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Discussion Starter · #1 ·
I'm putting a set of shocks on a 4 bar rear suspension. The shocks I will be using have bushings at both ends with a mounting bolt that goes thru the bushing. Hope I made myself clear there. Question is: should the top and bottom bushings be parallel to the rear end? Shocks will be mounted vertical looking at them from the back and 10 degrees forward tilt top to bottom. My thoughts are that the shock mounting bolts can rotate as the rear end goes up and down. Or should I mount the top parallel to the rear end and bottom perpendicular to the rear end to allow for some body roll?
 

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Which direction has more movement , up , down travel or body roll ? Mine are perpendicular , I've seen a lot of factory stuff both ways . A guess would be more movement with body roll , so shock bolt perpendicular to body roll ...
 

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Discussion Starter · #3 ·
Yes, I'm beginning to think the same way. There would be more body roll than movement due to suspension travel. What about the top in one direction and bottom in the other?
 

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Ok you are asking for a very simple answer to a very vehicle specific question.

There are entire books written on suspension design.

First we need to start with your 4 link design
Then we need to look at the weights involved
How those weights affect the car under acceleration and cornering
Your intent of the car( a street car and a quarter car will have different needs)
And about 20 other factors before we can even talk about shock location, valving, and roll control

Here is the super generic ultra short version.
You want to set up your shocks and springs so that the suspension can run through its predetermined travel without binding.
That is it make sure nothing is going to bind is the first place you need to start. Sounds simple right?
Well not in most cases. In most cases the arch of one suspension component is not going to match the other at some point in the travel. Now you can reduce this binding. But generally there is some binding at some extreme. Which is why we have bushings to "buffer" things and twist things in a good way.

Shock placement and shock dampening/design is going to come down to the leverage your 4 link is placing on that shock.
To keep things simple lets say we have a parallel 4 link with equal arms with watts link on a straight axle. That axle is going to follow a arch until the wattz no longer allows. We take our shocks and set them up so they also follow that arch and we have axle that will drop straight down. If you corner then the axle is still dropping straight down only one shock is being loaded while the other is being unloaded. I am not going into single and double reacting shocks. But lets say we have double reacting shocks where as one side is compressed and the lets say nitrogen is moved from the bottom to the top the other shock is being "unloaded" with the nitrogen moving from the top to the bottom. Both of these shocks are doing work to get that axle back to it's predetermined neutral position.
Now when these shocks(or multiple shocks/different valving) are not enough then we get into a sway bar. Very condensed version of a sway bar is a bar that attaches to the frame. You have some type of arms that attach the bar to the axle and in some cases these arms are the bar itself. This sway bar system is designed to act as controlled binding. As you take a corner hard the suspension does it's work until the arms no longer have travel and the sway bar is acted upon. At this point the sway bar bushings are forcing the axle against the road while the bar itself is "pulling" the light un sprung side of the car down to control body roll.

While you may think a sway bar is horrible it creates binding and adds weight. It's affect on handling is noticeable and when properly set up binding is minimal.

So we have our equal parallel 4 link, our watts link, our double reacting shocks with adjustable valving, and our sway bar with adjustable links. We know where our weights are and how they are going to affect the suspension.
What we need to do is drop the axle through it's travel and determine just what we have as far as leverage on these shocks then and only then can you determine the angle those shocks can be placed at that works within that arch.


This is one of those things where it is terribly hard to explain if your not under the car or driven the car. I fine tune suspension with a video camera looking for binding and loads that you just may not notice on a lift or butt dyno. But first you need to get that suspension close using basic math, some geometry, and then tailor it to your application.



Short version of what turned into a long post is you need to grab a couple books(or e books) on suspension design related to your use and suspension. Read through those a couple times even building a scale version of your suspension if need be. Apply what you have learned to the car to get you close to a close to perfect setup. Then test and retest oh and test some more till you have the suspension set up to what fits your needs.
 

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Which direction has more movement , up , down travel or body roll ? Mine are perpendicular , I've seen a lot of factory stuff both ways . A guess would be more movement with body roll , so shock bolt perpendicular to body roll ...
The main reason for shock absorbers is to control the unsprung weight so the tire remains in contact with the road . having the shocks placed as close as possible to that unsprung weight ( wheels& tires) is important . the more angle away from vertical , the less effective the shock is .
Well crap , I hit the wrong post to reply , you get the idea ..^^^^
 
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