Yes, I did a search. Surprisingly, it turned up nothing, but I'm sure this topic has been covered.

So.

I think I understand what pre-load is. What I don't know, is how to identify it and how to correct it. I'm sure it's an installation procedure. I installed my big(ger) rear sway early last year before I even heard the word pre-load. I'm sure I f#$ked it all up.

 

its when you tighten down the sway bar on one side.
It can change how much your car understeers

 

does it make a diff if the end links to the bars are tightned w/ or w/o load on them (as in the car on or off the gnd)?

 

Yeah good topic I'm interested

 

my understanding is basically this... when you plunk yourself in the driver's seat of the car, you're going to weight one side of the car more than the other. I believe to take the preload off, you are supposed to loosen the swaybar endlinks up a bunch. While you are sitting in the car, have a friend look at the endlinks. They should be at different distances from the mount itself. Have the friend rotate the swaybar until one end is in the proper position and tighten that endlink. There should still be a gap on the other endlink. This is where the preloading comes into play. When the endlink is tightened, that gap is removed, placing a load on the swaybar. Thus the preload. What you do is slip a stack of washers onto the endlink mounting bolt to take up this slack. I've read that fender washers are good for this. Once you have filled the "gap" with the washers, you can cinch the swaybar endlink back down without putting any preload on the bar. Hope that helps.

 

WRXRacer111's explanation is pretty darned right on, based on my knowledge but I just like to play these things out as an exercise to see if I can explain them.

An antiroll bar (ARB or sway bar) is a torsion bar spring and works because it resists being loaded tortionally (in twist). As the car rolls, the outside wheel - thinking just of either the front or rear end for now - travels more, relative to the body, than the inside wheel. The ARB's torsional resistance acts by effectively pushing upward on the inside wheel, attempting to equalize the movement on each side.

(Right here, I know that I should be able to say something sensible about weight transfer but it has been a while, I've forgotten, and I need to go back to the books in the boxes downstairs! See? I learned something.)

If, when the ARB is installed, it is twisted one direction or the other (when viewed from the end), then it is "preloaded". If this is the case, then when the car rolls one direction, the first little bit of movement is effectively taking out the preload (the twist that it started with) before it can start doing its torsional resistance thing. When the car rolls the other way, the bar starts doing its job with some twist already in it. The roll rates, left to right, will be different, so the car will understeer relatively more (or oversteer relatively less) in on direction...

Under ideal conditions - assuming that you want the roll rate of the end in question to be the same in both right- and left-hand corners - you want the ARB to be "untwisted" when the car is static with the driver and fuel in it. That is, it should be just as loaded as it was when it was sitting on the floor of the garage before installation - i.e. not at all. This can be adjusted (depending on how the bar mounts) by changing the length of bar-end links or shimming things like WRXRacer111 described.

In the real world with 3000# cars and relatively soft bars and springs, this is a pretty minor issue and, unless you have already balanced your corners weights, you should do that first - it will make a bigger difference probably. When you DO check your corner weights, ARB preload effect is an argument for disconnecting the links before doing so.

Excellent question. Now, off to the books...

Kirk

 

forgive the ignorant question, but doesn't running some toe out in the front or rear (or both) wheels help to "pre-load" the suspension, which aides in turn-in? I realize this may not be the same thing as pre-loading the sway bar, but isn't it a similar principle?

 

Correct me if I'm wrong, but I don't think the toe settings preload the suspension so much as they aid in tire slip-angle management.

LOL, Kirk wrote out the explanation I briefly thought about writing before I realized I had way too many other things to do. Good stuff though.

The reason I brained this one out a whole bunch is that I was planning to do that take the preload off my Subaru front swaybar. I went to the store to get fender washers, then realized I needed to take a look at what size I need. At that point I realized that Subaru uses a horizontally mounted drop-link setup on their swaybars which you cannot shim. I presume this is for ground clearance. In order to take the preload off that setup, I'll need a vertically adjustable drop-link. Oh well, that'll be a summer project for me to fab.

 

Which side do you put the washers on? The one you attached first or the one with the gap. Having trouble visualizing this. Matt confuzed. Is this done with the car on the ground or with the back end in the air and the suspension in full droop? I'm thinking there's got to be a way to do the correctly without these washer things. Gotta be.

I'm exhausted. I'll come back tomorrow, re-read it and hopefully it'll make more sense.

 

It's doenw with full suspension load. Car on the ground or on ramps, etc.

WRXracer111 hit the nail on the head.

We can play with it this weekend in Laurinburg if you want. It is a subtle thing, but is one of those deals you want to do to make the car turn the same left and right.

Depending on the kind of endlinks you have, you might not be able to change anything. The old washer trick only works with old end links. Most cars are now using some sort of a heim joint on each end of a solid rod. The only way to adjust them is by making a custom set that has an adjustable rod...

Scott

 

On formula cars, GT cars, stock cars and such, it is common practice to use a ARB "drop link" (good term) that has a left hand threaded rod end on one end and a right hander on the other. This allows you to adjust its length without disconnecting it - like the steering tie rod adjustment for toe.

K

 

Yup, that's what I'm talking about. From the pictures, it looks like Tein actually ships endlinks like that with their HA coilovers.

Scott

 

This is a bit cryptic, but I don't have time to make it look really pretty. Someone else can do that.


Might help to visualize the process.

 

If the anti roll bar wasn't under any torsional stress during/after installation and the driver does not weigh several hundred pounds, this sounds like some heavy-duty hair splitting.

 

Maybe I'm thinking about this wrong...

I understand the what you're proposing with the adjustment of the end-links (or washer adding if you've got stock parts). BUT... what you're effectively doing is pre-loading the bar in ONE direction. Let's say you add the washers on the right side of the car. You have pre-loaded the bar for left-hand turns. You've made the situation worse for right hand turns.

When you turn right and the suspension begins to move, the very first movement will be to take out that small preload you've put in the bar. Next, you will run into the slop area, caused by the slack in the mountings and links. Finally, you will get into the actual resistance area of the bar itself. Unless you're running Nascar, I don't see the point of this "mod" at all unless you purposely want to preload for one turning direction.

Urethane/delrin or spherical bearing/solid mounts and high quality end-links seem to be the only way to remove this dead area...

**just to clarify, this statement is my thought process and 100% hypothesis, NOT a statement of fact**


[Modified by JeffS, 12:47 PM 3/15/2002]

 

Apparetnly this is to compensate for the weight of the driver, or to correct for any pre-load after installation. Nothing about "dead area."

 

JeffS is wrong. The issue is whether the sway bar has any tension on it at rest with the driver and fuel in the car. Think of the shims as lengthening the end link. The sway bar doesn't know how long the end links are only whether there is any force on it.

The other issue is toe out as a suspension preload. Toe out (or toe in) preloads some suspension bushings when the car is in motion. This translates to slightly faster turn in as the bushings do not have to compress as much before the wheel starts turning.

REgards,
Alan

 

Ah ha! There's hope for me yet! Thanks Alan.

 

And the difference between that and swaybar pre-load is that the preload on a bar will cause different handling in either direction. Turn right, the car might oversteer. Turn left, and the car may understeer. Not exactly what you want at an autocross or road course. Also might explain why my car just does not like turning to the left (Nascar and Lefthook @ VIR)

I really need to re-do the install since I'm positive I installed it with the car in the air and the suspension in full droop

 

Thanks Alan,

"The issue is whether the sway bar has any tension on it at rest with the driver and fuel in the car."

Finally some one who is not talking nonesense, don't know where people dream up some of there ideas!