el es tu

Over the last year and a half of owning this car I have been playing with the suspension setup and would like some input from qualified people.

Current setup:
2007 C6 (Narrow body)
Pfadt poly control arm bushings
Pfadt camber plates

Front ZR1 33mm sway bar
Rear Z06 27.9mm sway bar along with 17.5mm base rear which can be swapped for varying grip levels

Front Z06 spring 531lb
Rear Base Spring 657lb

Front Z06 shocks
Rear Z06 shocks (the newer valving - not the older stiffer setup)

Zip corvette adjustable endlinks with custom hardware to allow for even more movement

Aligment specs:
I followed a more factory alignment style of more rear camber becasue Im running a setup whose balance is very close to what the factory tends to offer (f/r spring ratios and sway bar ratios). If I make the car understeer more, Ill feel comfortable using more front camber for better front end grip and turn in.

neg 1.4/1.5 front camber
neg 1.7/1.8 rear camber
toe 0.0 front and minimal (guessing it was -0.05; I cant remember exactly what it was but it was low) rear

ride height full stock height

endlinks adjusted to neutral without driver in car
driver weight approx 150lbs

*weight reductions are minimal (approx 5lbs off the front and 5 lbs off the rear)

Wheels and tires:
factory 2005- 2007 5 spokes
front tires BF goodrich g-Force Sport COMP-2
Rear tires Stock Goodyear runflats
Pressures (cold) 30 psi front 28 psi rear

The next tire set is going to be the Bridgestone RE-11 but Im not sure if I should wait to get wheels which can clear larger brakes (and z06 sized rubber - the re11 will be available in 325 in july/aug so it will be a wait but thats not a big deal) or just go with the stock sizing for now (and possibly go with spacers for brake clearance, which Im not sure may end up overkill - it seems like 1/2" spacers could push out too far) - brakes are totally stock except Hawk HP+ pads, high temp fluid, and z06 ducts. The bite is good, but the feel of the floating calipers moving when coming down from high speeds (150mph+) is not confidence inspiring so thats why Im adding this other complication to the fold. I do not intend on doing patchwork upgrades like ss lines or pistons since Ill end up losing out on them when they have to be replaced (looking into the AP T1 kit along with something to match the rear or Wilwood SL or WA - pad thickness is not an issue. cost is the biggest issue)


tire compound chosen:

http://www.tirerack.com/tires/tires....ke=Bridgestone


Use:
The car's use is primarily for rough surfaces - concrete patches, heavily crowned roads (backroads), some gravel, small jumps, and lots of quick tight transitions.

Im pretty happy with the reduced brake dive and stability of the car with the current setup, but im not sure if it would be wise to change up the sway spring and shock rates a bit further to smooth out corner exits and allow more power to be put down. Also going to stickier rubber may lead to a significant increase in body roll so thats why Id like some expeirences with these rates and the tires you run


anyway heres a list of potential setups (all are c6 parts unless noted. front parts first/rear parts second):

1. Current:
Springs
531/657

Shocks
Z06, Z06

Sways
Zr1/Z06 (or 17.5mm base rear)

2. Minimal modifications
Springs
531/657

Shocks
Z06/GS - GS would be used since they are valved closer to my rear spring rate

Sways
Zr1/Z51 (or C5Z06rear)
or T1 sways if they arent going to limit the suspension's compliance too much

This is the setup Id like to go with but like I said, Im not sure how happy the car will be when it gets the extra grip. Hence the T1 sway option added in.



3. T1 esque setup
Springs
582/657 (or z06 782)

Shocks
T1/GS (or z06 if that spring is chosen)

Sways
T1/T1

So what am I aiming for?
Lots of turn in, zero rear end jumpiness, enough stiffness to eliminate body roll in fast flat sections(this will be a concern with the softer tires), but enough compliance to conform to really crowned uneven roads (compliance is currently good), enough dampening to take jumps reliably (its actually pretty good now - 70mph over a foot high jump will land smoothly), ability to put power down at any point with the least amount of driver effort (always can be better), yet neutral corner exits (basically I want to get as close to having my cake and eating it too )

Ultimately Im thinking that Im going to have to run a more understeer package with juuust enough oversteer added in to to keep things happy. Input/experiences with these different parts, the spring ratios youre running, and with setting up your suspension for competition on rough surfaces is most appreciated!

JerryTX

Are you doing rallycross with a C6?

froggy47

I have never seen a set up with more neg camber in the rear than front?

Is this a c6 thing?

Anyway, not sure I qualify as a professional setup guy, I have done all these myself on c4 & c5.

Not to get to specific numbers,but,

lower it, stiffen it, more front neg (will result in accel wear inner edges - solution flip tires as needed), bigger bars, adjustable shocks.

FWIW

0Luke@tirerack

jumps ... really (I for 1 want to see the video)

150 mph on public streets (again VIDEO)

BFG front tires and Goodyear EMT rears (just a bad idea in general)

putting the power down at any moment is not possible as any car with decent power can break traction in many conditions regardles sof the tire selected

No mention of how you are going to fit a 325 tire under the narrow body rear fenders

I would suggest some light reading from my BLOG before spending anymore money

here's a link

geerookie

Since it seems like you are basically happy with how the car responds and reacts to your use now but want it to "feel" quicker and more responsive I would just getting rid of the poly bushings and getting spherical bearing replacements.
Then lower/set ride height for the front to 24mm and the rear to 70 - 78mm as measured from the LCA pivot point to the bottom of the lower ball joint. In other words the bottom of the ball joint should be that much lower than the center of the pivot point which is most in line with the ball joint. The rear range is based on how good your bump steer is controlled. High if not and lower if fixed.

el es tu

I wish! Large jumps and debris would mean a lot of of replacement bumpers
Right now Im working out getting another car like my dd (audi) for dirt.

With the C6 Im focusing on a hillclimb setup

yep the factory wants more rear camber than front. I believe BMWs do this too.
I dont like it, but Im trying it right now since Ive got the suspension balanced more like the factory would. It makes things more "stable" but at the cost of turn in.

Im guessing youre in the T1 Bars (or similar) camp? Do you ever have issues with them being too stiff?

Shocks - not sure on any cheap adjustables. Single seems reasonably cheap but the cost of doubles (from what Ive seen from Penske) is pretty high. The cheapest doubles ive seen are qa1 for about 1200 but the reviews dont all sound great. Not sure on viable alternatives.

Tires came with the car. I dont want to change them only to throw them out with new wheels hence the reason for running them until now.

325's: a few folks here have done this without tubbing. I think the key is the wheels and ride height. If you have any specs that say the contrary or if the tires will end up rubbing somewhere, please let me know so I can stay with the 245/285 setup - i definitely dont want to cut open a sidewall jsut for a few mm more rubber!

definitely not saying I did 150 the street - we cant talk about that here lest the mods come in and lock the thread! Not here to break the rules just get the car done

Jumps are not ramp jumps or anything major just really crowned roads with some unevenness which can send you in the air for a second or two when transitioning from one section to the next. Not Very common, and I typically dont aim for the center in these situations and get airborne but I want to cover my *** since the car will occasionally...

read the tire rack advice/blog several times a long while back its very informative

While I dont have experience in sanctioned events Im not 100% new (the minimal experience I do have consists of a few years of Karting several days a week when I was in college, driving/drifting cars offroad in mud/dirt, and unofficial races against friends/aquaintences who have raced in lower leagues and helped with some instruction). However I fully intend to get the car on some track days at vir with instructors just because I know there is obviously much more to learn especially with something as different as a large flat long course.


Ill definitely look into this

thanks for the input everyone; i appreciate it!

0Luke@tirerack

more negative rear camber causes understeer which is deemed dersirable by the factory for the average driver so, there are a few cars that run that type of set up.

froggy47

Factory dumbs the car down for those incapable of controlling a car that oversteers.

0Luke@tirerack

yes they do but, it's not GM or any other manufacturer it's the government forcing their hand ... gotta love federal regulations and the nanny state

froggy47

Well I mostly agree, air bags, seat belts, anti shatter glass, many more I am sure, but I don't recall, over my many decades of interest in all things automotive, seening any government rule/law that specifies that any vehicle must be designed to understeer in the hands of less than competent drivers when at the limits of grip.

Now I could have been out of the country (I worked overseas a few years in the 80's) when they passed this.

If I'm wrong & someone can link me to where the government understeer rule is please do, I want to study it.

What I think is the staff lawyers for the auto manufacturers prevail with the executives who then force the engineers to design it in.

Don't want granny drivin the the seedan to bingo & havin' to deal with an oversteer.

0Luke@tirerack

the DOT and NHTSA have been pushing benign handling and electronic safety aids since the Corvair. A simple google search will yield hundreds of documents dating all the way back to the late sixties detailing many if not all of the initiatives and FMVSS regulations and rulings. When looking for understeer requirements they are typically are tied to roll over rates. If you want to start somewhere take a look here

http://www.nhtsa.gov/cars/rules/ruli...nce/index.html

http://www.gpo.gov/fdsys/pkg/FR-2010.../2010-8159.htm

It's well known that they went directly after the 1995 BMW M3 and it's 17x7.5 wheels and 235/40-17 tires because of it's lack of understeer and neutral handling. It's argued that the 1996 M3 came with 17x7.5 front wheels with 225/45-17 tires along with 17x8.5 wheels with 245/40-17 tires to appease both the DOT and NHTSA and their understeer requirements.

all light passenger vehicles are required to have ESC systems starting 2012. That may have been one of the reasons there wasn't a 2011 Viper.

ABS, Airbags, TPMS and ESC are all designed to protect the population from their own lack of ability to control the car they are driving.

Most of the European manufacturers comply with these types of regualtions simply because the US market is so large but, they quietly endorse and prefer a graduated licensing program in addition if not over electronic driving aids.

We, the driving enthusiasts, are not alone as the entire motoring public will always be a target for protective legislation.

let's all quote Rodney Atkins in three part harmony
Thankfully, those manufacturers who produce performance cars have successfully lobbied that those invasive traction and stability control systems need to have a way to be disabled under certain situations. Just think of how much fun an AutoX or HPDE would be with the ESC/TCS systems were in full "you need to be saved from yourself" mode at all times.

el es tu

I dont see how plowing through a corner and not be able to change direction could be safer than still being able to turn... Of course there is the issue of over compensating steering input with an inexperienced driver - a la ford explorer rollover fiasco that lead people to believe it was the car or tires rather than the large numbers of soccer moms who owned the things...

TheSkunkWorks

Suggest you minimize the guesswork by first diagnosing precisely where handling characteristics are lacking during what cornering phases in which particular types of turns. My $.02

el es tu

Midcorner through corner exit - I want the rear end to be planted better so it can take more throttle input

I know my z06 rear shocks are for a stiffer spring setup, so Im set on changing out the rear shocks to the gs because theyll be better valved to my rear springs (softer than the z06 rear shocks) and let me put the power down sooner. For 110 bucks its a pretty cheap swap that should help that out.

If the car feels like it can go a little further, Ill bring the rear bar down to the smaller z51 rear bar sizing but Im doubtful that Ill even need it...

If I find too much body roll with the stickier tires, Ill eventually go to the T1 bars. But like I mentioned Im kind of hesitant to make the setup significantly stiffer and end up with a car thats skipping over bumpy surfaces.

thanks for the reply!

mountainbiker2

Just disconnect one end link in the rear and see what happens. I run no rear bar.

Steve A.

froggy47

Maybe I need to try it, Richard W. nicked me by a few tenths (scratch) last weekend with a missing rear bar on his GS.



So in (sort of medium) technical terms what happens with no rear bar vs rear bar. Looking for more than puts power down sooner, want to know why.

froggy47

Thanks for those links, but when I hit R-squared & linear regression I quit.



I think you are right that at least in an indirect way (rollover resistance) the gov't pinhead's are inclined to try (at least) to mandate how a company designs a car to handle.

Funny you mention the (top rated by R&T and C&D) 95 M3 as I have one and it is a sweet handling piece.

Witness the PIA that the TPMS systems are on C6's that are tracked.

Good call & thanks for setting me right.

meldog21

I learned the answer to your question when one of the arms on my Pfadt front sway bars broke (Pfadt bars are 3 piece, center torsion section with connecting bars on each end).

Keep in mind that this answer is independent of any other suspension changes, bar or no bar change only.

I didn't know the arm was broken, but in effect I had no front bar. It was only commuting, not at the track, but the results were the same. I noticed that on my regular freeway entrances/exits the rear end was loose. The normal acceleration and speed for the same corners I'm used to resulted in wheel spin. The front felt planted and precise, and the ride felt better (quieter and smoother) than usual. When I got home I jacked up the car and found the broken bar.

So, when you remove a bar from one end of the car that end will get more traction than the other end, relatively speaking. To address your question directly, when your buddy removed his rear bar it increased his rear grip.

There is a lot more involved in tuning the whole suspension of the car, but that is the simple answer that I think you were looking for (I hope that's what you were looking for).

Dog

froggy47

Thanks, always appreciate actual experience, but I wish for a little more, why does more grip happen? Is the front bar allowed to do it's work on the opposite end in a magnified way? Without counter resistance from the rear bar (that is now missing)?



I know there are a couple of classic texts on this, but I never seem to absorb it well enough to explain or remember it.

mountainbiker2

I had a very small Z51 rear bar. When I took it off, I had more rear traction. The front still hooked up the same. You have to try it, because the last time I hooked it back up, I had more rear traction. Confusing to say the least. I had different rear spring rate then before. So sometimes with different setups you get different results.

Steve A.