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moving front ARB droplinks onto wishbones

Shocks, Springs, Brakes, Frame, Body Work, etc

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sambeeb
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moving front ARB droplinks onto wishbones

Post by sambeeb »

Hi,

My VW Polo gti has its front anti roll bar acted on by long droplinks that come down from strut flanges. I'm going to move away from this system to where short drop links coming off the wishbones will act on the FARB. In the proposed system the droplinks will be coming off the wishbone roughly half way along its length. The current system acts on the bar via the strut. Most Mac strut front ends have a movement ratio of 0.9 so for say 10mm of wheel deflection the spring/strut body will move 9mm. That'll translate to pretty close to 1:1 of wheel:bar movement. The proposed system for that 10mm of wheel movement will probably only move at the bar by half that but to my eyes will have more leverage over the bar too yes? Am I correct in that?
If so, and I'm aiming to retain the same roll resistance from the FARB, under the new system I would theoretically have to move to a stiffer bar yes??

sam
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MadBill
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Re: moving front ARB droplinks onto wishbones

Post by MadBill »

Connecting at the midpoint of the wishbone will give a motion ratio of 0.5:1, so the bar would have to be almost twice as stiff to have the same effect.
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dannobee
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Re: moving front ARB droplinks onto wishbones

Post by dannobee »

Not to pick nits, but the equation is the motion ratio squared. (9/10)^2= 0.81 If the point is changed to halfway, (5/10)^2 = 0.25
The bar will need to be over 3 times stiffer. This can be accomplished by running a stiffer bar or moving the other end of the link closer to torsional center of the bar (i.e. shorter "arm length" of the sway bar). Or both. He'll need to do the math on the bar if he wants it to handle the same as before.

I'm sure there are online calculators out there for computing bar stiffness. Compare the before and after stiffness for each scenario.

If you're familiar with Excel or something similar, make a page with the inputs and make one function cell to spit out the answer.

Since aftermarket bars often have multiple holes (or slots) drilled in the arm ends, or have a bar clamp end allowing infinite adjustments within the range, it's something you should compute and jot down in your notebook for future reference.
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MadBill
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Re: moving front ARB droplinks onto wishbones

Post by MadBill »

I knew that. Even built adjustable attachment points for my Camaro with a long link and a number of mounting points along the wishbones.:oops: :oops:
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