Rear swaybar?

[Jim Ryder]

The last few track days I've done since taking a bunch weight out of the car, I've had a issue with the inside rear wheel spinning off the tighter corners. I have a 36mm front bar and a 26mm rear bar. The big rear bar really helped the car when it was at full streetcar weight. I'm thinking that the car being lighter I need a smaller rear bar?? 18mm? For
the most part the car is handling really well and is the fastest it has ever been at Blackhawk Farms 1:17:56! I don't think there is a problem with the diff (torsen). I'm running the rear shocks pretty soft as well. I even put the battery in the right rear corner! This is the biggest issue I have to solve this winter. Going to do alot of little tweeks here and there to try to get a little faster again!! what do you guys think??

 

[BKBoss302]

Following this. I am contemplating removing the rear sway bar altogether. Any opinions are welcomed. I am currently running a BMR-SB042 25mm adjustable bar set to the softest setting of 224 lbs/in.
Looking at the info below I probably have too much sway bar.
REAR S197 Bars:
Ford 13mm Solid (Boss 302S):............ 18 lbs/in
Ford 18mm Solid (Convertible):........... 55 lbs/in
Ford 20mm Solid (2005-2010 GT):....... 96 lbs/in
Ford 22mm Solid (2011+ V-6):........... 147 lbs/in
Ford 23mm Solid
Ford 24mm Solid (2011+ 5.0, GT500): 193 lbs/in
Ford 25mm Solid (Boss 302):............. 250 lbs/in
Ford 26mm Solid (Laguna Seca):........ 275 lbs/in
Ford 22mm 'Blue' bar M-5490-AR (Part of M-5490-A kit)

Eibach 25mm: 130, 145, 175 lbs/in
Strano Performance Parts 8419 1" tubular: 162, 185, 225 lbs/in
BMR-SB023: 146 lbs/in
BMR-SB042 25mm: 224, 259, 302, 356 lbs/in
Whiteline 27mm 'calculated' from stated increase over 24mm?GT bar: 266, 309, 357, 411 lbs/in

 

[blacksheep-1]

the general rule of thumb for these cars is the ford Performance "blue" bar up front and the 18mm or no bar in the rear. don't ask me for part numbers, they are around here someplace, but pretty much everyone is aware of them by their slang name.
You might want to watch the videos of the T1 and T2 cars at the runoffs for some ideas as well,

 

[Jim Ryder]

Following this. I am contemplating removing the rear sway bar altogether. Any opinions are welcomed. I am currently running a BMR-SB042 25mm adjustable bar set to the softest setting of 224 lbs/in.
Looking at the info below I probably have too much sway bar.
REAR S197 Bars:
Ford 13mm Solid (Boss 302S):............ 18 lbs/in
Ford 18mm Solid (Convertible):........... 55 lbs/in
Ford 20mm Solid (2005-2010 GT):....... 96 lbs/in
Ford 22mm Solid (2011+ V-6):........... 147 lbs/in
Ford 23mm Solid
Ford 24mm Solid (2011+ 5.0, GT500): 193 lbs/in
Ford 25mm Solid (Boss 302):............. 250 lbs/in
Ford 26mm Solid (Laguna Seca):........ 275 lbs/in
Ford 22mm 'Blue' bar M-5490-AR (Part of M-5490-A kit)

Eibach 25mm: 130, 145, 175 lbs/in
Strano Performance Parts 8419 1" tubular: 162, 185, 225 lbs/in
BMR-SB023: 146 lbs/in
BMR-SB042 25mm: 224, 259, 302, 356 lbs/in
Whiteline 27mm 'calculated' from stated increase over 24mm?GT bar: 266, 309, 357, 411 lbs/in

View attachment 69307

My street Beast!

 

[Dave_W]

My street Beast!

What wheels are those? Love the Minilite style.

Regarding the rear bar, I'd start by using the info from https://trackmustangsonline.com/threads/s197-spring-and-sway-bar-rates.13152/ to compare your current bars & settings to the stock bars - divide the current rate by the stock rate to get a percentage for each end. I'm thinking you may have gone to a relatively stiffer rear rate from stock. To keep the Torsen from spinning the inside tire, you need to get some more load on it (or transfer less away) so you need to either stiffen the front or soften the rear. If you soften the front, you may need to dial in a bit more static negative camber to counteract the increased front roll and keep the contact patch flat.

Bigger picture, you say you've removed a lot of weight, but from where - do you know corner weights before & after? Even an estimate of front vs. rear and height of the item removed/lightened can give you an idea of the difference in roll force/weight being developed by the body/chassis (sprung weight) at a given lateral g load. For example (if I'm doing the back-of-napkin evaluation in my head correctly), moving the mass of the battery from the front to the rear means you've reduced the lateral force/weight being resisted by the front roll bar and increased the force/weight being resisted by the rear bar in a turn. So without changing the actual roll bars, you've changed the ratio of front-to-rear roll bias in a way that would increase the wieght transfer off the inside rear tire. I think. @Norm Peterson or @ShatterPoints may want to check my math.

 

[blacksheep-1]

Let's just make it easy on him...
although it doesn't really get into the suspension, the rest of this info is pretty good

http://files.world-challenge.com/vehicletech/vts/2016-PWC-VTS-GTS-Ford-Mustang-Boss-302-GT-2012-2012-v24.pdf

 

[Jim Ryder]

What wheels are those? Love the Minilite style.

Regarding the rear bar, I'd start by using the info from https://trackmustangsonline.com/threads/s197-spring-and-sway-bar-rates.13152/ to compare your current bars & settings to the stock bars - divide the current rate by the stock rate to get a percentage for each end. I'm thinking you may have gone to a relatively stiffer rear rate from stock. To keep the Torsen from spinning the inside tire, you need to get some more load on it (or transfer less away) so you need to either stiffen the front or soften the rear. If you soften the front, you may need to dial in a bit more static negative camber to counteract the increased front roll and keep the contact patch flat.

Bigger picture, you say you've removed a lot of weight, but from where - do you know corner weights before & after? Even an estimate of front vs. rear and height of the item removed/lightened can give you an idea of the difference in roll force/weight being developed by the body/chassis (sprung weight) at a given lateral g load. For example (if I'm doing the back-of-napkin evaluation in my head correctly), moving the mass of the battery from the front to the rear means you've reduced the lateral force/weight being resisted by the front roll bar and increased the force/weight being resisted by the rear bar in a turn. So without changing the actual roll bars, you've changed the ratio of front-to-rear roll bias in a way that would increase the wieght transfer off the inside rear tire. I think. @Norm Peterson or @ShatterPoints may want to check my math.

The wheels on my street Boss are from a Saleen Parnellli Jones special! Ya I love the vintage Trans Am look!

 

[stevbd]

As one reference point, and as @blacksheep-1 mentioned, in my 2011 GT I just removed the stock 24 mm rear bar entirely and personally I love it. I still have the stock front bar. The rear is noticeably more stable on corner exit and you can get on power much sooner. Rides better on the street too, it's more supple over bad pavement.

At some point I need to get the front blue bar or similar, mostly for adjustability, and I will try the 18 mm rear. I do have some slight push mid-corner but it is mild and may even make me faster because the car is so stable.

I have 400/200 Cortex coilovers and run 305 square on track with 25 mm front spacers. Theoretically the extra track width created by the front spacers may be reducing the understeer you'd otherwise get with no rear bar?? Not totally sure about that, I haven't run without the spacers on track.

 

[Jim Ryder]

As one reference point, and as @blacksheep-1 mentioned, in my 2011 GT I just removed the stock 24 mm rear bar entirely and personally I love it. I still have the stock front bar. The rear is noticeably more stable on corner exit and you can get on power much sooner. Rides better on the street too, it's more supple over bad pavement.

At some point I need to get the front blue bar or similar, mostly for adjustability, and I will try the 18 mm rear. I do have some slight push mid-corner but it is mild and may even make me faster because the car is so stable.

I have 400/200 Cortex coilovers and run 305 square on track with 25 mm front spacers. Theoretically the extra track width created by the front spacers may be reducing the understeer you'd otherwise get with no rear bar?? Not totally sure about that, I haven't run without the spacers on track.

I'm running 275's square, I hope to buy wider wheels and go to the 305's at Blackhawk Farms but stay with the 275's for Road America as it is not as tight. I think I may try the stock rear bar as it is much lighter than the 26mm on there now. also will try it unhooked as well. I don't want waste money on parts I don't need. It seems from what I've read the 18mm is what most like so that may be a good choice. The car is really good overall, trying to squeeze a little more out of it.

 

[Albino500]

FWIW - I've seen Kohr use the Steeda 36mm front bar and a factory 22mm rear bar on some of their late S197 cars. I've used the KR 34mm front bar with a 18mm on the earlier S197 cars that I've built. If you need a 18mm factory rear bar - I do have one out back I'll sell. JS