a Macpherson setup offer a strut brace either standard or on their performance models. The idea being that a box with a lid is more rigid than an open box. On double wishbone, there aren't any clear answers.

    So, I ran an experiment. I measured the distance between two fixed points at the top of the towers, then simply jacked one side of the car up and measured again. My thinking was that with one side of the car fully unloaded that it might induce at least a little chassis twisting. I admit that it's not a great test since all I am doing is slightly overloading one side of the car and transferring the load on the other into the jack and into the ground, but there was no movement whatsoever. I'm thinking next is to jack up one side of the car and set it back down on some bricks, this should hopefully load up one side of the car to a greater extent. If anyone can come up with a better test I'd be happy to use my car as the guinea pig too.

    Now I know a lot of people would say "**** it, it's only money just buy the damn thing and quit being a little bitch" but;
    1) Screw you, don't call me a bitch.
    2) I prefer to research the engineering behind mods where I can.
    3) The weight saving is important to me, this is for a track car after all.
    4) I am not in the business of pissing money up against the wall (except in the case of point #3)
    5) isn't it nice to have a greater understanding of how these things work?

  2. #2
    PA Janitor Bob's Avatar
    Generation
    3rd Gen
    Model
    Si 4WS - B Spec
    Join Date
    Jan 2006
    Location
    Western Australia
    Posts
    11,090
    I could feel the added stiffness in the chassis with the braces.
    It won't make your car faster, but it will give you more direct feedback. If you can feel what the tyres are doing then you are more able to respond.

    The Whiteline website has some excellent reading material. Take a look at the articles on Suspension secrets.
    http://www.whiteline.com.au/suspensi...egory=Articles

    This is the first article on the subject. Ref pg 6.
    http://www.whiteline.com.au/docs/art...sp_01_0202.pdf

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