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Square tire setup and the sway bar dilemma

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I have 2013 Boss 302 (all stock except CC plate ) and I am planning to go square tire setup (293/35-18) for the track.
People have done square on the Boss and they noticed an increased oversteer tendency due to the fact that the stock suspension was setup for staggered tire sizes with 255 front and 285 rear.
So, naturally, I would think putting a smaller rear sway bar will help resume the neutral handling characteristics.
The question is, how small should I go?
My stock Boss rear sway bar is 25mm, GT is 24mm and the V6 is 22mm. Rehagen also carries 19 and 20mm too.

I understand there is no perfect answer, most people say use an adjustable rear SB or even both front and rear adjustable SBs, but I am resisting the bug strongly, hence I am aiming to replace the rear SB only and hopefully it will be a takeoff part from either GT (24mm) or V6 (22mm)...basically I want to keep it simple.

Note: I already had a few pm conversations with some bmo members but I decided to create a thread to have more inputs.

I appreciate your inputs
Rabee
Detroit
 
Addendum:
This to use a reference when discussing the subject. I noticed that the R/F spring rate ratio for GT is higher than R/F spring rate ratio for the Boss.

Quote:
.............................. Front Rear
Base GT.....34.6 mm 24mm 123 lbs. 156 lbs.

Brembo 34.6 mm 24mm 131 lbs. 167 lbs.

Boss 302 34.6 mm 25mm 148 lbs. 186 lbs.

Laguna Seca 34.6 m. 26m. 137 lbs. 191 lbs.
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
I was looking for the F/R spring rates for the P springs, could not find them but I remember that the fronts are stiffer then the rears. That does help balance out the car with a square set up since the softer (relative to front) spring rate in the rear helps traction. Thinking of leaving the rear bar as is and going for a stiffer front adjustable bar. If you do go for P springs, better get the LCA and bracket at the same time, really needs it.
 
I talked to Rehagen racing ( Bill) he thinks that 20mm rear sway bar ( 2005-2009 GT rear sb) will be ideal.
I asked a lot of people and most recommended adjustable front and rear bars.
Some said go as soft as 20-22mm...etc
I am leaning toward 20-22mm due to the fact that:

1) the turn in and mid corner balance will still be good ( theoretically) due to wider and stickier Rivals at the front. There is a huge difference between 255 p zero and 295 rivals. Obvious.

2) putting the power on corner exit effectively is expected when going 20mm rear sb due to better articulation of the rear tires and it is especially needed on a solid axle system like ours. Again 295 rivals will be stickier than 285 p zeros, which is a plus. I can soften the rear dampers to help in this department too.

3) One change only means less money to spend, if done correctly, of course.

Mad Hatter, Regarding going adjustable front bar, a lot of shops (including Filip-Cortex) said that the better investment will be going stiffer adjustable front bar and leave the stock rear alone.
 

JScheier

Too Hot for the Boss!
I think a lot of the differences in decisions to go with a front bar <or> a rear bar depend on other modifications (current or future) which will effect the results.

I think we can all say that the Boss is relatively soft in terms of spring rates.... and if you've tracked it, you've probably got photographic evidence of it.

With that being said, two schools of thought:

1. Soften the rear
2. Stiffen the front

For me, the decision (at the time) was to stiffen the front of the car. Why soften a car (that is obviously already soft) further? Stiffening the front worked great.

Now, in all honesty, I went with both front & rear adjustable bars (was too good of a deal to pass up)... but I knew all along that my stock springs were going to become basement toe-killers. As such, adjustable bars front and rear enabled me to try many different spring rates until I found one that I liked, and fine-tune that setup with the adjustable bars (and 2-way dampers). I have zero problem putting power down in turns (in, mid or out)... but that's lots of setup time on the track.

Either method is correct... and a 20mm (or no) rear bar is certainly a cost effective way to go.... just depends on your future plans and driving style. I ran no bar on my 1986 GT and my 95 Cobra... but I set the cars up spring rate wise to work that way.
 
I am working on a detailed review about the new square tire/wheel setup and the rear 20mm rear sway bar as well as Pagid RS-29 pads.

Stay tuned ...
 
Track: Gingerman raceway
The items changed:
1) 18X10.5 PF01 Enkeis with 295/35-18 Rivals all corner
2) Pagid RS29 from Pete
3) ATE 200 brake fluid
4) 20 mm rear sway bar (take off from 2005-2009 GT) got it from Rehagen racing for $70.

I started off with front dampers set to 5 ( always 5) and rear 1. It understeered mid corner and corner exit too.
Then cranked up the rear dampers to 3, it felt more neutral, but the magic happened when I set it to 5!!!
Extremely predictable and neutral with a mild safe push at some corner exits. However you can still, controllably, rotate it with the throttle.

The tires are extremely sticky, very predictable and give enough warning sounds before they lose the grip.
The sweet point pressure was 33-34 rear and 36-37.5 front.

The Pagid RS29s have great stopping power and I did not notice any fade for up to 30 min session.
Initially my brake pedal felt slightly mushy, but I realized the bleeding screws were sweating, so I tightened them and filled the brake reservoir and then everything became normal. The brakes finally gave me the confidence to brake deeper.

The only negative observation was that the car with the 20mm rear sway bar does not feel as "tight" as with the stock sway bar. You notice this with the initial turn in phase primarily.

Things I will change is to get -1.8 or even -2 camber instead of -1.5 due to outer edge tire wear.

Final note, I do not know how relevant this is, but going to 18 inch tires lowers the car and hence the center of gravity, it just felt lower to the ground when I sat in it :D
 
6,363
8,187
For me, the decision (at the time) was to stiffen the front of the car. Why soften a car (that is obviously already soft) further? Stiffening the front worked great.

FWIW if the car "pushes" creating a condition where the front end grips may not be the best way to go. In some cases causing the rear to unstick is a better method. Call it my short track stock car upbringing but if I have a car that "pushes" I will "loosen" the rear before I "tighten" the front. The reason is simple, if you continue to create grip in the end that moves you can end up with a car that just won't handle at all, it will be too tight all the way around. If you use the conventional method you can end up with a car that reaches it's loading capacity and suddenly loses grip instead of gradually meeting it's grip potential.

BTW try the blue Ford Performance front bar on the middle setting and an 18mm or no bar at the rear. You're on your own with the springs/shocks as we use Penske coil overs.
 

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