AST 4150 installed

[Jimmy Pribble]

How much camber are you running up front? I was going to try to set the spring rates so I could possibly drop the rear sway bar off. Then if it pushes, add a bigger front sway bar. Does that sound doable?

All of the Boss 302R race cars that I saw this weekend had rear swaybars about the thickness of a spaghetti. Just a data point. I like your plan better, but if the race teams are having to make a minimum weight anyway, no reason not to keep a rear sway assembly that has weight so low and to the rear. For track people not constrained by those kinds of rules, I would also attempt to just get rid of it altogether.

 

[DD GT3 RD]

I see people run no rear sway bar but why? Technically speaking

 

[Jimmy Pribble]

I see people run no rear sway bar but why? Technically speaking

In simple terms, more bar is less grip. That's why lots of FWD cars have rear swaybars as thick as my arm. They want less grip out back in order to rotate the car. The Mustang generally does not have a problem with this, so only needs as much swaybar as needed to manage the balance between the front and rear. If you can manage it with spring rates and other ways (tire sizes), then the rear swaybar can be removed and that is another way to shed a few pounds (even if it is in the wrong place).

 

[Zquez]

I see people run no rear sway bar but why? Technically speaking

Because if you run the right spring rates, its not needed. In a square setup which is prone to oversteer, you want a bigger front bar and smaller rear bar. In stock configurations or near stock such as regular lowering springs, the sway bar spring rate adds to the actual spring rate, allowing a car to handle like it has higher rates without sacrificing ride quality. Race cars run high spring rates, and the bar isn't a band aid to hide soft rates. Its there to fine tune the springs rates on the coilovers.

 

[ArizonaBOSS]

Just beware that if you dump the rear bar, you lose one "knob" with which to tune the handling of the car. And it's typically a lot easier to change a setting on a swaybar than it is to change springs on a coilover.

 

[Jimmy Pribble]

Just beware that if you dump the rear bar, you lose one "knob" with which to tune the handling of the car. And it's typically a lot easier to change a setting on a swaybar than it is to change springs on a coilover.

I agree and I'm sure that's another reason the race teams keep the rear bar, even if it is only spaghetti sized. However, I know very few non-racers who ever change anything on their setups, except for tires and pressures, no matter how many "knobs" they have. If somebody was honest with themselves and knew they were only setting-up the car to generally work well in most conditions (or for the two tracks that they ever go to ), then they could work to lose the rear sway and it's weight, without much worry.

 

[ArizonaBOSS]

Agreed, it's not a concern that everybody will have; just something to consider.

 

[DD GT3 RD]

Ahh I see. When I installed the coilovers I had the rear bar on soft and just raised it to medium. I felt a bit of understeer. I had dampers set 4 clicks from the top on the rear and 2 from the top on front. Maybe I should of just stiffened the rear dampening up more.

 

[ArizonaBOSS]

Well, if all other parameters stayed the same, moving your rear bar from "soft" to "medium" should have made the car more prone to oversteer (loose). Soft = more grip, stiff = less grip with respect to bars.

 

[Grant 302]

I see people run no rear sway bar but why? Technically speaking

Corner exit speed. It helps relatively high HP cars put down the power coming out of a turn. Cars that can lift the front inside tire transfer most of that weight to the inside rear.

 

[JScheier]

Just beware that if you dump the rear bar, you lose one "knob" with which to tune the handling of the car. And it's typically a lot easier to change a setting on a swaybar than it is to change springs on a coilover.

For those of us not arriving at the track in tandem 18 wheelers with 50 different spring sets and trained technicians, this is a very important point. If you only run at one or two tracks, then tuning a car to be good at those venues without a rear bar is probably pretty low effort and maintainable.

In my case, I run at 3 local tracks and several out of state tracks. Not wanting to carry multiple sets of springs with me, re-align and re-balance the car with each spring swap, having the adjustable bars gives me that extra 'knob' to help dial the car in. As an example, I always show up at Hastings unprepared (just how I roll). I can usually dial the car in within a couple of laps just by tightening or loosening the front or rear sway bars combined with the adjustable dampers. That's a 20 minute job vs. pulling struts to swap springs or dropping the rear axle down to swap springs.

Is it perfect? Nope. But until Drew or Jimmy become my pit crew... it's what I've got

 

[isrboss]

Very good point, adjustable sway are great for quickly tuning the balance. If I do give this an attempt, since the rear is the least complex to work on. I was going to just bring 3 sets of springs for the rear and drop the sway bar. Maybe bring a 24mm rear sway along. Just by following the Brembo set up, using slightly more rear rate (35lbs) than the front, is a good starting point. The only thing that I can see being a problem in removing the rear sway, the rates might need to be quite a bit stiffer in the rear. As we know to stiff in the rear can be bad on bumpy turns. So keeping the rear somewhere under 500lbs, would mean making the front somewhere under 450lbs. This could get in to an issue where brake dive is now not able to be controlled to ones liking. In the end it might just be better to keep a 150-200lbs softer rear spring then dial out the understeer with sways. You keep the straight line grip, and brake dive control.

 

[JScheier]

I went back and looked at my notes from my 1986 GT build up. In that instance, I had 425f and 250r with no rear swaybar and a 4cyl front bar. That car was equipped with an IPS watts link (Shawshank Redemption!).... with no room for a rear bar. It took me some time to get it dialed in.

The rear springs on this car were coil-over... so the rates are pretty darn close for a starting point. Fox bodies usually had the spring on the control arm, so the wheel rate was different than the S197 which have the rear springs on the axle. Since this car had rear coil-overs, the springs were darn close to the axle, so the wheel rates would be similar.

 

[Grant 302]

425/250 sounds a lot more doable.

So keeping the rear somewhere under 500lbs, would mean making the front somewhere under 450lbs.

I'd like to see what our cars would feel like with anything near 500# in the back! I wonder if that's the kind of setup on a drift car...

 

[DD GT3 RD]

425/250 sounds a lot more doable.


I'd like to see what our cars would feel like with anything near 500# in the back! I wonder if that's the kind of setup on a drift car...

its cause the mustang has the solid axle and needs to be softer in rear to put the power down I believe...check out KW M3 spring rates


M3 KW Clubsport
Front: 508 lb/in
Rear: 800 lb/in

 

[ArizonaBOSS]

I don't have ASTs, but if it helps to have another reference point I am running KWs w/ 515 front, 230 rear. Originally it had 400lb rear but was too difficult to get power down on exit, I switched to the 230 rears and played with the bars a bit and now I have the car set up like I want it +/- some minor rebound adjustments at various tracks.

 

[DD GT3 RD]

I don't have ASTs, but if it helps to have another reference point I am running KWs w/ 515 front, 230 rear. Originally it had 400lb rear but was too difficult to get power down on exit, I switched to the 230 rears and played with the bars a bit and now I have the car set up like I want it +/- some minor rebound adjustments at various tracks.

Very close to what ast supplies. I run 550/250

 

[zzyzx]

I see people run no rear sway bar but why? Technically speaking

The question isn't "why no swaybar", the real question is "why have a swaybar at all"?

As you can see from other answers to this question, the general consensus (which is correct), is that swaybars reduce grip (there are exceptions to this...). I can recall a seminar I attended many years ago where Carroll Smith bluntly stated: "swaybars reduce grip where you need it most". And he was for the most part, correct!

Which begs the question - why in the world do you want to reduce grip?

The short answer is ... you don't!

Swaybars should be seen as a tuning tool to address balance - the ratio of front end to rear end grip (understeer vs. oversteer) - used to remove grip from one end of the car, in order to attain a balance the driver is comfortable with.

Your first and primary goal in your setup should be singular: increase grip. After you've achieved all the grip you can given your setup, then and only then should you address balance.

I see so many people skip the "increase grip" phase and go directly to the "decrease grip" phase (via swaybars/damping/rake - balance tuning) that it's obvious they never had a chance to achieve maximum grip before addressing balance. This IMO is a very common mistake.

Also, the other consideration is the driver - each driver is "comfortable" with a different understeer/oversteer balance. A Miata driver who fully expects to swap ends if he lifts the throttle will tolerate a "looser" setup than somebody that drives FWD econo sedan. There's an old saying - "loose is fast" - which recognizes that front end grip is the limiting factor in how fast you can get through the corner. And on corner exit with all the power a Boss makes, you need to ensure that you can put that to the ground.

So, you need to maximize front end grip through the corner and maximize corner exit grip under WOT. A swaybar doesn't necessarily help with either of these goals, and that's a good thing to keep in mind.

 

[DD GT3 RD]

^great post. I agree but I'm not sure how to maximize front end grip anymore?! So I increase the rear bar to reduce understeer

 

[zzyzx]

^great post. I agree but I'm not sure how to maximize front end grip anymore?! So I increase the rear bar to reduce understeer

The answer to decreasing front "push" that many drivers don't like to hear is... be patient. 99% of the understeer is due to the driver pushing the car beyond its limits.

The point is - decreasing rear end grip - larger/stiffer rear swaybar - doesn't solve this problem. It only means that when it comes time to stomp on the go pedal, you have less traction available than you would otherwise on corner exit.

List of things I'd verify:

1. Front ride height. Did you lower your ride height in the front? If so, you probably decreased available front end grip. Stock the Boss is IMO already on the "wrong side" of having good front end geometry. There are solutions to this - like the extended LCA ball joints.

2. Alignment - camber. You have a good deal, but what you don't really know is if it's ideal for your setup. Only tire pyrometer readings and a meaningful interpretation of those readings will help. Consider the possibility that you may have too much neg. camber.

3. Rake. How does your current rake compare to stock? More or less? I've worked on many setups where 2/10ths of an inch difference in rake meant the difference between "neutal" balance and terminal understeer.

4. Tires/pressures/etc. Are you still running a staggered setup? If so, why? The only reason to run a staggered setup is if you're cramming the absolute largest tires you can under the fenders - because we know that you can stuff wider tire in the rear. Anything less than that and you should run a square setup.

5. Spring rates. Do you have enough spring up front, or not enough? I trust Terry in terms of getting this right, so I would assume you're "close enough". That said, given the weight of the 'stang and it's weight bias, the rate seems low to me.

6. Front swaybar. With your increased spring rates do you now have too much front bar? Either way, an adjustable front bar would be an ideal place to start. Put it on full soft and see where you end up.