Impact of swaybar change on suspension settings

RedMisted

RedMisted

New member
Hello all.

I'm just throwing this in here for opinions.

If one changes to larger sway bars on a car equipped with the MacPherson strut-front, live axle-rear suspension, does this automatically mean that alignment settings (camber in particular)and things like tire pressures have to be revisited?

I'm thinking about getting an adjustable front sway bar, am wondering if I am going to have to fool much with alignment/tires/damper compression for each of the sway bar settings... :blink:

Thanks for any help!
 
Chris, This will definitely change the overall balance and handling of the car. The hard part of your question is where did we start, not exact numbers mind you. But how far off were you before.
I would start at your original settings then change ONE thing at a time. Then document your results. Generally, I mean GENERALLY, as bars get bigger, springs get lighter.
Maybe not that much of a change on caster/camber, and air pressure settings. But, when you stiffen a shock to help combat roll, that setting is erased by a bigger bar. Bigger springs that help fight roll in corners are now aided by bigger bars, spring rates may go down, IF, they were correct for a smaller bar setup. There are a few books with some great discussions regarding this. See Carroll Smith ( honestly, you should have all his books), and Ross Bentley, and Racecar Vehicle Dynamics by Millikan and Millikan!!
 
My car leans way too much in the corners. So my thinking is to increase both bars to flatten the car while preserving its current balance, which I like to fine tune with the twist of the front rebound knob.

I was looking at a few dozen pictures of my car taken when I was at VIR last spring. Everybody around me looked relatively flat. I looked like Uncle Mort stealing a lap in his Oldsmobuick.
 
Don't start with bars. You have to get the springs balanced, and the rate right. Do you know what is on the car now?

Your car is probably not TOO different than mine in that you want a 3:2 or 2:1 ratio front to rear. Then, once you get the balance right (which to me means just a tad bit of oversteer but this is personal preference), just go up in rate until you start losing grip (the car slides).

A simple way to do this is at a school parking lot on a Saturday and a makeshift skid pad.

Once you get the springs (which will control roll as well) dialed in, then put the bars on and use them to fine tune.

On a heavyish RWD drive car with a stick axle, you'll want a lot of front bar (helps with rear grip, and works to limit you picking up in the insider rear) and maybe even no rear bar at all (I don't run a rear bar).



RedMisted said:
My car leans way too much in the corners. So my thinking is to increase both bars to flatten the car while preserving its current balance, which I like to fine tune with the twist of the front rebound knob.

I was looking at a few dozen pictures of my car taken when I was at VIR last spring. Everybody around me looked relatively flat. I looked like Uncle Mort stealing a lap in his Oldsmobuick.
Click to expand...
 
JeffYoung said:
Don't start with bars. You have to get the springs balanced, and the rate right. Do you know what is on the car now?

Your car is probably not TOO different than mine in that you want a 3:2 or 2:1 ratio front to rear. Then, once you get the balance right (which to me means just a tad bit of oversteer but this is personal preference), just go up in rate until you start losing grip (the car slides).

Once you get the springs (which will control roll as well) dialed in, then put the bars on and use them to fine tune.

On a heavyish RWD drive car with a stick axle, you'll want a lot of front bar (helps with rear grip, and works to limit you picking up in the insider rear) and maybe even no rear bar at all (I don't run a rear bar).
Click to expand...

My car weighs about 2935 w/ driver. (At least 55% of the weight is over the front, I'd assume.) Spring rates are 900 front and 250 rear with a 27mm solid bar on the front. There is no rear bar.

It was suggested to me that I try a 30mm front bar, and then adjust (if necessary) by adding either a 21mm or 23mm rear bar if the car shows too much understeer. (I actually prefer a car that is slightly loose.)

But it seems sensible to maximize the spring bit first. I always thought that a car was adjusted first with tire pressure/damper/alignment changes, then springs (if necessary), then sway bar changes (if necessary).

On that note, maybe I should forget the bars and go to 1100 lbs. springs in the front and 300 in the rear. Hopefully this won't be too significant a bump in rates. As some of you know, I'm the first of a breed. I don't think the AS Mustangs have much relevancy here.
 
Last edited:
Before bars I would definitely go up to about 500-550 in the rear, maybe even more. That seems way, way too unbalanced. Like Jeff said 2:1 maybe 3:2 front to rear.
One big down side of big bars is that they will cause the inside tires to unweight as the outside tire is put into compression. Especially bad in straight axle car, where the rear wheels make you go!!
I would go out and get a set of 550 springs, thow them on the back and drive the car like Jeff said, autocros, DE, parking lot and see the difference!! You may even find thats not enough.
 
do you know what your corner weights are? not %, actual lbs. i agree that seems like too big of a diff between f/r, but then again i'm guessing there's a lot more weight on the nose of your car compared to my miata.

on a car like this don't you want a little softer springs than normal in the back so it can "sh*t 'n git?"
 
tnord said:
do you know what your corner weights are? not %, actual lbs. i agree that seems like too big of a diff between f/r, but then again i'm guessing there's a lot more weight on the nose of your car compared to my miata.

on a car like this don't you want a little softer springs than normal in the back so it can "sh*t 'n git?"
Click to expand...

The car was corner weighed and the corners cross-adjusted but I couldn't tell you off the top of my head what the weights are.

Older Mustangs are notorious for being nose-heavy. An SN95 Mustang GT had a 58/42 weight distribution when new. Cobras not much better.

As for rear spring rate, I was warned about going much above 200-300 lbs. Must have something to do with a Mustang being a Mustang. Plus, if you look at the AS Mustangs, I believe many of them have softish rear springs. (I could be wrong here.)I do know that their front rates can be as high as 1200 lbs.

I also know that with 900 lbs. springs in the front and 250 in the rear, the balance of my car is toward a bit of oversteer. That's after I adjust for it using the rebound knob. Another half-turn toward full-firm and the car gets uncomfortably nervous.
 
Last edited:
Have you added a Five or Three Link to the rear end? If not, don't add a rear bar! You must first free up the rear end of all of it's bind. Before you do that you have the biggest rear sway bar available, the rear axle. Your spring rates aren't far off for a Mustang. A slightly bigger front bar "might" be in order? Are you ride height adjustable front and rear? Feel free to drop me a line anytime and I'll talk Mustang geometry all day.
 
Rabbit07 said:
Have you added a Five or Three Link to the rear end? If not, don't add a rear bar! You must first free up the rear end of all of it's bind. Before you do that you have the biggest rear sway bar available, the rear axle. Your spring rates aren't far off for a Mustang. A slightly bigger front bar "might" be in order? Are you ride height adjustable front and rear? Feel free to drop me a line anytime and I'll talk Mustang geometry all day.
Click to expand...

I've got an adjustable competition-grade panhard bar on the car. My ride height is adjustable at all corners, and the car is pretty low as it is. I'm pretty reluctant to drop the car even lower at the front, because I have these friggin' wiring harnesses in the upper fenderwells that are in peril from the tires when the car is under heavy lateral load.
 
RedMisted said:
I've got an adjustable competition-grade panhard bar on the car. My ride height is adjustable at all corners, and the car is pretty low as it is. I'm pretty reluctant to drop the car even lower at the front, because I have these friggin' wiring harnesses in the upper fenderwells that are in peril from the tires when the car is under heavy lateral load.
Click to expand...

Don't lower the car! I suspect you may already be too low. A Pan Hard on it's own isn't enough. If you leave the rear control arms alone and add a Pan Hard you actually can make things worse. Your suspension is trying to superimpose one rear roll center over another, ouch!

Run your front ride height so that you can draw a straight line from the lower ball joint center line to the front control arm bushing center line and square that to the earth. Then corner weight from there.
 
Last edited:
To answer the original question - physically installing an different anti-roll bar will not have an affect on existing static alignment settings - assuming correct installation with no suspension preload. It will have a dynamic affect as discussed above.
 
I would tune in this order:

1. Springs
2. Bar
3. Alignment
4. Tire pressures

Chris is right that if you don't have a tri-link, a panhard can actually hurt you. I'd do that before I spent any more money on the suspension.

Without a tri, a softer rear spring will generally help you with grip at the rear end as Travis notes.

With one, you can go up some in spring rate.

Front bar, no rear. Tune on a friction circle to taste, then work on tire pressures to even out tire temps.

RedMisted said:
The car was corner weighed and the corners cross-adjusted but I couldn't tell you off the top of my head what the weights are.

Older Mustangs are notorious for being nose-heavy. An SN95 Mustang GT had a 58/42 weight distribution when new. Cobras not much better.

As for rear spring rate, I was warned about going much above 200-300 lbs. Must have something to do with a Mustang being a Mustang. Plus, if you look at the AS Mustangs, I believe many of them have softish rear springs. (I could be wrong here.)I do know that their front rates can be as high as 1200 lbs.

I also know that with 900 lbs. springs in the front and 250 in the rear, the balance of my car is toward a bit of oversteer. That's after I adjust for it using the rebound knob. Another half-turn toward full-firm and the car gets uncomfortably nervous.
Click to expand...
 
http://corner-carvers.com/forums/index.php

This forum site is heavy into Mustangs. I would suggest that you do a search first and read any posting that pop up first before you post a question. Most likely the question has been asked before and the members there are not friendy to people who post question that have been asked and answered already.
 
jimbbski said:
http://corner-carvers.com/forums/index.php

This forum site is heavy into Mustangs. I would suggest that you do a search first and read any posting that pop up first before you post a question. Most likely the question has been asked before and the members there are not friendy to people who post question that have been asked and answered already.
Click to expand...

Thanks for the link. I'll have a look.

I guess that, like in politics or religion or anything else, I'll form my own philosophy of setting up a car. And my ideas will evolve as I see fit. And then it won't matter what anyone thinks. The only thing that will matter is what happens on the track.
 
Last edited:
sway bars

On a Mustang front end the coil spring is not on the strut so you have to know what the motion ratio is first, then you can figure what spring rate to get to have the correct wheel rate. You cannot just compare springs from one car to another.

I agree that the front spring rates are going to be in the 1100 -1200 lbs range. When you get too much spring, it will push like a dump truck.

Skid pad testing is very helpful to find when it pushes, then back off a little on the springs. This also the time to adjust the camber angles to get tire temps close. Once your close, then fine tune with sway bars.
 
OK. I follow you guys. Thanks to all for the help.

Now, someone please tell me. (I've been sitting here for three hours on this computer trying to find an answer that doesn't seem to exist here in cyberspace.) Why would anyone put a larger sway bar on the front of a car if the spring rates both front and rear have been optimized (for control and balance), w/o including a rear bar in the deal?

Wouldn't that be asking for an understeer situation? I was told "not necessarily."

Can someone explain the physics of this to me? Or are Mustangs subject to some freaky voodoo immune from natural laws?
 
Last edited:
RedMisted said:
OK. I follow you guys. Thanks to all for the help.

Now, someone please tell me. (I've been sitting here for three hours on this computer trying to find an answer that doesn't seem to exist here in cyberspace.) Why would anyone put a larger sway bar on the front of a car if the spring rates both front and rear have been optimized (for control and balance), w/o including a rear bar in the deal?

Wouldn't that be asking for an understeer situation? I was told "not necessarily."

Can someone explain the physics of this to me? Or are Mustangs subject to some freaky voodoo immune from natural laws?
Click to expand...

One thing that comes to mind (I'm not a Mustang guy, so I don't know if this applies specifically) is camber change, or lack thereof. In some cases, a stiffer front bar keeps the front suspension in a sweeter portion of the camber curve as the car rolls on the suspension. The idea being to keep the outside front wheel in a more optimum camber situation for a longer period of the entire cornering process (turn in - max load - track out). More roll stiffness = less roll = less camber change. If this were the case, you would most likely have to adjust camber to take advantage.
 
You must log in or register to reply here.
Back
Top