Impact of swaybar change on suspension settings

[RedMisted]

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!

[DoubleXL240Z]

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!!

[RedMisted]

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.

[CRallo]

Spring rate? Car weight?

[JeffYoung]

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).




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.

[RedMisted]

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).

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.

[DoubleXL240Z]

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.

[tnord]

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?"

[RedMisted]

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?"

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.

[Rabbit07]

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.

[RedMisted]

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.

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.

[tnord]

of everyone in this thread, i'd listen to chris on this issue.

[Rabbit07]

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.

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.

[betamotorsports]

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.

[JeffYoung]

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.


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.

[jimbbski]

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.

[RedMisted]

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.

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.

[racer240sx]

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.

[RedMisted]

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?

[Gary L]

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?

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.

[billf]

First, Kudos to someone for actually mentioning that the use of Watts or Panhard will confuse the Roll Centers of a Mustang. Don't see that mentioned very often, on any site.

Chris, if I could chime in here to offer an observation: The best front suspension for a Mustang would be a solid axle (ox Cart) to keep the camber of the tire on the pavement, constant while cornering. Such is difficult to achieve with a Mustang, since the camber curve reverses when the lower arm passes horizontal (pointed upwards toward the wheel). The car in stock form begins with the lower arm very close to horizontal, so any lowering attempt will degrade the camber curve. This might be the defining difference between the strut of the Mustang, and other strut cars...they might start with the lower arm angled differently. Differing Center of Gravity heights (Mustang vs smaller cars) will also effect how much a given chassis will roll relative to others in the group.

I believe our best reference is the AS cars...same chassis, with improvements intended to accomplish the same result.

High AS front spring rates serve to keep the chassis as roll-free as possible, using rates of 1000-1200 lb/in (remember the drastic reduction at the wheel from the mid-arm mounting point). Actual wheel rate isn't important here...only that those rates will keep the chassis relatively level and minimize the camber loss at the pavement. Extrapolation from AS to ITR is touchy. We are in uncharted water, here...V8 vs V6 front end weights, 3200 vs what ever we can end up with????

Anti-sway bars povide a method of tuning, and, increasing the roll resistance without increasing the effective wheel rate (in a straight line), so the wheels might stay on the ground.

My thoughts for you, and me...mine is coming along nicely, thank you...is to concentrate on the spring rate first, then try the chassis to see what bar it needs to trim the handling. Observation of the roll angle is important, but try to discern the angle of the lower arm when cornering, too. I'm expecting to begin with 850-950 to start with. Rears are going to be soft with the conflicting Roll Centers (rear), and the presence of the dredded rubber-bushing-bind in the rear...which will lessen with the leveling of the chassis, incidentally.

Keep up the bench engineering!!

Good racing,

Bill:024:

[Rabbit07]

I am going to throw my hat back in the ring here. To answer the front sway bar question you must first answer where the under steer occurs? If you soften the front end the car will turn in better, “less turn in under steer”. It will likely under steer from the apex out, “Corner Exit Under steer”. If you add more bar to the front the opposite will occur. This is due to roll angle and camber loss as stated above.

In regards to the Pan hard or Watts Link. I am a fan of the Steeda Five link for simplicity sake. This will help eliminate the rear suspension bind and allow proper lateral location of the axle. You also gain the ability to raise or lower the rear roll center height. This adds just one more tuning tool. With Mustangs I have found that you first dial in the; Springs rates, front bar size, alignment and shocks. You then tune with rear roll center height, rear roll steer, and sway bars.

[Andy Bettencourt]

To answer the front sway bar question you must first answer where the under steer occurs?

Bingo. More info needed.

[RedMisted]

First, Kudos to someone for actually mentioning that the use of Watts or Panhard will confuse the Roll Centers of a Mustang. Don't see that mentioned very often, on any site.

Chris, if I could chime in here to offer an observation: The best front suspension for a Mustang would be a solid axle (ox Cart) to keep the camber of the tire on the pavement, constant while cornering. Such is difficult to achieve with a Mustang, since the camber curve reverses when the lower arm passes horizontal (pointed upwards toward the wheel). The car in stock form begins with the lower arm very close to horizontal, so any lowering attempt will degrade the camber curve. This might be the defining difference between the strut of the Mustang, and other strut cars...they might start with the lower arm angled differently.

Bill: The use of a rear axle locating device and its problems relative to roll center was something I was researching. What I've gathered is that a Panhard is bad ONLY if paired with aftermarket upper control arms that use spherical components. And that if you use such aftermarket pieces then you must undertake other measures, such as installing a torque arm. But we don't have to worry about torque arms and aftermarket UCAs because they aren't permitted in IT.

As for my own experiences with the panhard, it really didn't make the car handle better (honest), just easier to control under hard cornering. And I've never noticed any unusual stress points under the rear of the car.

Seriously, will lowering a Mustang, on the whole, be detrimental to its handling? There are always trade-offs with anything you do to a car. But, IMHO, the benefits of lowering must outweigh the costs, at least to a point.

On the other hand, if memory serves me correct, I have noticed that some AS Mustangs look a bit on the high side in ride height. This may have something to do with what you're talking about.

[JeffYoung]

Torque arms -- in fact pretty much any additional suspension arm in the rear -- are permitted in IT as a traction bar.

[CRallo]

Seriously, will lowering a Mustang, on the whole, be detrimental to its handling? There are always trade-offs with anything you do to a car. But, IMHO, the benefits of lowering must outweigh the costs, at least to a point.

On the other hand, if memory serves me correct, I have noticed that some AS Mustangs look a bit on the high side in ride height. This may have something to do with what you're talking about.

everyone loves to slam a car, but a lower CG actually takes a back seat to roll center and the coresponding effect on suspension geometery as the suspension moves through its range of motion.

to answer your orginal question based on my experience: changing swaybars may nessecitate a change in suspension settings due to the vehicle rolling differently in corners, but using an adjustable bar to fine tune at the track shouldn't require other changes... ntm at this level of fine tuning, you shouldn't change more than one thing at a time!

and always make sure you're not bottoming your shocks out or hitting your bump stops!!! the car does funny things when the spring rate goes towards infinite!!!!!!

[RedMisted]

I am going to throw my hat back in the ring here. To answer the front sway bar question you must first answer where the under steer occurs? If you soften the front end the car will turn in better, “less turn in under steer”. It will likely under steer from the apex out, “Corner Exit Under steer”. If you add more bar to the front the opposite will occur. This is due to roll angle and camber loss as stated above.

Chris:

First, thanks for your help here.

To answer your question the best I can, it seems that the car, in its current guise, turns in well but may be pushing some on corner exit. This is something I will have to look for next time I'm on track. But when I do blow a corner, it's almost never from missing an apex, but rather tracking out too wide. Hmmm. Could be onto something here...

[Rabbit07]

What I've gathered is that a Panhard is bad ONLY if paired with aftermarket upper control arms that use spherical components. And that if you use such aftermarket pieces then you must undertake other measures, such as installing a torque arm. But we don't have to worry about torque arms and aftermarket UCAs because they aren't permitted in IT. .

Wrong on all accounts! There is still bind in the factory system. Torque arms are traction bars which are allowed in IT

[Rabbit07]

Seriously, will lowering a Mustang, on the whole, be detrimental to its handling? There are always trade-offs with anything you do to a car. But, IMHO, the benefits of lowering must outweigh the costs, at least to a point.

.

Also wrong, you want to reduce the roll moment which will improve the handling.

The Roll Moment is the distance between roll center and center of gravity.

[Z3_GoCar]

Seriously, will lowering a Mustang, on the whole, be detrimental to its handling? There are always trade-offs with anything you do to a car. But, IMHO, the benefits of lowering must outweigh the costs, at least to a point.

On the other hand, if memory serves me correct, I have noticed that some AS Mustangs look a bit on the high side in ride height. This may have something to do with what you're talking about.

Yes, lowering any strut based car too much will have a detrimental effect on the handeling. Once the lower control arm goes past horizontal the front roll center will be below the ground, and as was previously mentioned the camber curve will be going in the wrong direction. There's two options to correct this that are IT legal, raise the the chassis, or make it stiffer. Only one will work better than the other....

One additional thought, you'd also need to know how the roll center changes with roll angle too

[RedMisted]

Yes, lowering any strut based car too much will have a detrimental effect on the handeling. Once the lower control arm goes past horizontal the front roll center will be below the ground, and as was previously mentioned the camber curve will be going in the wrong direction. There's two options to correct this that are IT legal, raise the the chassis, or make it stiffer. Only one will work better than the other....

Wow. I'm really getting an education from everybody on the CG topic.

I stand corrected on the legality of a torque arm in IT.

Still lots to be learned here about what's been discussed. What makes it troubling for me is that I'm the first ITR V6 Mustang, with no real body of work to refer to. I'm not sure as to how relevant the AS cars are to mine. As BillF said, comparing AS to ITR is a "touchy" proposition.

[Andy Bettencourt]

In looking at the AS National results, I inquired as to why such dominance by 2 or 3 guys. Answer? Those guys are the only ones who have figured out how to make them REALLY handle.

Call Andy M. and see if you can get some info/buy some parts.

[billf]

Bill: The use of a rear axle locating device and its problems relative to roll center was something I was researching. What I've gathered is that a Panhard is bad ONLY if paired with aftermarket upper control arms that use spherical components. And that if you use such aftermarket pieces then you must undertake other measures, such as installing a torque arm. But we don't have to worry about torque arms and aftermarket UCAs because they aren't permitted in IT.

As for my own experiences with the panhard, it really didn't make the car handle better (honest), just easier to control under hard cornering. And I've never noticed any unusual stress points under the rear of the car.

Seriously, will lowering a Mustang, on the whole, be detrimental to its handling? There are always trade-offs with anything you do to a car. But, IMHO, the benefits of lowering must outweigh the costs, at least to a point.

On the other hand, if memory serves me correct, I have noticed that some AS Mustangs look a bit on the high side in ride height. This may have something to do with what you're talking about.


Chris,

I disagree with the bold part of your statement (see quote above). Aftermarket upper arms don't change geometry, they just remove some of the bind of the original rubber bushings.

The point I was trying to make is that to add a Panhard, or Watts, or any other type of lateral locating device, will create a new, and different Roll Center for the rear axle. The difficulty is, the Fox/SN95 already have a factory installed Roll Center, created by the two upper arms. The RC is virtual, where the two planes created by the upper arms converge above and behind the center of the housing. If the upper arms are functional (no air bushings), and the Panhard/Watts is added, two Roll Centers will exist, and compete for control when the chassis is in a cornering mode. This will be the increased bind that I referred to in an earlier post. The bind will create new, exponentially increasing spring rates, and we know what can happen when the rates approach infinity. Only now, they will get there faster.

The only way to eliminate the problem is to remove the original geometry, leaving the Panhard/Watts to provide the Roll Center. This will demand that you replace the longitudinal location (have to remove the stock upper arms, or use air bushings) to control axle rotation during acceloration/braking.

We are allowed the Torque Arm as stated above. However, none is made or offered that will fit the only legal rear axle assembly...7.5inch. They are all made for 8.8 inch, and that is what is used on the AS cars. The 8.8 is configured differently, and it makes the torque arm a bolt in/on. If you want a Torque Arm for the 7.5, you have to fabricate one. Three link work well, but you have to find one to clear the required stock upper arms in their original locations. This technology (?) is known, but not easily transferred to the V6 configuration.

Sorry to drag on fellows. One of my favorite topics.

Good racing.

Bill:024:

[RedMisted]

The point I was trying to make is that to add a Panhard, or Watts, or any other type of lateral locating device, will create a new, and different Roll Center for the rear axle. The difficulty is, the Fox/SN95 already have a factory installed Roll Center, created by the two upper arms. The RC is virtual, where the two planes created by the upper arms converge above and behind the center of the housing. If the upper arms are functional (no air bushings), and the Panhard/Watts is added, two Roll Centers will exist, and compete for control when the chassis is in a cornering mode. This will be the increased bind that I referred to in an earlier post. The bind will create new, exponentially increasing spring rates, and we know what can happen when the rates approach infinity. Only now, they will get there faster.

The only way to eliminate the problem is to remove the original geometry, leaving the Panhard/Watts to provide the Roll Center. This will demand that you replace the longitudinal location (have to remove the stock upper arms, or use air bushings) to control axle rotation during acceloration/braking.

Whatever. This gets more complicated by the hour. Now I don't know what to do next with this car. I've never experienced rear bind. Or maybe I don't know what that is. Or perhaps the car's got something going for it... Hmmm.

Comments on how much my car rolls and needs monster bars... Then I see pics of McDermid in his championship Mustang, rolling over like a drunk in a ditch. Comments that my spring rates are too low, should be more in line with the AS cars... Then I remember that my car weighs several hundred pounds less than AS.

New breed problems...

I think I'll just shelve the suspension ideas for a later date. Spend $$$ on sure-fire improvements, such as power and weight reduction.

[jimbbski]

IF you go with a PH bar you can do the poor mans 3-link. That is remove the bushings from both upper arms and replace one with foam rubber and one an aftermarket bushing. The bushings in the axel are hard to replace but you only have to remove one of them and replace with foam rubber to match the upper with the foam bushing. The other should remain stock as it has some "give" required to make this work.
The upper to modify or gut is the one on the side away from where the PHB attaches to the axel.

I did this on my "R" model and it worked well. Is a torque arm better? Yes, but this is easy to do especially under the rule set you have to race under. AS had this problem as well when it started out but rule changes over the years has allowed many more changes then you are.