Rear sway bar

[svono50]

Eric, a larger rear bar will hold the rear down a bit and pull some of the force off the outside front tire a bit. This is why a larger rear bar will reduce understeer and move handing toward a more 'neutral' disposition. Anything larger than our rear bar is an improvement for the better.

[Bruce]

If you go bigger in back then what in front? Ted I know you have a larger front too is this a must have at that point? I have a 94 GT rear bar in the garage but the front SVO bar is bigger than the front GT bar!

[svono50]

It is all about the ratios of the front to rear sway bar diameters and their effective spring rate. You don't have to increase the front bar because you up the rear, unless you get the point where you start lifting the inside rear, like a lot of FWD vehicles do. The combination of springs also compounds things and changes balance as well. Using a bar stiffness calculator that I found out on the interwebs, here is what kind ARB (Anti-Roll Bar) spring rates change with size for the ones I have calculated both front and rear:

Stock SVO (F) = 30mm = 2315 lb/in
Eibach-Fox (F) = 35mm = 3694 lb/in [+60%]

Stock SVO (R) = 17.3mm = 65 lb/in
Stock GT (R) = 21mm = 142 lb/in [+119%]
Eibach-Fox (R) = 25mm = 285 lb/in [+339%]

I am currently running both Eibach front/rear bars on my car and combined with the Pro-kit springs it flattened things out a lot, but a drawback was that my inside rear had a lot of spin if I tried to power out of a corner on both the road and auto-x courses. The Eibach bars are 35/25mm (F/R) with the front bar being hollow, so its equivalent solid diameter calculates out to be 33.5mm. I went back to my GT rear bar (21mm) to see if it would help and it did lessen the rear inside spinning without adding much 'push' to the car...but I wasn't satisfied I had found a happy balance.

I then installed the MM HD adjustable rear lower arms and Wolfe Race Craft upper axle spherical bushings to make all (8) points solid spherical in concert with my Watts. I did some suspension motion testing without the springs installed and found a HUGE bind in the rear suspension as the roll centers of the stock 4-link and Watts were not playing nicely and also contributing to a huge rise in the rear roll stiffness...hmm, can you say lifting the inside rear...I knew you could. I decided to try the PM3L (Poor Man's 3-Link) by removing the passenger upper arm and voila, the rear roll bind was flat out gone and allowed a nice smooth axle rotation around Watts defined roll center. I put everything back together with the springs and decided to put the Eibach rear bar back in. Results were that I now had plenty of rear grip to power out of the corners earlier than ever before, but now I am almost lifting my inside front...doh! You could tell the rear of the car was now rolling over a lot more compared to the front.

I now have a couple choices to correct the imbalance (i.e.- too soft rear roll), 1) raise the Watts roll center or 2) get stiffer rear springs. Raising the rear roll center brings is closer to the center of gravity of the car height, which reduces the leverage the car has to roll over the rear. Obviously the easiest change is adjusting the Watts prop shaft higher in the frame, but I don't think that is the 'best' solution. I am planning on chatting with Maximum Motorsports this spring to see if I just need to get a pair of their higher rear springs on order and if so, which version as they have (2) unique rates. I would hope they would have a good suggestion which ones would match my Pro-kit fronts.

Whew, that is enough info for now.

[SVOeric]

so you're running with JUST a 1 upper control arm, interesting. I guess the watts link locates the rear, so it's not really a big deal.

[Bruce]

I have considered the poor mans 3 link. Do you run the quad shocks? My thought was without them I would need the 2 uppers to keep the rear end from wheel hop. Mine didn't seem to bind when I jacked it up and down without springs but its hard to tell with the jack doing the heavy lifting and gravity doing the rebound. Never came off the jack at any rate. Have had no problems with wheel lift in corners though.

[svono50]

Eric, yep, just one arm up there to prevent axle rotation. The Watts now handles all side-to-side control action as well as the wheel articulation about the Watts propeller shaft. I now need to figure out where I can mount my GoPro up in there to get some video of all the action going on.

Bruce, I removed my quad shocks when I went to the PM3L. At that same time I went to spherical bearings at the remaining (6) control arm points, so there is no more axle wind-up to worry about from compliant bushings. When I bolted everything together w/o the springs, I set the axle to the static ride height with the lower shock mounts sitting on the tops of the jack stands. I then lifted, by hand, one end of the axle to get it to pivot, the force required to pivot the axle rose very, very quickly until it literally 'cammed over' and the end of the axle popped up out of my hands and just stayed cocked up in the air. After a few minutes of looking at everything and scratching my head, I pushed down on the axle end and it did the same 'pop' downward to sit back on the jack stand. I tried it a couple of times and noticed my Watts axle clamps were flexing and determined there was something not geometrically meshing. I unbolted one Watts link from the axle mount and moved the axle again, this time no camming over/bind/pop, just smooth movement. I positioned the axle end where the greatest force was originally felt and held the loose link up to its mount...it was a full 3/4" offset from the mount...YIKES!! I then brought everything back down, bolted up the Watts link and pulled the passenger upper arm off...voila, no bind and smooth movement throughout the 'normal' range of motion (i.e.- up, down and rotation). When I took it out for a test drive you could tell the rear suspension had more movement/compliance now that the binding was removed.

As I stated, the exit traction out of the turns was much improved, but you could tell the outside rear corner of the car was now dipping and it felt like the car moved from pretty neutral to a slight understeer. This shift in feel is to be expected, since when you either increase the front roll stiffness or decrease the rear roll stiffness it will shift toward understeering, especially now that the rear tires have more traction and can effectively 'push' the fronts coming onto the power. Increasing the rear roll stiffness will help bring me back to a more 'neutral' feel.

Now if I would have a nice 'tight' Trac-lok or a Torsen differential, I likely would have never noticed the issue of spinning the inside rear. Kind of glad I had not yet decided to do something with my differential, as it would have masked this suspension issue. This worm hole of a suspension modification is certainly a deep one, but interesting none the less.

[strangesvo]

A lot of good information to take in here. Just to caveat on what svoEric mentioned earlier about the rear lifting more than you like. Like others on the site I to have experienced the inside wheel spinning during corner exit/acceleration. So without going out and spending thousands $ I figured I would begin here. First was chassis stiffening and tires, then springs. Now my next step is LCAs adjustable to level the car and larger sway bar. I don't think this will completely solve the problem but I think it will help tremendously. I am not a suspension expert by any means so I take what I read and my personal preferences and see how it works. I'm trying to be slightly more competitive with these new cars. Fact is I enjoy improving my car's set up just as much as driving it. Lots of great information on this forum, really appreciate the help. I plan on updating this after the next event just to complete the thread. One last thing. Of all the badass cars at the local autocross event I get more people checking out my car then any other. I'm sure you guys get the same thing.

[SVOeric]

While I think installing sub-frame connectors was the BEST thing I've ever done to increase handling of the car, in some ways it hurt.

while it may have made the car feel more 'together' it also made the rear right raise higher when the left front was dipped into a turn. while that flex in the body isn't a good thing, it really IS a good thing to keep the tires on the ground.

[gbeaird]

SFCs on a unibody car is ALWAYS a good thing!! I have the cracks in the roof to prove it. Tune the chassis around it.

But that's just me.

[SVOeric]

oh I agree with you Gene, a flexing body is never good, until it flexes enough to keep the wheels on the ground

[svono50]

Strangesvo, There are positives and negatives to every modification, rarely do you get a double positive...at least from my experience so far. I did all the 'basic' things first, then recently decided to dive in both feet at the deep end of the suspension pool, but I know I am really only in the 'medium' depth section compared to a lot of folks out there. You certainly don't need to spend $$$ on your suspension to improve it quite a bit, but the costs do run up exponentially as you try and reach a much higher peak. I do also know about the interest factor at local auto-x events, I get it every time I get a chance to get to one. Folks usually say, "Hey, I remember when these first came out!" or "I haven't seen one of these in years!" Most everyone compliments me for taking it out and having fun with it rather than letting it collect dust in the garage.

As far as sub-frame connectors, they are one of the first things anyone should do! It is amazing how much more solid the car 'feels', which has a lot to do with supporting the rear seat mounting points and firming up the seat. My car felt like a new car after I put mine on.

[Bruce]

I have heard this so many times. When I put mine in I didn't notice any difference when parked. I have had people get in my car and say you have subframe connectors don't you. All I could think was how flexible are their cars?

[svono50]

I have heard this so many times. When I put mine in I didn't notice any difference when parked. I have had people get in my car and say you have subframe connectors don't you. All I could think was how flexible are their cars?

I guess it matters on the technique of getting into the seat. If you 'roll' onto the seat cushion as compared to 'dropping' onto it, you may not notice it as much. My former 80 Mustang had a cracked floor pan under the outboard rear seat mount back in the day. We welded up the cracks and it made the seat go from a Lazy-boy to a racing seat as far as stiffness. The change in my SVO was much less dramatic, but still noticeable with the subframes.

[strangesvo]

I said I would give an update after the next event I participated in. Just to recap. In the rear I have Eibach sport line (progressive rate) springs, shock rebound adjusted to full firm, MM adjustable lower control arms, stock rubber upper CAs, 21mm rear sway bar, BF g-force comp2 tires. Front also has the sport line springs, strut rebound to full soft, have about 2degrees neg chamber.
So with the new control arms and larger sway bar and full firm shocks in the rear i eliminated the understeer but induced some oversteer. I was very happy with how the car handled, I felt like I could push the limits of the car more. I wish I would have played with the tire pressure a little. I just didn't think of it at the time. After the event I was chatting with another racer, mentioned he reduced Tire pressure by 3 lbs and gained 2 seconds on his time. So I think for next event I will firm up the struts to see how it acts. From here on I think I will improve one thing at a time to see progress. Another mustang racer mentioned a larger front sway bar to settle the rear, I will keep that in mind but first I will mess with the struts. I was doing some reading about car handling and it mentioned that one of the most important things is to match your springs to your shocks/struts. One will counter act the other if not matched properly, so that's what I'm going to try to achieve.

[SVOeric]

lowering tire pressure can help, usually helps get a bit more grab, at the expense of a slight bit more 'sway'

if your tires are biting, lowering the pressure won't help. There's also the old --shoe-polish test
put the shoe-polish over the edge of the tire and onto the tread. You can then see how much the tire is rolling, and you can tell if it needs more or less pressure