School me on FiST sway bars...

[zohaib]

So i've been autocrossing for a long time, but this is my first time with a vehicle which doesn't have an independent rear suspension.

It seems that to make the handling on the FiST more responsive, Ford's engineers used a smaller front sway bar and stiffened the rear torsion beam.

Now, with my "aggressive" driving style, the car gets a little understeery, and on my old FWD cars, I solved that with rear sway bars (and eventually stiffer rear coilover springs) and inducing a little lift-off oversteer.

In the case for a torsion beam, I don't see where the benefits lie in connecting a sway bar strut to strut. Maybe by reducing the overall moment arm? But every sway bar on the market is bent towards the torsion beam so it does't seem like a huge improvement...

It seems like it would be more beneficial to stiffen the torsion beam itself without boxing it, something to the effect of Pierce Motorsports torsion bar?

Or maybe the rear sway bars exist to even out the fatter front sway bars on the market?

What am I missing?

Help me FiSTy forum, you're my only hope.

 

[AnimalMother]

What am I missing?

Help me FiSTy forum, you're my only hope.

You're not missing anything. Its still rsb to help with understeer and rotation. Ive been experimenting with this car since August and I just got it figured out. Ive tried full stock, koni yellow in the rear with and without rsb, koni orange w/stocks spring, orange with ST springs (STX), yellows front and back with ST springs, yellows front and rear with oem springs with and without rsb. Yellow rear with orange front & oem springs with and without rsb. Sheesh!

The best thing I did, besides tires of course, was yellows in the rear at full + (-1/4 turn) with eibach rsb (eibach because it was on sale). If you're aggressive then this is for you. This got me a pax win... 1/97.

If you go ST springs you don't want a rsb... you will have more camber and the rake will help with balance... it will drive flat and require little rotation.

do or do not, there is no try.

 

[Typical_Dodson]

I tried an ST Suspensions RSB on otherwise stock suspension with 200TW tires. Seemed to only make the 3 wheeling worse. It seems that a set of Koni yellows at the rear may cure the dog-legging and allow me to bolt that RSB back on.
I run the Eibach FSB, the biggest of the bunch, because I found it used on this very forum. It has reduced understeer, helps the car corner a bit more flat, and feels much more willing to change directions especially in a slalom.
For SCCA stock, you can add or replace ONE sway bar. For this reason, most HS guys will replace the front sway bar. Some say the Eibach is overkill and prefer the Fiesta SE sway bar, which is actually larger than the ST sway bar. You'd need a sway bar and the mounting hardware if you went that route. I believe the ST Suspensions FSB is the same size as the stock SE bar.

 

[zohaib]

You're not missing anything. Its still rsb to help with understeer and rotation. Ive been experimenting with this car since August and I just got it figured out. Ive tried full stock, koni yellow in the rear with and without rsb, koni orange w/stocks spring, orange with ST springs (STX), yellows front and back with ST springs, yellows front and rear with oem springs with and without rsb. Yellow rear with orange front & oem springs with and without rsb. Sheesh!

The best thing I did, besides tires of course, was yellows in the rear at full + (-1/4 turn) with eibach rsb (eibach because it was on sale). If you're aggressive then this is for you. This got me a pax win... 1/97.

If you go ST springs you don't want a rsb... you will have more camber and the rake will help with balance... it will drive flat and require little rotation.

do or do not, there is no try.

Once I install the STS springs, I'll re-evaluate and see what's necessary. Thank you for your info, I should have joined these forums earlier!

 

[zohaib]

I tried an ST Suspensions RSB on otherwise stock suspension with 200TW tires. Seemed to only make the 3 wheeling worse. It seems that a set of Koni yellows at the rear may cure the dog-legging and allow me to bolt that RSB back on.
I run the Eibach FSB, the biggest of the bunch, because I found it used on this very forum. It has reduced understeer, helps the car corner a bit more flat, and feels much more willing to change directions especially in a slalom.
For SCCA stock, you can add or replace ONE sway bar. For this reason, most HS guys will replace the front sway bar. Some say the Eibach is overkill and prefer the Fiesta SE sway bar, which is actually larger than the ST sway bar. You'd need a sway bar and the mounting hardware if you went that route. I believe the ST Suspensions FSB is the same size as the stock SE bar.

I can see why a thicker (but not too thick) front sway bar would benefit a car with stock springs/bump stops by helping redistribute weight during hard cornering, but that won't necessarily be my case once new springs go in.

I'm already in STX due to my strut bars and chassis bracing, so the first thing I want to do is change the COG and weight distribution by playing with the springs, using a monotube shock to increase dampening reaction time and force, and then re-evaluating body roll accordingly. If I start getting snap oversteer at lift off, I'll consider stiffening the FSB.

 

[BRGT350]

Use left foot braking. It is cheaper than a sway bar and will produce a lot of oversteer and dial out the understeer. I am lost on increasing the front sway bar thickness and reducing understeer. A larger rear bar creates more oversteer by increasing the rear wheel rate. A larger front bar makes the car understeer more by increasing the front wheel rate. On my CP Mustang, I run a very tiny front sway bar to counteract the increased rear traction from a torque arm 3-link rear suspension. I agree with AnimalMonster's comments on what would work. I ran Koni yellow's on full stiff, a large rear bar, and stiffer springs on my Focus. The rear would easily rotate, enough that it spun a few times on me. With my Fiesta, I left the dampers and sway bar/torsion beam alone and changed my braking method. Massive difference in control with limited parts. Of course, I am not including the cost of going to a rally school to learn the technique.

 

[zohaib]

Use left foot braking. It is cheaper than a sway bar and will produce a lot of oversteer and dial out the understeer. I am lost on increasing the front sway bar thickness and reducing understeer. A larger rear bar creates more oversteer by increasing the rear wheel rate. A larger front bar makes the car understeer more by increasing the front wheel rate. On my CP Mustang, I run a very tiny front sway bar to counteract the increased rear traction from a torque arm 3-link rear suspension. I agree with AnimalMonster's comments on what would work. I ran Koni yellow's on full stiff, a large rear bar, and stiffer springs on my Focus. The rear would easily rotate, enough that it spun a few times on me. With my Fiesta, I left the dampers and sway bar/torsion beam alone and changed my braking method. Massive difference in control with limited parts. Of course, I am not including the cost of going to a rally school to learn the technique.

I already left foot brake

A sway bar works by redistributing the forces from one side of a car to another, reducing both sway and dive. There is a fine balance; you want a sway bar that's thick enough to transfer the weight from one side to the next, but it can't be so thick where it starts to hinder the independent movement of the two sides. Generally speaking, a thicker front sway bar on a FWD car will induce understeer, but if designed right, the balanced weight transfer will help the car stay more planted, as reported by Typical_Dodson. A lot of it will boil down to driving style and reaction time as well, so everyone will have a varied experience.

 

[BRGT350]

nice to find another LFB'er out there! It was one of the best improvements I made to driving. As for how a sway bar works, I am very familiar with them as I was a suspension engineer for a few years working with both front steer and rear drive suspensions. You are totally right that a lot of this comes down to driving style. Another option to decrease rear grip for better rotation is going to a skinnier rear tire and greatly increasing the rear tire pressure. The increased rear tire pressure will increase the wheel rate and a smaller contact patch will reduce the surface area of the tire on the ground. I used to see a lot of guys doing that with FWD cars years ago, but not so much anymore. I think the local autocross group has changed from really die hard racers to guys who just go out to have fun with their street cars. I only get out once or twice a year anymore, so not enough to really be competitive anymore.

 

[Joker328]

I'm not sure why, when you already don't have an independent rear suspension, you would want to make the coupling between the rear wheels even greater. The FiST is already pretty easily unsettled when you hit a bump with one wheel in a corner. With a torsion beam like this, hitting a bump on one wheel can affect the toe and camber of both wheels. For example, if you catch the inside curbing on a corner, you could end up with a rapid shift to positive camber on the outside wheel. Yes, that would give you oversteer, but it is is reducing your overall traction, and if it came on suddenly, could lead to snap oversteer. I would think adding a sway bar or stiffening the torsion beam would increase this effect. If you are looking to reduce body roll and reduce understeer, I would think stiffer rear springs with a bit lower ride height would be preferable (all else equal). And of course, at Bryan pointed out, technique will probably have a bigger impact on lap times than any of these mods.

 

[AnimalMother]

Once I install the STS springs, I'll re-evaluate and see what's necessary. Thank you for your info, I should have joined these forums earlier!

Sure thing. Disclaimer: this is all in regards to autocross... sorry. I get my info from trial and error and taking into account what the very fastest drivers say and use, not forum consensus. I don't know how to set up a commuter car.

 

[zohaib]

nice to find another LFB'er out there! It was one of the best improvements I made to driving. As for how a sway bar works, I am very familiar with them as I was a suspension engineer for a few years working with both front steer and rear drive suspensions. You are totally right that a lot of this comes down to driving style. Another option to decrease rear grip for better rotation is going to a skinnier rear tire and greatly increasing the rear tire pressure. The increased rear tire pressure will increase the wheel rate and a smaller contact patch will reduce the surface area of the tire on the ground. I used to see a lot of guys doing that with FWD cars years ago, but not so much anymore. I think the local autocross group has changed from really die hard racers to guys who just go out to have fun with their street cars. I only get out once or twice a year anymore, so not enough to really be competitive anymore.

So I've been bumping up the rear pressure close to 40psi to get it to rotate; anything higher I was getting squirreley with the stock tires. Maybe a higher psi once I switch to grippier tires?

I totally agree on using a skinnier tire, but that's not cost effective for me. I'm actually afraid of going to 215's all around for that reason - I don't want to over-grip the rear. It's a huge balancing act between competition, budge, and practicality. Thank you for your input!

 

[zohaib]

I'm not sure why, when you already don't have an independent rear suspension, you would want to make the coupling between the rear wheels even greater. The FiST is already pretty easily unsettled when you hit a bump with one wheel in a corner. With a torsion beam like this, hitting a bump on one wheel can affect the toe and camber of both wheels. For example, if you catch the inside curbing on a corner, you could end up with a rapid shift to positive camber on the outside wheel. Yes, that would give you oversteer, but it is is reducing your overall traction, and if it came on suddenly, could lead to snap oversteer. I would think adding a sway bar or stiffening the torsion beam would increase this effect. If you are looking to reduce body roll and reduce understeer, I would think stiffer rear springs with a bit lower ride height would be preferable (all else equal). And of course, at Bryan pointed out, technique will probably have a bigger impact on lap times than any of these mods.

After the conversation in this thread, I'm inclined to agree with you. I'll install the ST springs in the coming weekend and test it out soon after. I will let you know what I think!

 

[zohaib]

Sure thing. Disclaimer: this is all in regards to autocross... sorry. I get my info from trial and error and taking into account what the very fastest drivers say and use, not forum consensus. I don't know how to set up a commuter car.

I've been "tuning" cars for years, this is just my first time with a torsion beam. A lot of what I need to do will be trial and error, but at least with this discussion I know the trial and error of others, and don't have to necessarily repeat those errors

As for commuter car, I'll just have to suck up the harshness, hah.

 

[M-Sport fan]

You're not missing anything. Its still rsb to help with understeer and rotation. Ive been experimenting with this car since August and I just got it figured out. Ive tried full stock, koni yellow in the rear with and without rsb, koni orange w/stocks spring, orange with ST springs (STX), yellows front and back with ST springs, yellows front and rear with oem springs with and without rsb. Yellow rear with orange front & oem springs with and without rsb. Sheesh!

The best thing I did, besides tires of course, was yellows in the rear at full + (-1/4 turn) with eibach rsb (eibach because it was on sale). If you're aggressive then this is for you. This got me a pax win... 1/97.

If you go ST springs you don't want a rsb... you will have more camber and the rake will help with balance... it will drive flat and require little rotation.

do or do not, there is no try.

When you had that PAX win, what was the FRONT setup on the car?

 

[BRGT350]

So I've been bumping up the rear pressure close to 40psi to get it to rotate; anything higher I was getting squirreley with the stock tires. Maybe a higher psi once I switch to grippier tires?

I totally agree on using a skinnier tire, but that's not cost effective for me. I'm actually afraid of going to 215's all around for that reason - I don't want to over-grip the rear. It's a huge balancing act between competition, budge, and practicality. Thank you for your input!

the two different tire thing never worked for my budget either. I think I used to run 45psi in the rear on my Focus when I was really trying to get it to rotate. I would put the rear shocks at full stiff, had a different rear sway bar (not the biggest since they would break control arms), and up the tire pressure. I would bleed hot air off after the runs to keep the pressure at 45. I run 215 on all 4 corners on the ST and find it ok, but again, getting out to one or two autocrosses a season doesn't make me competitive enough for it to make a difference. I also switch between my Mustang and Fiesta, so I have to change my driving style between cars. I just go to have fun and be happy to be out on course.

 

[AnimalMother]

When you had that PAX win, what was the FRONT setup on the car?

Front... Stock.

In the rear, Koni yellow full positive, with an eibach rsb. (The yellows also help with braking and rear squirm while braking)

All 4 tires equal pressure ~35psi.

This is the setup I was advised to use initially. However, I'm stubborn and like to figure things out for myself (i also tried stock wheels, 16x7 and 16x7.5 in stx, and 3 different tires this year). So after trying all of those other configurations and throwing away a bunch of time and money, ive arrived back where i started.

 

[M-Sport fan]

Front... Stock.

In the rear, Koni yellow full positive, with an eibach rsb. (The yellows also help with braking and rear squirm while braking)

All 4 tires equal pressure ~35psi.

This is the setup I was advised to use initially. However, I'm stubborn and like to figure things out for myself (i also tried stock wheels, 16x7 and 16x7.5 in stx, and 3 different tires this year). So after trying all of those other configurations and throwing away a bunch of time and money, ive arrived back where i started.

THANKS!

I guess my next expenditure on the car will be the rear Sports, which I was planning to do anyway.

When I spoke to Koni product development about a month ago, they did tell me that the ST specific (with ALL of the correct fittings/seats/etc., and with a stiffer valving range than the standard Fiesta's) FRONT Sports ARE planned to eventually go into production.

But, just like everything else it seems, our app must take a back seat to all of the other newly released rides out there, which they (just like every other aftermarket manufacturer out there does) 'leapfrog' ahead of OUR platform for product releases due to them being more 'popular'.

 

[zohaib]

Front... Stock.

In the rear, Koni yellow full positive, with an eibach rsb. (The yellows also help with braking and rear squirm while braking)

All 4 tires equal pressure ~35psi.

This is the setup I was advised to use initially. However, I'm stubborn and like to figure things out for myself (i also tried stock wheels, 16x7 and 16x7.5 in stx, and 3 different tires this year). So after trying all of those other configurations and throwing away a bunch of time and money, ive arrived back where i started.

This backs up one of my earlier implied statements, that it's more beneficial to work the rear suspension to increase rotation rather than the front. Good to know!

 

[Typical_Dodson]

I can see why a thicker (but not too thick) front sway bar would benefit a car with stock springs/bump stops by helping redistribute weight during hard cornering, but that won't necessarily be my case once new springs go in.

I'm already in STX due to my strut bars and chassis bracing, so the first thing I want to do is change the COG and weight distribution by playing with the springs, using a monotube shock to increase dampening reaction time and force, and then re-evaluating body roll accordingly. If I start getting snap oversteer at lift off, I'll consider stiffening the FSB.

Obviously, the sway bars would be the last component we SHOULD change when tuning suspension, but with SCCA's rules I can't mess with springs at all. There are very limited damper options for this car outside of coilovers as well. If you're already in STX I can see your logic in getting the springs and dampers squared away before deciding on a sway bar.

If it makes any difference, the Mazda2 rear suspension setup is identical, although I doubt the Mazda2 aftermarket is as good as ours.

 

[ThaiFiesta]

If it makes any difference, the Mazda2 rear suspension setup is identical, although I doubt the Mazda2 aftermarket is as good as ours.

The Mazda 2 uses the torsion beam of the stock Fiesta. Mounting holes are slightly different.
The newest Mazda 2 with rear discs (mounted inboard) may be a modified ST torsion bar - Mazda has not been able to confirm