SnipeUout

Just got a 2012 Coupe and the suspension is well.... Not good for autocross.

I want to stay in the stock class. If I go with Z51 bars and Z06 Shocks will I stay Stock? If not what's my best course of action?
I also have a new Set of Eagle F1 GS-2 EMT... so that's my biggest limiting factor.

69autoXr

Shocks are free in Street and Street-R.

You can change either the front or rear sway bar, but not both.

Alternatively, you could install factory available option packages, but you have to install the complete package. That is, if you wanted to put Z51 bars front and rear, you would have to install the complete Z51 package, including springs/coolers/brakes/body features etc., you can't pick and choose between components. However, this is subject to availability of the package for the model year, and I don't think the Z51 was an option available for the 2012 MY, so I don't think you could do that legally.

All that said, for 2014 the C6 is in A-Street (AS), or Super Street R (SSR), depending on tires.

08velocity

I'm guessing you have autocrossed before !!! but if not, the best mod is to as I and I'm sure alot here have been told is " tighten the nut behind the wheel " corvettes are great handling cars off the get go, if you've never done it, go see how you and your car does then if you need to mod a bit go for it !!!!! just my 2 penny's.

B Stead

The ride height is adjustable by spring pre-load but with pre-load the suspension gets stiffer when raised and softer when lowered. So try different ride heights
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SnipeUout

The 2012 coupe suspension is way way to soft. I hope z06 shocks will help alot. I'd really hate for one basic mod to put me out of A-stock but I want my car to be competitive in A-stock. The courses here are very technical and I need the suspension to be predictable. Right now the car seems to float which isn't good.

Solofast

Ride height does not effect stiffness. The lowering bolts simply change the height of the vehicle relative to the springs. That is, the springs are deflected exactly the same amount, but the suspension is moved relative to the springs. Only if you slam the car down on the bump stops will ride height effect the stiffness of the suspension.

"Floatiness" if there is such a word, is often the result of insufficient rebound stiffness, stiffer shocks will help that a lot.

If your car is legal with the complete Z51 package, you will be a lot better off installing the entire package of springs and sway bars (shocks are free so they don't count). As a practical matter and while you are getting it all together, I'd just put on the bars to start with and look for the right springs and run the car in stock. It's not like you are gaining an advantage with the soft springs, and if you are just running local events nobody is going to protest you for running too soft a set of springs.

Once you get the right springs, get them installed, corner weight the car and align it and enjoy.

Autocross is supposed to be about learning, and getting out there and having fun. Only when you start beating a lot of folks do you need to make sure that your car is per the rulebook legal, since they deserve to get beaten by a legal car. If you're a newbie just starting the sport and learning, put on the bars, start looking for the right springs and have some fun.

JiminVirginia

If I were you, I'd just call Sam Strano, who is a set-up ace in addition to being a great driver. He would probably save you money, if anything. I'm guessing he'd recommend a front sway bar and Konis, with better tires (and he can probably suggest some to try, with details about vendors and alternative wheel diameters, if you want to entertain that). http://www.stranoparts.com/searchbym...=30&ModelID=12

ltborg

Here's another vote for Sam. He set me up with the Konis I ran the past two seasons as well as the bars I still use on my car. The only reason I'm selling the Konis is because I wanted to try my hand at tuning doubles and messing with canister pressure.

Solofast is spot on with his advice. Work to find the Z51 setup and install as you find it.

Ramo7769

The idea of stock class is running mostly stock compliance rates. You can't really stiffen the car and keep it "stock." Just one sway bar is allowed so you can adjust balance. You can improve the transient behavior by upgrading dampers. With this you can "hold the cake together" and compensate for springs that are too soft. That's the main idea behind stock class (Street now). Can't change the guts of the chassis. Can only tune what you've got.

If you're running street tires (A-Street), you can't really run square (widths) like the SS guys, so a front bar isn't necessarily the way to go. My advice is to drive the car. If you're frustrated with the balance at steady state, upgrade the sway bar on the end of the car that has too much grip.

If the car is too soft and you want to change that with springs and sway bars, go to the next class. Easy for me to say... I have a C5 and I'm going to STU...

Solofast

You're missing the point. He as the base suspension. He can upgrade and stay in class if he goes to the Z51 springs and sway bars. He isn't trying to change the balance and doesn't want to use the bar allowance to try to stiffen the car overall (your first paragraph is correct, the bar allowance is specifically made to preclude that). But the OP just wants to get the firmer suspension, that he's allowed to have if he had the Z51 package and run in the street class.

Since the Z51 bars (both front and rear) are legal when used with the Z51 springs, he asked the question if he could just upgrade the bars, and the answer is technically no, to be legal he needs to put on the springs too, but as a practical matter nobody is going to complain that he doesn't have the right springs since he's going to be slower with the soft springs on the car anyway.

B Stead

Changes in spring pre-load do not change the spring rate and that because the spring is not physically changed. But changes in spring pre-load do change the force range of the spring that is being used.

For example, a 200 lb/in spring requires 200 pounds to compress 1". But if the spring is pre-loaded 1/4" then 1" of suspension compression requires compressing the spring from the 1/4" point to the 1.25" point and the 1.25" point represents 250 pounds of force.

And there are sources on the internet that show the graph of increased spring pre-load as a mathematical translation of increased spring force. The spring rate hasn't increased but the spring force (as the spring is being used) has increased. Spring pre-load "translates" the use of the spring to a different force range of the spring.


Well, the first graph is a stock spring:

http://www.sportrider.com/tech/146_9.../photo_01.html

Then the second graph is a stock spring compared to a spring with a higher spring rate:

http://www.sportrider.com/tech/146_9.../photo_02.html

And the third graph is the stock spring compared to the stock spring with pre-load:

http://www.sportrider.com/tech/146_9.../photo_03.html

The negative spring travel that they show in the third graph is a little strange but that's where they show the amount of spring pre-load at 35mm
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Solofast

Nonsense,

It doesn't work that way since there is no preload when the car is sitting on it's tires, the spring position and forces are the same in this case, lowered or not lowered...

Think about it for a moment, the load on each wheel has to be the same, since the car weight hasn't changed. Therefore, the force on each end of the spring is the same no matter what position the lowering bolts are set at. Therefore, the amount of compression in the spring is the same and the rate has to be the same.

The only difference is how high the car sits relative to the ground, and this is simply a function of how much space there is between spring and the suspension. The spring rates are the same, the spring forces are the same when it is sitting on its wheels. Changing the bolt position so as to lower the car actually reduces the preload on the spring in the fully extended position, but that is meaningless once the car is sitting on its wheels.

The "preload" is meaningless because the spring isn't on the extension stops after it is sitting on the ground. What you are saying about preload only has meaning if the spring is on an extension stop and that isn't the case here.

Think of it this way. If you stood on a spring and the spring had a rate of 100 lbs per inch and you weighed 200 pounds you would compress the spring 2 inches and if the spring was 5 inches tall (uncompressed) the bottoms of your feet would be 3 inches off the ground. If you put a spacer under the spring of an inch tall your feet would be 4 inches off the ground, but the force in the spring are he same and the amount of compression is the same, but now you are an inch higher off the ground. Now if you added an inch of preload and clamped the spring to 4 inches, then stood on it, the preload goes away and the spring is still compressed 2 inches. The spring is still operating in the same range, the rate is unchanged and the forces are all the same.

B Stead

The source that I posted relates to springs on a motorcycle but springs on a motorcycle work the same as springs on a car.

In fact anyone who ever rode a motorcycle knows that increased spring pre-load on the rear shock is a stiffer ride (unless a passenger is added)
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autoxer6

Pre load is loading the spring prior to adding the weight of the vehicle. You can do this with coil overs, like motorcycles have. Adding preload put clamping force on the spring before you add the weight of the car. This does increase the effective spring weight on that corner of the car. You cant preload most stock car suspensions. There isn't a device to "clamp" the spring. All you can do is change the ride height. A comparison would be adding a block on top of the spring.

B Stead

A spacer can be used with an unadjustable coil spring to pre-load the spring.

The block that raises ride height without spring pre-load must be between the upper shock mount and the chassis and not touching the spring.

A beam axle (live axle) on longitudinal leaf springs can be spaced upward without spring preload and that for lowering the car. A beam axle on longitudinal leaf springs with front and rear shackles added would raise the car without spring pre-load. The first case is the attachment of the axle to the springs. The second case is the attachment of the springs to the chassis. In both cases nothing puts additional pressure on the springs
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Solofast

The only way that preload can have an effect on spring force is if the preload is so great that the weight of the car or bike, at normal load, does not overcome the preload. That case, as pointed out in the bike article, the vehicle would ride horribly, because the vehicle would act as if there were no springs at all, until the preload was overcome and then the springs started working. While those charts point out spring force vs TRAVEL is effected by preload, when you sit on the bike, you end up on a different point on the travel curve because the force on the spring is the same, and as they mentioned in the article, the spring rate doesn't change. Simply put, preload has no effect once you are off the extension stops, but it does effect the ride height and rebound travel which can drastically effect the ride and handling.

As you pointed out in your later post, putting spacers under a live axle or putting shackles on the spring essentially do the same thing, they change the ride height, but don't effect the spring rate. Same thing with the leaf spring adjusters on our cars, the ride height is changed, but the spring doesn't see any difference, and the spring rate is the same.

SnipeUout

Seem likes the post got a little off topic.

I was thinking about it some more and realized that if I want to run A-stock there is no way I could run Z51 gear as it was not offered for my year and even if that's not issue converting the car to a true Z51 would be extremely expensive and time consuming. Outside of doing springs, shocks and bars I'd also have to add all the coolers, the brake rotors and a Z51 transmission.

That is not going to happen. I'm starting to realize that I have no chance at competing with a GS or Z51 car that is properly driven and obviously a Z06 which has no right to be in A-stock. SS is just C7s and C6 ZR-1s.

I bought the wrong vette for A-Stock competition. I can run it sure but realistically it will need to be beefed to compete with S2000 CRs and other cars that dominate A-stock.

If I start modifying my car ill be jumping up In class and then some guy with a modded S2K will still be eating my lunch.

B Stead

Your debate style is to create perceptions rather than relate science.

But the ride height bolts on the Corvette push on the springs and that's spring pre-load
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B Stead

Well, there is a GM T1 suspension kit. And then search for the wheel sizes and offsets used with the kit since the A-arms are changed. (Probably, you can't run Z06 wheel offsets without a wide body kit.)

Or Penske shocks (direct fit available) with 150 lb springs could be used in conjunction with the stock springs. Of course the shock valving would be for the combination of spring rates
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SnipeUout

This doesnt help at all.

Could I get away with a rear bar and some Koni reds?