The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Which rear sway bar?

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Stock 350R rear sway to my knowledge. Quick maths with a 600/800 spring setup you have ~ over 70% front RC (lots of understeer) A large rear bar will tune that out, depending on how big it is you might get around 10% more rear RC (adding oversteer). You need to decide on what springs you will be running first since they are the main provider of roll resistance, then get your damping figured out, lastly tune with sway bars.
 
Stock 350R rear sway to my knowledge. Quick maths with a 600/800 spring setup you have ~ over 70% front RC (lots of understeer) A large rear bar will tune that out, depending on how big it is you might get around 10% more rear RC (adding oversteer). You need to decide on what springs you will be running first since they are the main provider of roll resistance, then get your damping figured out, lastly tune with sway bars.

Thanks for the reply!

RC? (Sorry i'm french canadian)

So keep in mind my car is an ecoboost (ligher). I had 600f and 750R spring rates. I felt like the car had very little weight transfer, I just got 500F and 650R, you think it's going too low? I have not tried the setup yet. I generally prefer a softer car to be able to go over speed bumps etc and try to tune out the roll with sway bars. I dont have 4 way adjust shocks yet.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Thanks for the reply!

RC? (Sorry i'm french canadian)

So keep in mind my car is an ecoboost (ligher). I had 600f and 750R spring rates. I felt like the car had very little weight transfer, I just got 500F and 650R, you think it's going too low? I have not tried the setup yet. I generally prefer a softer car to be able to go over speed bumps etc and try to tune out the roll with sway bars. I dont have 4 way adjust shocks yet.

RC= roll couple:
Roll couple percentage is a simplified method of describing lateral load transfer distribution front to rear, and subsequently handling balance. It is the effective wheel rate, in roll, of each axle of the vehicle as a ratio of the vehicle's total roll rate. It is commonly adjusted through the use of anti-roll bars, but can also be changed through the use of different springs.

I'm guessing here because I don't know the distance between the springs for the ecoboost but its front track width is 152cm and the rear is 165cm so your 500/650 is about 70% front (without taking ARB into consideration) So you'd need to drop the front springs to 400, or some combination of 401-499lbs with a larger rear ARB.
 
RC= roll couple:
Roll couple percentage is a simplified method of describing lateral load transfer distribution front to rear, and subsequently handling balance. It is the effective wheel rate, in roll, of each axle of the vehicle as a ratio of the vehicle's total roll rate. It is commonly adjusted through the use of anti-roll bars, but can also be changed through the use of different springs.

I'm guessing here because I don't know the distance between the springs for the ecoboost but its front track width is 152cm and the rear is 165cm so your 500/650 is about 70% front (without taking ARB into consideration) So you'd need to drop the front springs to 400, or some combination of 401-499lbs with a larger rear ARB.

WOW!
 
343
300
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
Thanks for the reply!

RC? (Sorry i'm french canadian)

So keep in mind my car is an ecoboost (ligher). I had 600f and 750R spring rates. I felt like the car had very little weight transfer, I just got 500F and 650R, you think it's going too low? I have not tried the setup yet. I generally prefer a softer car to be able to go over speed bumps etc and try to tune out the roll with sway bars. I dont have 4 way adjust shocks yet.

Or just go 500F 900R and call it a day :? I assume your rear springs are in the divorced rear spring location.
 
I'm using GT350R bars though with just steeda springs on my OEM PP shocks. The setup was fairly neutral, got rid of most of the understeer the car had prior. However, I Just picked up a set of coilovers with 450/550 springs so will give you some feedback on how the bars feel with the new suspension soon.

One thing I really like about the GT350R bars (other than being dirt cheap) is that the front does not have the bonded bushings. The bonded bushings are awful.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Or just go 500F 900R and call it a day :? I assume your rear springs are in the divorced rear spring location.
With the OE shock/ coilover MR that is 2.4hz front and 2.1hz rear, giving a LOT to pitch and front roll stiffness (more understeer)

I would run 400 front 750-800 rear unless he has lots of aero.
 
343
300
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
With the OE shock/ coilover MR that is 2.4hz front and 2.1hz rear, giving a LOT to pitch and front roll stiffness (more understeer)

I would run 400 front 750-800 rear unless he has lots of aero.
I learn from Kenny Brown he is suggesting 650/1200 for track focused builds for the S550 because when you have more spring rate in the front the Mustang turns faster and this is more important than setting the front mid corner which you can do with trail braking anyway.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
I learn from Kenny Brown he is suggesting 650/1200 for track focused builds for the S550 because when you have more spring rate in the front the Mustang turns faster and this is more important than setting the front mid corner which you can do with trail braking anyway.
While I am no expert, simple statements like "higher front spring rate makes car turn better" is not meaningful in this conversation. If you add roll stiffness to one end of the car, you are reducing total available mechanical grip. If you have predominately aerodynamic grip then you need to run higher spring rates because of the added weight in down force. Where you sacrifice mechanical grip as the more aero you can use effectively the faster your lap time will be.

Does JUST adding front spring make the car turn better? No it does not, if anything it transfers more weight away from the front of the car under acceleration and causes understeer. If you do not have a large amount of aerodynamic grip, you need to pay attention to the rest of the suspension setup (some options are restricted by class, division, or series). What your statement is relevant to here is drivers (myself included) like the feel of an over dampened roll mode and a lot of that is accomplished in the low speed compression settings on the shocks/ dampers. The lower your spring rate, the less rebound bias you are stuck running, and so you can run more compression, this gives the driver the supported feel at turn in.

What we should be focusing on is the roll couple as I mentioned prior. That number is made with just the spring force and does not take into account the ARB. This allows you to select the stiffness of your ARB's. The general rule of thumb is you want low speed oversteer (slight) and high speed understeer (slight). In all the US/OS balance of the car is a driver preference. From my own research and observation drivers start with 55-60% front roll couple and tweak from there. Everyone will always tell you to run as little ARB as you can get away with, as the stiffer it gets the less independent your suspension becomes, if you start lifting a tire you will be slower than the guy who keeps all 4 on the floor.
 
343
300
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
While I am no expert, simple statements like "higher front spring rate makes car turn better" is not meaningful in this conversation. If you add roll stiffness to one end of the car, you are reducing total available mechanical grip. If you have predominately aerodynamic grip then you need to run higher spring rates because of the added weight in down force. Where you sacrifice mechanical grip as the more aero you can use effectively the faster your lap time will be.

Does JUST adding front spring make the car turn better? No it does not, if anything it transfers more weight away from the front of the car under acceleration and causes understeer. If you do not have a large amount of aerodynamic grip, you need to pay attention to the rest of the suspension setup (some options are restricted by class, division, or series). What your statement is relevant to here is drivers (myself included) like the feel of an over dampened roll mode and a lot of that is accomplished in the low speed compression settings on the shocks/ dampers. The lower your spring rate, the less rebound bias you are stuck running, and so you can run more compression, this gives the driver the supported feel at turn in.

What we should be focusing on is the roll couple as I mentioned prior. That number is made with just the spring force and does not take into account the ARB. This allows you to select the stiffness of your ARB's. The general rule of thumb is you want low speed oversteer (slight) and high speed understeer (slight). In all the US/OS balance of the car is a driver preference. From my own research and observation drivers start with 55-60% front roll couple and tweak from there. Everyone will always tell you to run as little ARB as you can get away with, as the stiffer it gets the less independent your suspension becomes, if you start lifting a tire you will be slower than the guy who keeps all 4 on the floor.

What you don't understand here is that you assume that the Mustang out of the factory comes with correct springs and shocks. Adding more shock and spring to a 3800 lbs car is going to help the weight transfer much more than you think. The consensus around where I'm is that my S550 PP OEM suspension setup is and I quote "too soft". Granted my friends are used to drive 3 series BMW's for a leaving and one is even racing M4's in VLN and finished 2nd overall in 2020. So what all of my friends are saying is that more springs/shocks will help the car be more optimal. I added Front ARB and the car is turning better (same as adding more front spring) and lifting whey less the inner front tire. Also to consider here is the GT4 Mustang often running between 800 and 1000 lbs front spring. As I said strictly track speaking yes more front spring help's the front turn. In order for you to benefit from this you want as soft rear as possible without oversteering mid corner. Why ? Because you want to lay down 100% throttle as soon as possible down that straight so Soft rear/Hard Front is the receipt for this PB's with a Mustang.
 
343
300
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
Oh an E peen measuring contest. I do not agree with anything you have said. That's fine.

It's you own right.
I'm just saying that the Mustang is under sprung from factory. I plan to go with Ohlins R&T this season with 500F and 800R in the OEM location. Plan to use the GT PP rear bar for time been but probably will change bushings to some aftermarket option. I discovered that when you add front bar (Steeda on the softest setting) and change alignment (F: -1.4 camber -0.1 toe out per side -0.2 toe out total, R: -1.4 camber +0.1 toe in per side 0.2 toe in total) the car balance moved from Understeer from the factory to Neutral on the OEM PP tires and to slide oversteer in the 275/35/19's I run on the track. But the flex on the rear bar cause the bushings to unglue themselfs. I guess with more spring this thing with the bushings will not happen but aftermarket solution could and should be considered however the OEM bushings are super cheap and easy to replace so it make sense to stuck with it. If when I add the Coilovers I have problem with car balance I would consider adding Steeda adjustable rear swaybar. But Kenny Brown (I did his Speed Therapy Academy) suggest that for the track the car don't need rear bar because every time he added adjustable rear bar to an S550 he just leave it in full soft anyway. With that in mind the reason why the GT350 and GT500 have bigger rear bars is for the added aero from the rear wing (you need more spring rate and bar to prevent load because of downforce) but also this have better bushings. I was surprised when my car balance changed that much because it didn't made sense based on all I had read regarding car setup. My BMW track friends also said that this didn't make sense to them but it's clear that is working. My lap times dropped 5 seconds season beginning to season end (2KM track) just by adding 275/35 stickier tires, Camber Plates, Strut Tower Brace and Front Sway bar and I'm within 1.7 seconds of the 2nd placed VLN driver. I have no doubt that adding more front spring will improve my times even more based on everything posted in this forum. Hope this helps.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
It's you own right.
I'm just saying that the Mustang is under sprung from factory. I plan to go with Ohlins R&T this season with 500F and 800R in the OEM location. Plan to use the GT PP rear bar for time been but probably will change bushings to some aftermarket option. I discovered that when you add front bar (Steeda on the softest setting) and change alignment (F: -1.4 camber -0.1 toe out per side -0.2 toe out total, R: -1.4 camber +0.1 toe in per side 0.2 toe in total) the car balance moved from Understeer from the factory to Neutral on the OEM PP tires and to slide oversteer in the 275/35/19's I run on the track. But the flex on the rear bar cause the bushings to unglue themselfs. I guess with more spring this thing with the bushings will not happen but aftermarket solution could and should be considered however the OEM bushings are super cheap and easy to replace so it make sense to stuck with it. If when I add the Coilovers I have problem with car balance I would consider adding Steeda adjustable rear swaybar. But Kenny Brown (I did his Speed Therapy Academy) suggest that for the track the car don't need rear bar because every time he added adjustable rear bar to an S550 he just leave it in full soft anyway. With that in mind the reason why the GT350 and GT500 have bigger rear bars is for the added aero from the rear wing (you need more spring rate and bar to prevent load because of downforce) but also this have better bushings. I was surprised when my car balance changed that much because it didn't made sense based on all I had read regarding car setup. My BMW track friends also said that this didn't make sense to them but it's clear that is working. My lap times dropped 5 seconds season beginning to season end (2KM track) just by adding 275/35 stickier tires, Camber Plates, Strut Tower Brace and Front Sway bar and I'm within 1.7 seconds of the 2nd placed VLN driver. I have no doubt that adding more front spring will improve my times even more based on everything posted in this forum. Hope this helps.

Yes almost if not every non factory race car is under sprung and under dampened for comfort and safety. If you add front ARB to the car as is which already has terminal understeer you will have more understeer. Springs provide the largest amount of roll resistance and you increase spring rate so as to not blow through your shock travel first, then increase the spring rate for the added weight from aerodynamic grip. Then potentially again depending on your overall setup.

I find it incredibly hard to believe a change in tires gave you 5 seconds, unless you went from a non racing slick to a racing slick.

There is no real data to back up the claim that over springing the front of the car will somehow give you better handling. If you try to google it you will find forum posts with anecdotal "My friend said this" or "That guy uses this in his setup and he is good". Can there be situations where the non driven end is highly sprung? Yes, but usually it is for a very specific reason, mainly for rear traction and not for turn in performance. The driver mod makes a lot of discussion around kinematics pointless. There are a million ways to skin a cat and each person drives different. You are doing, in my opinion, a massive disservice by making blanket statements. I will agree with, changes in total system stiffness will affect turn in. Such that if you are undersprung, yes you need more spring rate at whatever end of the car. Otherwise you are increasing the spring rate for what benefit, and for what compromise?

More spring rate = less mechanical grip. Period, end of. If you are adding front spring to the tune of 800-1000lbs you are way over sprung in the front and you are trying to add spring to cure issues arising from driving style (*note this != skill). Listening to "Kenny Brown" he says he focuses on the straight away speed and gives in to the cornering weakness of the s550. If so then sure it makes sense to run big springs up front to help give you traction, in a straight line only.

To have an understanding about total stiffness in the system, usually OE and race teams with lots of money will develop a goal for a particular ride rate. Then the rest of the suspension packaging is developed for the chassis / driver. In just about all cases where you hear wild and crazy spring rates is due to class, league, or some other restrictions in place. Such as some series with the gt 350 GT4 cars being limited to a soft, medium, or stiff spring package AND they cannot mix and match. So you have teams who run non optimal spring rates and they work with what they have because everyone else is in the same boat.

In general*
-Run as little spring as you can
-Run as little ARB as you can
-Dial in your low speed shock settings (if allowed) for your primary chassis balance

Just about every book, FSAE resource, and individual I have researched with does not agree with "More front spring ONLY, make car turn better"
A quick google search yields:

"Spring Selection
A spring change to a stiffer spring limits the amount of motion that the suspension undergoes in reaction to a particular acceleration (so does a change in CG height and track/wheelbase, but those are much harder to change than springs and for most practical purposes less effective too)

But there are upper limits on how stiff we can go with the springs, so we need a measure of "stiffness" to set the boundaries.

That number is the natural frequency of the suspension. Rule of thumb is rear NF slightly higher than front (by a tenth of a Hz or two - it keeps the sprung mass from pitching too much because the front wheels encounter bumps first so the rear needs to react a little faster) Street car: 0.8 Hz. Occasional autocrosser: 1-1.5 Hz. Full-bore autocrosser: 2.2-2.5 Hz."

RCVD-Milliken, Milliken
" Lateral Load Transfer-In a steady turn the lateral tire forces acting at the ground and the lateral inertia force (due to acceleration, Ay) produce a rolling moment which is reacted by changes in vertical wheel loads. The total rolling moment is distributed between the front and rear pairs of wheels. The distribution is performed in two parts. The first part involves the rolling ofthe body on the suspension springs about the roll axis of the suspensions. This part (the lateral inertia force times the vertical distance between the CO and the roll axis) is distributed to the front and rear tracks in proportion to the suspension roll stiffnesses. This is referred to as roll couple distribution. The second part (the lateral inertia force times the distance between the roll axis and the ground) is distributed in inverse proportion to the distance between the CO and the tracks and in direct proportion to the roll center heights at the tracks. Here again the details of the suspensions must be taken into account for accurate results. The roll centers may move laterally and vertically in a nonlinear fashion and affect the distribution of the load changes between the wheel pair. "
trackmstng.PNG
 
343
300
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
I know all of that theory. Lucky for me I have video prove.

First is without front swaybar and camber plates but 275/35 Square 140TW Semi-Slick tires brand new first day. Last season I was on OEM PZero 300TW tires.
Watch how the inside tire move in corners and how is lifting also in the first 2 corners you can see this happening to the right tire as well.


And after I added Camber Plates + Front Sway Bar end of season. Same 140 TW Semi-Slicks rears on over 200 laps fronts like 100 laps.
Notice how inside tire is not lifting as much and how the car is much more planted (adding grip to inner tire) in the first two corners transition. Also 3 seconds down in time just from Alignment + CC Plates + Front Bar + Driver Mod.


What I'm saying is that there is a reason why the GT4 cars run 800-1000 lbs front springs and that is not only because they have a ton of aero. There is also a reason why the GT350R rates almost 2xOEM PP spring rates are so loved across the S550 community. Also there is a reason why the AutoX guys run Coilovers and 450-500 lbs springs is not because the cars in AutoX have tons of aero.
 
Last edited:
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Lots of aero? On the front or the rear?

Specifically the front. If you had a meaningful amount of front aero and 500lbs springs that lowers the front rude frequency. And you would have less pitch.

Aero balance is very pitch sensitive and is a large consideration to both spring rate and damping rate selection (s).
 
Specifically the front. If you had a meaningful amount of front aero and 500lbs springs that lowers the front rude frequency. And you would have less pitch.

Aero balance is very pitch sensitive and is a large consideration to both spring rate and damping rate selection (s).

I have a Roush front lip which protrudes a little further that the oem lip and is supported by the front bumper, but it's no big downforce. But i'll confess..... I have a huge rear wing (pitch adjustable). Hey, I like the look, what can I say. I'll work on a more aggressive splitter next year, but even then, rules say it cannot protrude further than 2" ahead of the front bumper line.
 

TMO Supporting Vendors

Top