Quote:
Originally Posted by bigjimzlll
While I'm not an expert on suspensions...my understanding is all the spring does in the rear is to hold up the truck. The shock controls how much seperation(anti squat) or compression (squat).
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Jim,
I hate to say this, but that is not how I understand it. Seperation and squat are relative to the instant center of gravity vs center of gravity. If your instant center of gravity line (which for our trucks is a line drawn from the rear tire contact patch through the front hole on the lower control arm) is bellow the center of gravity than you will induce squat, if it is about, you will induce seperation.
For a ladder bar car, your ICG is where upper and lower are welded together. For a 4-link you have to draw a line for the upper and lower arms. Where they meet, that's your ICG.
The spring will see a different leverage ratio if placed in front of the axle centerline or in the rear of axle centerline. It will see different leverage ratios based on different distances in front IE different distances behind. The weight placed over the rear (or front for that matter) will act differently on that spring due to location. In our rears, with the stock mounting position, There is quite a bit of leverage placed on the spring compared to if the spring was behind the axle. This requires you to have a stiffer rate spring in the stock location or a longer spring of the same rate vs if it were behind the rear. But, due to the leverage ratio, if you are able to induce antisquat, having the spring in front of the axle will give you more potential travel. Same goes for the shock.
The shock is controling the rate the suspension travel. Now if your shock is in front of the axle, it is subject to more leverage ratio as well as the spring. The shock is going to see less speed in front of the axle vs behind it but requre a stiffer setting to act the same as it being behind the axle in a softer setting.
What I'm getting at is with out your ICG/CG being 100% your are going to squat the rear and loose energy planting the tires in to the suspension. If you are trying to get sepperation, you need at least 101%.
Paired with the right spring having stored energy and a soft setting for expansion rate on the shock, you are going to allow the rear to seperate quickly forcing the tires in to the ground lifting the rear frame.
If you get a chance, Dave Morgan sells a book called "Door Slammers: The Chassis Book" He also has just released a DVD out based on one of his seminars. He has been doing chasis for Alston for the better of 15 years. He explains it much better than myself..