Re: Ok then: stress bar vs sway bar

["Vee Dubb" <scirious@hotmail.com>]

So here's my two cents on stress and anti-roll/sway bars.  I plan on 
rambling on a bit here, so delete now, or foreveer hold your piece.

"Stress bars": I mor e often call them strut tower braces.  Stiffening the 
chassis helps keep from twisting the car apart because it distributes stress 
at one corner of the car to another.  Might keep a car from cracking or 
bending, but the performance advantage is essentially in keeping things 
where they were designed to be (suspension geometry wise), and by speading 
up repsonse time to steering inputs.  --If there is less springyness in the 
suspension then the car reacts faster to transitions.

So speeding up transitions in nice.  A strut tower brace (stress bar), 
stiffer suspension (shocks and springs that is), or stiffer anti-roll bars 
will all help this.  The strut tower brace seems like a nice place to start 
because they are relatively cheap and might reinforce the car's chassis, 
which is good for hard driving like autocross and such.  blah, blah, blah...

Anti-roll bars make things really interesting.  They can keep a car flatter 
in a turn, but they essentially do this by making each wheel on an axle 
"less independent" from its counterpart on the other side of the car.  The 
important part is that anti-roll bars increase roll resistance. Now, doesn't 
that sound obvious?  Here's the key:  the axle (front or rear) with the most 
roll resistance is generally the one that is going to loose traction first.  
If you want to ask why, I'll tell you, but let's just assume it's true for a 
minute.

So if you put a stiffer roll bar up front, the roll resistence up front 
increases, and you are more likely to experience "understeer".  Increase the 
roll resistance in the back, and oversteer becomes more prevelant.  If you 
don't know what over- and understeer mean, ask me.

Now front engine'd cars might well understeer no matter what you do, right?  
Actually, with a big enough rear anti-roll bar they will be neutral or even 
oversteer about as much as you wish.  Your personal preferences for under or 
oversteer might determine whether you use a bigger front or a bigger rear 
bar to keep you flat.  You can of course add one of each if you like.

Other things you can do which will affect this balance includes messing with 
tire pressure, changing geometry, and swapping out spring s and shocks.

So you aren't likely going to make a radical adjustment to your suspension 
geometry, so we'll ignore that. unless...[see camber comments]

The biggest change you might make to all of this would be do get some new 
shocks and springs.  This will change the spring rates, shock rates and roll 
resistances as well.  The ride height change might mean that you need to 
change the camber of the front wheels to get it back to normal, of course.

The next biggest suspension change, I think, would be to start swapping 
anti-roll bars until the car handles the way you want it to, as mentioned 
above.

Then you can tweek tire pressures to fine tune things further and make  
changes on a daily basis if need be to suit particular track conditions.

Strut tower braces won't really factor into any of this suspension tuning 
noticeably, but they will give better response and maybe prevent you from 
bending or cracking something important.

So here's the advice part:

If you are trying to make a car handle well enough for racing, you might 
eventually do all of this stuff.  Starting with anti-roll bars might be a 
mistake, because after you change the suspension your roll bar might turn 
out to be the wrong one entirely.  If you don't ever plan on changing to 
stiffer shocks and springs, --keeping in mind that the one's you are driving 
on will wear out someday if they haven't already-- then sway bars are a good 
thing. (i.e. don't change sway bars unless you like the shocks and springs 
you have)

A strut tower brace will be a beneficial improvement now, and would be a 
good first step toward future modifications (i.e. would be compatible and 
eventually necessary with whatever you do in the future).

>I'm assuming I donšt really need a stress bar cause I donšt do any >racing 
>or really heavy driving.  Would a sway bar help me with >cornering, and the 
>"body roll" (my term) I feel when cornering or >going over dips/rises in 
>the road at good speed?

If you use a bigger anti-roll bar, you will make the wheels tend to travel 
in the same direction together (i.e. both go up, or both go down).  The 
opposite motion is what happens when the body rolls (one goes up, and the 
other goes down).  Preventing that is how anti-roll bars do their thing.

Now consider hitting a pot hole with one wheel.  If the body of the car 
doesn't move (i.e. if the ride remains comfortable), then only one wheel 
will fall into the hole.  If the two wheels want to move together because of 
your massive anti-roll bar, then the body of the car tends to fall into the 
hole (read - uncomfortable ride with excessive body motion), because the 
wheel can't fall without taking the car with it.

Now what about those "dips and rises" you mentioned?  If both wheels go over 
a dip, they both want to travel together.  That's what the bigger anti-roll 
wants them to do, so it doesn't do anything about it.  What I'm saying is 
that an anti-roll bar won't affect what the car does when both wheels hit a 
dip or a rise in the road at the same time.  To help with that you need 
stiffer shocks and springs (to help the car regain its composure after that 
kind of disturbance).  A strut tower brace will keep the front suspension 
from feeling mushy at times like these, so a strut tower brace is your best 
bet here as well.

The impact of an anti-roll bar will be much greater as far as keeping the 
car flat in turns, so if that is your biggest concern, and if you aren't 
going to swap shocks and springs, then you won't go wrong with an anti-roll 
bar.

If you think you might want to try putting better shocks and springs on the 
car eventually, then go with the strut tower brace now and save up for that 
suspension, which should be the next item on your list. The brace will be 
really necessary then because of the extra stress the stiffer suspension 
brings in.


If you want to do some light reading on the whole suspension tuning subject, 
check out "Performance Handling: Techniques for the '90's" by Don Alexander. 
  It explains this sort of stuff much better and in far more depth than I 
have or could.  I found it at Barnes&Noble, but I'm sure you can get it 
anywhere.

Sincerely;

Brian Haygood
'87 Scirocco 16v
'95 Passat GLX
'00 GTI GLX




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