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Effects of a stiffer rear sway bar (other than mid-corner balance)?

37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
Hey All! I've been struggling to understand the theory behind this and wanted to see if TMO had any better insights to this.
What are the effects of a stiffer rear sway bar other than mid-corner balance? I've heard power-out is affected, but what about turn in?

Another thought I've had is this: let's say you have 2 setups: a soft front/rear and stiff front/rear bar setup.
Also assume shocks and springs are identical and both setups have the same roll couple distribution front-to-rear
Lastly assume the car is to be run on a smooth track (removes bumpy road compliance out of the equation).
In theory, would the cars handle identically? Or would there still be differences in turn in and power out from the stiffer front and rear?
(I presume mid corner balance should be the same since the roll couple distribution is the same)

I ask these questions because I have the FRPP track shocks (non-adjustable) and was debating on upgrading my PP1 rear sway bar to a PP2.
(PP1 is 22.3mm and PP2 is 24mm, roughly 66% stiffer)
I have BMR handling springs (250/980) and a BMR front sway bar (currently set to middle setting).
Mustang6g threads advised me to start with setup and recommended I not go any stiffer in the rear.
I'm hesitant to soften my front bar, as I feel like my suspension is getting very close to the bump stops while cornering
 
37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
What handling deficiencies are you trying to address?
Understeer on turn in and mid corner. Trail braking helps a lot, but I wanted to go further and experiment with the rear bar.

I'm a little concerned at if it would drastically change the car's balance during aggressive corners like T1 @ Sonoma or T6/T9 @ Laguna though - understeer is much better than oversteer in these cases
 
462
493
Exp. Type
W2W Racing
Exp. Level
20+ Years
Snowy North
Are you braking crazy hard prior to turn in...and/or holding the nose down via brakes on the way to the apex? Those BMR springs will challenge the rebound authority of the FRPP dampers, especially if you pound the nose onto the bump stops and then release the pedal quickly at turn-in.
 
37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
Are you braking crazy hard prior to turn in...and/or holding the nose down via brakes on the way to the apex? Those BMR springs will challenge the rebound authority of the FRPP dampers, especially if you pound the nose onto the bump stops and then release the pedal quickly at turn-in.
I generally ease off the brake before turning in. Usually only have around 25% of the brake engaged at turn in, and 5-10% of the brake engaged at apex before rolling back onto throttle
 
462
493
Exp. Type
W2W Racing
Exp. Level
20+ Years
Snowy North
Do you have an instructor friend who could drive it?

If not, then try tightening the front bar, run 10 laps under the watch and check times...compare vs original set--up. Could be that you are presently on the stops (which bump stops - have you trimmed them?)....and tightening the front bar will increase effective spring rate enough to get the load off of the outside front tire.
 

JDee

Ancient Racer
1,565
1,620
Exp. Type
W2W Racing
Exp. Level
20+ Years
halfway between Mosport and Shannonville
My thought is if you're using the non-adjustable Ford Racing shocks you should also be using the Ford Racing track sway bars and the Ford Racing track springs.
They were meant to work as a package, and they work very well together. It is an extremely well balanced setup for the track, and very liveable on the street as well.
 
56
88
Exp. Type
Time Attack
Exp. Level
10-20 Years
75024
A stiffer rear bar will affect all corner phases, but since you have understeer in 2 of the 3, it could work nicely for you. Maybe go to a bmr rear bar with some adjustment range there for fine tuning? I ran bmr bars and springs on my gt350. Square tire setup, about the same camber f/r. front bar was mid (on good year sc3) or full stiff (falken rt660), rear was mid. I tried the rear bar full stiff, seemed good, but on some hard corners I picked up inside wheelspin on exit, so backed it off and lap times stayed about the same.
 
65
64
Exp. Type
W2W Racing
Exp. Level
Under 3 Years
Scottsdale
Steeda released a new rear sway bar for the s550's. It is a softer bar than the PP1 bar on the 2 lowest settings and a little stiffer on the last setting. They said they are increasing the rear spring rates to 1100-1200 and lowering the sway bar rates to keep the rear tires on the ground thus improving their track times. I was told from them to run my street steeda rear bar on the softest setting (25%) stiffer than the PP1 bar but I am running the 900-1000 dual rate springs on the rear. I have a little understeer but mostly while coming out of the corners a little too hard on the accelerator. feels perfectly balanced going into and mid corner.
 
37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
Do you have an instructor friend who could drive it?

If not, then try tightening the front bar, run 10 laps under the watch and check times...compare vs original set--up. Could be that you are presently on the stops (which bump stops - have you trimmed them?)....and tightening the front bar will increase effective spring rate enough to get the load off of the outside front tire.
Yes they've been trimmed to BMR's specs. They're whatever came stock with the FRPP track shocks - I didn't buy any aftermarket ones

My thought is if you're using the non-adjustable Ford Racing shocks you should also be using the Ford Racing track sway bars and the Ford Racing track springs.
They were meant to work as a package, and they work very well together. It is an extremely well balanced setup for the track, and very liveable on the street as well.
Had I known about TMO before M6G, this would definitely be the route I would go haha. The car is *almost* there though! I'm thinking an PP2 or 350R bar (and nothing stiffer) would do it. I know the track bars come with a moderately stiffer rear bar and a VERY stiff front bar to compensate for this. I know it's not a true apples to apples comparison, since the FRPP springs are progressive and the BMR's are linear though

A stiffer rear bar will affect all corner phases, but since you have understeer in 2 of the 3, it could work nicely for you. Maybe go to a bmr rear bar with some adjustment range there for fine tuning? I ran bmr bars and springs on my gt350. Square tire setup, about the same camber f/r. front bar was mid (on good year sc3) or full stiff (falken rt660), rear was mid. I tried the rear bar full stiff, seemed good, but on some hard corners I picked up inside wheelspin on exit, so backed it off and lap times stayed about the same.
BMR bar may be the way to go if i find the PP2 bar not stiff enough, but I think it's not going to be a problem :)
In Randy Pobst's review of the PP2, he said he wished for a stiffer front sway bar to tweak the car to perfection

Steeda released a new rear sway bar for the s550's. It is a softer bar than the PP1 bar on the 2 lowest settings and a little stiffer on the last setting. They said they are increasing the rear spring rates to 1100-1200 and lowering the sway bar rates to keep the rear tires on the ground thus improving their track times. I was told from them to run my street steeda rear bar on the softest setting (25%) stiffer than the PP1 bar but I am running the 900-1000 dual rate springs on the rear. I have a little understeer but mostly while coming out of the corners a little too hard on the accelerator. feels perfectly balanced going into and mid corner.
From what I read, the specs were compared to the base GT bar, not the PP1 bar. M6G thread said it was going to be much softer than the PP1 bar, sadly. There doesn't seem to be any bar on the market right now where the softest setting is PP1 and the stiffest setting is PP2/350R, with a half-way bar setting in between. I would buy that in a heartbeat! Haha
 
37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
Are you squared on tires?
Yes, right now NT01 315/30r18 on an 18x11. I don't like them this wide on this rim, I'm getting lots of sidewall rollover at 34psi. Next track day I'll be upping it to 36psi. I'll be going back to 305/35r18's after this set haha.

I've been wondering if the size difference and sidewall rollover is causing the understeer - I'm going to Sonoma raceway this Sunday and trying 36PSI in the front to see if I get more grip. Front camber is -3.3 so I was a bit disappointed to see it roll over so much at 34psi.

Unfortunately I can't compare the 315's to the 305's since I also upped my camber from -2.6 to -3.3 when I switched over. With -2.6, the outsides of the 305s were obliterated to say the least! I presume the better tire fitment of the 305's (less bulge on an 11in wide rim) will help with sidewall rollover now that I have enough front camber though
 
NT01’s also have softer than average sidewalls apparently so this may be contributing, especially a 315 on 11j.

I’ve been trying to tune out some of the same characteristics in my car and still am working on setup but the few times I’ve gone in too hot and been forced to trail brake more the front is tighter. So thinking adjusting my driving style will likely be part of the solution.

I’ll be at Sonoma Sunday as well maybe we can link up and share our findings throughout the day.
 
37
32
Exp. Type
HPDE
Exp. Level
Under 3 Years
Bay Area
NT01’s also have softer than average sidewalls apparently so this may be contributing, especially a 315 on 11j.

I’ve been trying to tune out some of the same characteristics in my car and still am working on setup but the few times I’ve gone in too hot and been forced to trail brake more the front is tighter. So thinking adjusting my driving style will likely be part of the solution.

I’ll be at Sonoma Sunday as well maybe we can link up and share our findings throughout the day.

What group are you going in? I'll be with DriveTrackTime.com (TTm). Let's definitely chat!
 
204
154
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
A stiffer rear bar will affect all corner phases, but since you have understeer in 2 of the 3, it could work nicely for you. Maybe go to a bmr rear bar with some adjustment range there for fine tuning? I ran bmr bars and springs on my gt350. Square tire setup, about the same camber f/r. front bar was mid (on good year sc3) or full stiff (falken rt660), rear was mid. I tried the rear bar full stiff, seemed good, but on some hard corners I picked up inside wheelspin on exit, so backed it off and lap times stayed about the same.
Isn't stiffening the rear actually increasing understeer on turn-in mid corner if you don't change the front sway bar ?
 
204
154
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
From what I read, the specs were compared to the base GT bar, not the PP1 bar. M6G thread said it was going to be much softer than the PP1 bar, sadly. There doesn't seem to be any bar on the market right now where the softest setting is PP1 and the stiffest setting is PP2/350R, with a half-way bar setting in between. I would buy that in a heartbeat! Haha
To address your understeer on turn in just leave your PP1 rear bar alone and move your front BMR bar to the highest setting it still will not be stiff enough but will be closer than what you currently have.
 
206
210
To address your understeer on turn in just leave your PP1 rear bar alone and move your front BMR bar to the highest setting it still will not be stiff enough but will be closer than what you currently have.
Lots of variables but as a general rule I think it's the opposite. To reduce understeer, soften front bar or stiffen rear. To reduce oversteer, stiffer front and softer rear. It's a little counter-intuitive.

You also have to separate the feeling of sharp turn in response from understeer/oversteer. Lots of front roll stiffness, either through springs or bars, will make the car turn in very quickly and sharply, but then the car will settle into understeer.
 
56
88
Exp. Type
Time Attack
Exp. Level
10-20 Years
75024
Isn't stiffening the rear actually increasing understeer on turn-in mid corner if you don't change the front sway bar ?
For me it has been the opposite, the rear gets lighter, looser, but it affects all phases usually. Unlike a shock adjustment which could fine tune just 1-2 phases. Also car - to - car it can be different. With the same front bar setting my gt350 was slight understeer, and the gt500 is oversteer. Running a small 24mm rear bar on it now, with a bmr front full stiff.
 
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204
154
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
Lots of variables but as a general rule I think it's the opposite. To reduce understeer, soften front bar or stiffen rear. To reduce oversteer, stiffer front and softer rear. It's a little counter-intuitive.

You also have to separate the feeling of sharp turn in response from understeer/oversteer. Lots of front roll stiffness, either through springs or bars, will make the car turn in very quickly and sharply, but then the car will settle into understeer.
that's not how it works in a Mustang I can tell you that. I know the general theory but there are is a reason why Steeda released a softer rear bar for high spring rates. In the current case we are talking 250 lbs front springs with 980 lbs rear springs. Even with BMR swaybar on middle setting the front is just not stiff enough to get that sharp turn in. I'm on 500 lbs front with 800 lbs rear springs and with Steeda front bar on 2 hole with PP1 rear and the car is oversteering in long corners not understeering. I'm sure this will be a problem if I stiffen more the rear. Sure you will remove the understeer with stiffer rear bar but your car will be dangerous mid corner.
 
204
154
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
For me it has been the opposite, the rear gets lighter, looser, but it affects all phases usually. Unlike a shock adjustment which could fine tune just 1-2 phases. Also car - to - car it can be different. With the same front bar setting my gt350 was slight understeer, and the gt500 is oversteer. Running a small 24mm rear bar on it now, with a bmr front full stiff.
so we are on the same page bmr on full stiff with oem PP1 rear bar should help him. And the rear getting lighter on turn-in is not a good thing in fact is very unsettling if you are chasing fast lap times.
 

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