Impact of swaybar change on suspension settings

[billf]

Only Mustangs? Not necessarily

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

 

[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

 

[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.