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Discussion Starter #1
Anyone know the lateral acceleration(g's) of the stock suspension on our cars? Also any specs for the skid pad of a modified suspension?
 
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Discussion Starter #2
Ok I found some tests that state the stock lateral acceleration at .83 g's(Motor Trend) and .85 g's (Car and Driver). These sound low to me. I was also wondering if one could make these cars pull .95 g's. Lingenfelter got a 5200 pound Tahoe to do it, so I dont see why it would be so hard in our cars.
 
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Discussion Starter #3
Stock is around 0.82g.

If I had to make a well-educated guess, my SS now is a bit over 0.9g on the street tires, and around 1.0g on the autocross tires. Yes, the tires make a BIG difference
 
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Discussion Starter #5
Ed,

With Eibach springs, an f-body front bar, GW lowers in the rear, bilstein shocks, and 275/40/17 Victorracers or Goddyear F1's you think high .90's are possible. I know you said your car pulled 1.0 g, and Im sure you dont want to give up all your secrets to retain a competitive edge, but what all have you done you your car that is different.
 
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Discussion Starter #6
LOL, yup Ed's setup is Top Secret, "Eyes Only." ;)

Off the top of my head;
T56
F-Body front bar/slightly stiffer than stock rear bar(seriously)
GW front springs/stock rears
GW rear lower arms with DelAlums/aftermarket uppers(rubber bushings?)
GW DelAlum FCA bushings
HAL QA1 shocks
"Sport tuned" alignment
Torsen T2R

I need to get a GTech to see what I am pulling with the spindle spacers. I know it's noticeably better on the interchanges now...
 
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Discussion Starter #7
With the Victoracers and that setup, yes I think high 0.9x gs are possible/probable. Probably not with the Goodyears.

That is not saying the Goodyears are bad tires......in fact, they are very good for STREET tires. Better than my Yokohama AVS Sport street tires, as a matter of fact (which are pretty good in the dry, mediocre in the wet). Just there is a big difference in grip between even the "Best of the Best" street tires and a dedicated autocross/road race tire like the VictoRacer V700 or Hoosier R3S04/A3S04.

Only thing that Wayne missed on my setup (and it DOES make a big difference) is that I am running 275/40R17s on 17x9.5" in front and 315/35R17 on 17x11" in back. Even just going to 17x9.5" all around with the same exact tire as on a 17x8.5" rim (i.e. same 275/40R17 on either rim) will help a good bit.
 
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Discussion Starter #8
Does anyone know if Global West has ever considered making a full set of lowering springs? I know there front springs may lower .5", but have they ever mentioned a full set that would lower an SS 1-1.25". Also, if the front suspension camber gains were fixed to be optimal, could it be possible to see 1.xx g's on the skid pad?
 
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Discussion Starter #9
No they haven't, for a good reason. And this gets into why my car isn't lowered much either.

Namely, the suspension has a "sweet spot" geometry-wise where it works best. And, not surprisingly, it is pretty close to stock SS height.

BTW, the GW front springs basically don't lower an SS at all.

I don't think you'd see much cornering gain (maybe a little, but not lots) with the modified control arms versus a stock parts alignment that is "handling oriented". The real gain (IMHO) of the modified parts is that you'd be able to get the better handling WITHOUT having to run an alignment that is detrimental to tire life to do so (i.e. case on my car right now : handles great, but I'm not setting any tire life records
)
 
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Discussion Starter #10
Also, if the front suspension camber gains were fixed to be optimal, could it be possible to see 1.xx g's on the skid pad?
To put it in a different perspective, when Chevy High Performance did their article on the Pro-Motorsports Spindle spacers, they took an older Camaro(255f/275r/45-17s) from .87 to .90 and from 60.60 to 62.93 in the slalom. Not a huge difference, but pretty good for no other changes. They stayed with -3/4 static camber.

After installing them on my car and going from -1/4 to 0.0 static camber, the increase in responsiveness and precision were major, while giving MUCH better highway manners, and probably do much more to aid "real world" handling than a skidpad benchmark would indicate. I will try to get an Impala owner who is into AutoX to try my car out for his impressions, next time I make it to a meet.

Just ordered a G-tech, so I should be able to see how my car compares to the old magazine articles.
 
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Discussion Starter #11
The only thing the geotmetry would effect would be the roll center height. I dont see how lowering the car one inch would effect the angle of the upper control arm in relation to the lower conrol arm enough to effect teh roll center height if the alignment specs are kept the same.
If the roll center height did move, it would not be an inch, making the loss in center of gravity greater, and this would make roll angle less obtuse. This would equate to less body roll and better handling. Also, using the spindle spacer increases the angle relation between the upper and lower control arms making this angle more obtuse and shortening the convervence point closer to the center line of the vehicle. Doing this will raise the roll center height making the roll angle less obtuse. So, not only will the tire stay perpendicular to the road suface but now you have also lessened the cars tendency to roll. Doing some of the figuring has given me a better idea on the Sindle spacing issue, which I will be creating a new post about.
 
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Discussion Starter #12
You're forgetting one thing on geometry and lowering : the back half of the car ;) . IMHO, that is by far where the bigger "loss" (handling wise) from lowering is gonna happen.
 
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Discussion Starter #13
I disagree. By lowering the rear suspenison you will loose some of the lifting action that aids in traction, but you are also lowering the center of gravity where the reference for the lifting action is taken. Therefore the geometry would stay the same and or be better because of the greater effect the lower center of gravity will have over the slight geometry difference.
I am working on an idea for the rear sway bar that would allow the use of instant center brackets. This would fix any geometry issues and greatly aid the traction on the exit of turns.
 
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Discussion Starter #14
Throw a bit more power or gear at it (or a posi that actually does something), and get back to me. Stiffer springs (which all of the available lowering ones also stiffen things up) aren't the answer back there ;)
 
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Discussion Starter #15
According to Herb Adams you can fix body sway two ways, with a sway bar or with stiffer springs. Since I am runnng a stock sway bar with the GW lowers in the rear, the siffer springs will give the same effect as your similar setup with slightly stiffer rear bar(just not as much as an increase I am sure). I have 3.73's and an eaton with the 600lb springs. Right now is about perfect as far a being able to modulate the attitude of the rear end with throttle input. I am anxious to see what the 480hp 383 will do to this ability. The instant centers might be a must after the engine swap.
 
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Discussion Starter #16
According to Herb Adams you can fix body sway two ways, with a sway bar or with stiffer springs.
There is another way. Change the suspension geometry to raise the roll-center. The closer the roll center is to the center of gravity the less roll-torque is transmitted to the suspension. Line them up and the car would not roll at all, but then you'd have taken out the tuning of bars and springs. Of course, that's a moot point for our cars, I doubt you COULD move the roll center thant high...

Just a guess, but since I've installed the spindle spacers, I'd say the car rolls 1/3rd as much as before, with no other changes.
 
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Discussion Starter #17
According to Herb Adams in the rear you do not want the roll center to be high. It will make handleing inconsistent: i.e. handling characteristics will change as the suspension is compressed.
 
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Discussion Starter #18
OK, point I'm trying to get at is that even a pretty small increase in rear spring rate (via springs) results in quite a bit more difficult time in getting the car to hook up. It doesn't take much either....a 10-20% rate increase will do it. And guess how much the rear rate changes with about every aftermarket lowering spring for our cars ;)

My rear bar is the Hellwig bar BTW, which is 30mm solid and close to stock shape. The car could use a LITTLE more rear rate at higher speeds right now, but is very well balanced at lower speeds (i.e. autocross).

I am on the list for the instant center brackets as well.....should help the rear in a straight line, will be interesting to see what it does in the turns :D
 
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Discussion Starter #19
Originally posted by AutocroSSer:
I am on the list for the instant center brackets as well.....should help the rear in a straight line, will be interesting to see what it does in the turns :D
I think you and I (and other T56 guys) are both going to find that the instant centers that allow us to mount the LCA's "upside down" and thus put the swaybar above them to maintain ground clearance are going to find a LOT of benefit to handling with the ICB's as well...due to the fact that we should theoretically be able to push the car a good deal harder coming out of turns without the rear end rotating around. I am hoping that the effect on braking is minor enough that it won't have a significant effect on the speed at which the car can enter a turn. My car has a lot of static understeer right now, larger rear bar will help to fix that, but I think that will also bring the throttle induced oversteer out much worse (and it's already plainly obvious on my way out of a corner on the throttle if I am in the right gear entering the corner)...larger front bar will help that...but only to a certain point. This is where I feel that the ICB's out back will provide a significant gain...allowing me to run a lot of swaybar in the front to bring body roll down a lot and I am hoping it will also allow me to run stiffer springs in the rear. I want stiffer springs at a stock height so that the rearend doesn't sag down on me when there's stuff in the trunk, this means I might be pushing the car a bit too close to oversteer from the throttle when I'm holding the right gear and pushing the throttle to the limits through a corner...ICB's will help push the axle down into the pavement while I'm trying to accelerate out of a corner...and depending on my rear spring/swaybar choice, I think they will help provide just the balance I'm looking for in my car. Plus they should help me hook off the line quite a bit as well...something I couldn't do at all on my first visit to the track this year...hoping to go back and run some respectable times after I rebuild the T56 (that I finally took out of the car, so I have no excuse not to now).
 
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Discussion Starter #20
"In addition to front and/or rear stabilizer bars, changing spring rates can also be used to alter the understeer/oversteer characteristics. Highter springs rates at the front will increase the front roll stiffness vs. the rear roll stiffness....more front roll stiffness causes more of the lateral weight transfer to be absored by the outside front tire, which results in more understeer. Stiffer rear springs have the opposite effect, because they make the rear outside tire absorb more of the total lateral weight transfer." ch.16 Chassis Engineering, Herb Adams

This being said hear is the roll stiffness increase with our spring setups.
SS9C1Man-32.5% front, 28% rear
Autocrosser-69% front stock rear
and percentages with sway bar added
SS9C1Man-67.6% front, 28% rear
Autocrosser-104.1% front, 30% rear

With those specs I should have plenty of rear traction with the lowering springs. The Eibachs are progressive and the rates start out -7.65% less than stock and end at 48% stiffer(154 stock 143/228lbs-in. Eibach). I used a middle ground for the rear spec.

"In general, it is best to run as soft a spring rate as possible. The traction between a car's tires and the road is the only source for developing cornering power...Soft spring rates allow the tires to better follow the road...Higher spring rates can also limit suspension travel...Some car enthusiasts mistakenly believe that if 300lbs-in. coil springs are good, then 600lbs-in. springs have to be better. They're wrong...soft springs let the wheels follow road irregularities so that the tires can generate maximum adhesion."-ch.16 Chassis Engineering, Herb Adams
 
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