I have a Yellow, 3LT, fully loaded, 06 Z51 that I just upgraded with all factory GM parts including Z06 wheels, tires, fenders, quarters and brakes. It still has Z51 sways and shocks. I lowered it all the way on the stock bolts which insn't much.

On the tight twisties the car handels great and slides just a bit in the rear if I push it hard around corners with no active handling involvement which seemed a little strange to me (compared to my C5). I can get over 1 G on the meter. However on the long fast sweepers like on ramps at .6 or .7 Gs the traction control comes on and slows me down at speeds I know the car can handle, in fact at speeds my old C5 could have handled.

So my question are.

1. What is going on
2. What will adding the rear Z06 bar do for me
3. Would Bilstiens make much of a difference

I know that 400 of you are going to ask why I didn't buy a Z06 instead. Well for those of you that want to know why. 3 main reasons in order of importance.

1. No automatic which I have to have.
2. No removable top.
3. Didn't feel like paying 10K over list and I needed the car right now becasue my C5 died.

This is the tech section so please don't plug this thread up with all the garbage about fake Z06s and stuff, I realy don't want to hear it. If you would like to complain please post a thread called "fake Z06 haters" then you can all go there and complain.

Future mods inclued LG headers, Z06 exhaust, z06 battery relocation and eventualy supercharger and related mods.

By the way it's yellow, has chrome wheels, tinted windows and looks absolutly stunning.

My only complaint is the horrible sound of the XM.

I have owned a 82, 94, 96, 00 and now my 06. Oh my gosh what an upgrade from the C5.

 

Man you have a lot going on. First and I'm no expert and my comments are meant purely as support, but as you know suspensions are packages. I know GM spends many days on test tracks tuning all the components. Some parts can be changed without adversely impacting or upsetting the cars balance and in fact actually improve a cars handling. Just watch a NASCAR race and you'll hear them talk about a 1/4 of air pressure and how it affects the handling. So making all the changes you did will have some impact on handling. You probably found the combination that doesn’t work. Now just what that is is anyone’s guess.

I changed the rear Z51 sway bar for the Z06 (my ONLY suspension mod) and I personally like how the car feels. Some of our "so called" experts have cautioned me that I upset the balance of the car so much I'm "an accident waiting to happen". I guess you could change out the sway bars and maybe shocks, but once you lower a car and start modding it's suspension you entering the "twilight zone" as far as facts are concerned.

Having said all this, I can only hope some REAL experts with a technical background will offer you the advice you seek. I can't. I’m going to monitor this thread to see what advice is given.

Good luck.

Tom

 

 

This raises the question of whether active handling control inputs are based off of a 'look-up' table based on the stock suspension level (base/Z-51/F-55/Z06) mixed with sensor input of speed/lateral G. I don't think you're going to get a complete answer here unless a GM engineer chimes into the thread.

 

I upgraded the base sway to Z51 and dont have traction control kicking in on sweepers so not sure what should be made of it but makes me wonder about it being a look-up as stated. Not saying you said it was so, smake charmer, nor that it is or isnt, just throwing the data point in. Obviously the fenders and are not part of the equation and many have put on the Z brakes and I havent seen anyone post about this causing an issue with active handling. Seems like it would come down to the wheel/tire combo or lowering. Again lots of people have done both and I dont recall seeing a post about active handling issues. Be checking back on this one to see where she goes.

 

The car will slide a little bit before AH kicks in. That is how it was designed to function, while the full AH mode on the C5 was more intrusive. Lowering it slightly will not screw up TC/AH. Plenty of people have lowered their cars even more than you have (myself included) with no issue whatsoever.

In your situation I'm initially suspecting tire sizes. Are the tire diameters the same, or very close to stock? I know you can change them slightly and still be ok, but any differences will be magnified at higher speeds, which correlates to your troubles in fast turns.

Despite the extra weight of the Z06 wheels, tires, and brakes, that should not interfere with AH. The springs, shocks, and sways may no longer be as stiff to respond the way it used to, but AH doesn't look at suspension movement, it looks at the speed each wheel is turning at, along with the movement of the entire car. Are you getting a lot of body roll? I don't know if that is measured but something to think about.

In the back of my head I want to say that alignment may come into play as well, but really cannot think of how that would be a factor, unless it was causing some instability which would probably be noticeable to you. Although it is something I would have set anyway, unless you're waiting to do more suspension changes which will require that. But unless the car doesn't feel right during those maneuvers, I would not worry about the shock/spring/sway bar rates as the cause of this problem.

 

well i have lowered my z51 all around and went with hotchkis big red sways and it has made a whole new car out of it. But as far as the on ramps and the traction control and active handling coming on it is because they dont want you to hit a wet spot and have you go sideways and lose it. Because the average corvette driver doesnt even take the car to its limits with the traction control on.

 

It is important to understand what suspension pieces do, esp. the swaybars. When you stiffen one end of the car and leave the other end unchanged, you cause the stiffer end to reach the traction limits faster, which means that end will break traction sooner than it did before. So if you already have more oversteer than you wanted with the Z06 wheels / tires, adding the stiffer Z06 rear bar only will just worsen the problem (more oversteer).

If you want to tame the rear, you need to put a stiffer front bar on.

The amount of roll stiffness, front to rear, is known as the roll couple distribution.

That said, I am not sure why you have the issues you have, assuming your Z06 wheels are the exact same as the OEM (275/35/18 front and 325/30/-19 rear). Your grip coefficient is the same with the Z06 wheelset, and so is the rear/front diameter differential, which is what affects TC. So the car's behavior from this should be no different.

Maybe you are just pushing the car harder than you were before and don't realize it.

The other possibility is that you altered alignment when you lowered it.

 

I could not agree with you more. I flipped a car at Blackhawk Farms in South Beloit IL, because I changed the back and did nothing to the front. That was 30 years ago, and I won't make that mistake again.

 

For question #1:
The software for the Stabilitrack was calibrated for the stock wheels and tires.

 

1. Good question. TC happens when one or both rear wheels are slipping while AH is looking at slipping, braking, speed, car angle, and, front wheel position. I would think you would see AH warning rather than TC on a .7g sweeper, unless you are hiking the inside rear wheel off the ground. If the inside rear is hiking off the ground then it is spining at least long enough to trigger a TC warning.

2. If the inside rear wheel is hiking because of too much traction on the outside coupled with excessive body lean, the Z06's 1.25 bar should cure the hiking. The Z06 front bar is the same as the Z51 bar.

3. Bilstiens or Z06 shocks may or may not do much for prolonged sweepers, but reports from forum members say the Bilstiens offer better high speed handling.

I replaced my Z51 rear bar with the Z06 bar because I didn't feel comfortable with the rear inside lift on 90 degree turns. As a bonus, it made oversteer more predictable and seemed to tame those surprise 360's

 

Have a Z51 and also upgraded to hotchkis sways plus bilstein sports. Unbelievable package! This is the way to go!

 

Did you do the upgrade at the same time? I would like to know the difference between the car with just the bilsteins and bilsteins + hotchkis.?

 

Same time. I've liked the handling/corning/road feel of my M3 better than my vette. No longer!!! This setup is perfect. Much more control of the car and more confident at it's limilt. Not harsh at all. I also updgraded the tires to 325s in rear and 275s in front. I get slightly more understeer but all in all I could not be happier.

I've had 2 forum member ride/drive in the car and both commented how civil and stable the setup is. It's a winning combo

 

I have not touched the shocks, sways or springs its still all Z51. The brakes, wheels, tires are all factory Z06 parts right down to the Goodyear F1 Supercar EMTs in 285/325.

I just realized that I haven't programmed that new TPSs yet since I changed the wheels. So they are not reading correclty. Maybe that is the problem? Any comments on this?

For those of you that mentioned incorrect tire sizes, are the Z06 tires larger in diameter than Z51? I just shipped my old wheels and tires today so I can measure them.

Vararam showed up today and Z06 mufflers will be here next week.

I am having a blast with this car. With my chrome wheels, tinted windows and lowering this car is hot. I only have been driving it for a week and you would not believe how many comments I get on it every day. I have about 100 employees and about half of them have stopped by to tell me how hot my car looks, everything from High 5s, handshakes and congrats. Dam its like I got married again or had antoher kid.

The best part is getting away from work and just tinkering in the garage. It's like therapy, every stressed out CEO needs a Corvette to work on after hours, almost as good as sex.

RD

 

Oh one more thing. Understeer is when the front end pushes out correct? Oversteer is when the back end slides or do I have it backwards?

Where did you get the hotchkiss/Billstien kit and how much was it?

 

I think you can get both at http://www.ajusa.com/cgi-bin/store/start?r=store&

I have the bilsteins and by far its the best thing I've done for my car!

 

Yea you got it right.

I must agree with you. Often after working on the car I feel happy and satisfied, even though I didn't even drive it.

 

Would adding just the Z06 rear bar alone to a new Z-51 be a smart or dumb thing to do??