Oversteer

[Zfun]

Unlike most cars made for the street, the Z has a very noticeable tendency to oversteer when shifting (or just lifting the throttle) mid-corner. I have gathered in talking to other C5 owners that they too acknowledge this problem once I ask them about it.

I am not looking for an education in "trailing throttle oversteer", "moments of inertia", lessons on how to drive or not drive. This is a very bad trait for a street car and is unacceptable at street legal speeds. Has anyone ever researched this and come up with a solution.

Alignment issue? Tire pressure issues? Locking differential issues?

 

[atmmac]

i never really noticed it.

 

[c4c5specialist]

HI there,
A few questions, please.
Has there been any work done to the vehicle???? Driveline, suspension or the like??? Aftermarket shocks????
Also, I would definately check the alignment, as it should be at least verified that the settings are correct once a year.
Please keep us posted, c4c5

 

[Zfun]

c5d,

Yes you did miss something, you missed the part where I kindly asked for no driving lessons. I pay for those. You also missed the fact that these are streets speeds. EVERY car I have owned up until has not acted like this, not to this severity. On the street it is impractical to, at some point, not to shift while rounding a bend, IMPRACTICAL.

So you agree that yours does the same thing ??

 

[Zfun]

c4,

No work that I can tell (I bought the car used) everything appears to be factory. The alignment was recently checked and reset to the updated 2002 specs that came out for the Z06. The problem is a little more prominent turning to the right than to the left. Here are the current specs, all very close to nominal:

Front: ........................... Rear:
Toe -.04L -.04R ...........+.02L - +.03R
Camber -.7L -.5R ......... -.5L - -.9R
Caster 6.7L 6.5R

The car seems sensitive to tire pressures and changing to 30psi front and 34 rear has helped. Should I try a bigger spread ?

My local GM tech here agrees that says that the few c5's he has driven have exibited this trait. The alignment tech (a different guy) is out for 2 months so I will be unable to pick his brain, apparently he knows a lot about the idiosyncracies of this car.

Let me know if you see anything here. One question I am trying to put to bed is regarding the differential. I have been told the c5 differential lockup is controlled by the ECU. Is this true ? My local tech says know (actually "I don't think so"). If it was was it would explain away every bit of this.

Thanks in advance, Z

 

[VETTEX2]

Toe in the rear until you get the car tight.
I prefer loose but not excessive looseness.

 

[Zfun]

c5d,

Unfortunately boards like this inherently bring out "self proclaimed" driving experts and your comments immediately said nothing of mechanical issues but rather driving issues, hence my response.

I'm glad to here that your ZR-1 doesn't exibit this trait, that's a good sign. Unfortunately I have found too many C5's already that do. 4 out of 6 so far, 2 of which were Z06's. Driving this car on the track in it's current condition, where all turns are planned, would be much less a handful than on the street.

I agree manufacturers build in understeer for those situation I mentioned in my last post and the situations you mentioned. The Z too has plenty of understeer in a steady state situation near the adhesion limits.

I have no problem handling the Z the way it is now, however I worry more so about my wife even though I have already demonstrated this trait to her. It's dangerous especially to someone unsuspecting, and god forbid you add a little rain. Finally I don't think using the AH as a crutch isn't the answer either (except in the wet). I prefer to drive the car raw, learn it, then add the AH at some point at the track. Then you know the car.

Right now something is amiss.

 

[Zfun]

VetteX2,

Any numbers for a starting point?

 

[trumperZ06]

Y'all might want to look at a posted thread by someone called Silver Streak in Canton, Ga. The title is "High Speed oversteer" in the Pit Road section, and seems to be simular to this one! If its an issue with the car's mechanicals, take it to a dealer!

The rear end is NOT electricly controled by the ECU or other systems! This is a standard mechanical unit found on many high powered rear wheel drive cars.

 

[c4c5specialist]

HI there,
I would have your tech check the steering axis inclination first of all.
Setback should also be referenced.
As far as your settings, they seem fine, not optimized, but within specification.
Please keep us posted, c4c5

 

[trumperZ06]

Y'all might want to look at a posted thread by someone called Silver Streak in Canton, Ga. The title is "High Speed oversteer" in the Pit Road section, and seems to be simular to this one! If its an issue with the car's mechanicals, take it to a dealer!

The rear end is NOT electricly controled by the ECU or other systems! This is a standard mechanical unit found on many high powered rear wheel drive cars.

Go to www.Z06Vette.com for this thread! Then go to the "Pit Road" section to look up the posts!

 

[Rob]

c5d,

Unfortunately boards like this inherently bring out "self proclaimed" driving experts and your comments immediately said nothing of mechanical issues but rather driving issues, hence my response.

Actually, in my opinion, his questions were legitimate, and it's my interpretation that you're unfairly reading in to his questions/posts. Chill out....nobody is here to question your driving technique or mechanical knowledge. I think he's just trying to help.

 

[Rob]

Re: No need to take this post any further..

The thread I posted is fairly enlightening. Out of five forums no one is having "his problem" and those who actually are testing their Z's, none come back to report any propensity to oversteer. Just the opposite in fact ( i.e., RC45, Z06 Senior Member's response at the bottom).

The tell tale thread clearly shows the fact pattern changes as the threads progress.

When he's ready to post his picture with a Z06 and explain why the fact pattern changes when he's Silver Streak, I may reconsider. Until then, there are other folks who I prefer to help out.

JMO
C'ya
D

Dann,

Just so we're clear, my response wasn't directed towards you.

-Rob

 

[leaftye]

I really don't see the oversteer as a problem. I'd much rather have a touch of oversteer than to have understeer. I find it to be more fun, and easier for me to control. I apply power oversteer ALL the time.

I learned the hard way on my first car about how dangerous lifting the throttle in a corner could be in a 93 Formula, and I paid for my indiscretion by way of a totalled car.

The oversteer is pretty normal. We have cars with big engines, and these big engines have lots of engine braking torque associated with them. Lifting the throttle is pretty close to pulling the e-brake...so it's braking with the rear wheels only. If you must lift the throttle or change gears in the corner, do so very carefully. Shifting thru a corner can be done, I do it, but usually I shift going into the corner. I have a front wheel drive 89 CRX, and shifting in a corner is even more tricky, but when I drive the thing properly, I can put it in the proper gear and have my understeering prone car go thru a corner in a sweet four wheel drift.

I know you don't want a driving lesson, but you have to accept that our engine are also brakes. Ask a semi driver about engine braking if you don't quite understand yet. If you insist on shifting mid corner, you'll need to spend more money on learning how to drive like you mentioned, or wreck a car like I did.

 

[Zfun]

Well it looks like I stumbled on a click here and I'm amazed how TWISTED this thread got. And since c5 said "let the games begin", Here we go:

Rob I did not find c5's comments relevant, and I stand behind that. I thought I was very specific about what I asked, apparently not. He obviously took offense to my comments but he gave nothing tangible. I'm very curious how and where my facts changed c5 or how you can assume I'm Silver Streak ?????????

I have checked out the thread Thumper mentioned and have since talked to Silver Streak, and will be meeting him to take a ide in his Z. He thinks he has the solution and it sounds like an alignment issue similar to what c4 has mentioned. I have to thank Thumper for that even though I believe that was not his intent. BTW Thumper thanks I would have never thought to take my car to a dealer. I guess you too didn't read my posts.

Many thanks to those that offered up comments about how their cars react and those with mechanical feedback or suggestions. Atmmac, c4, VetteX2, and Leaftye. Your responses, in particular c4, have been very helpful.

 

[BlackMagic]

Z,

I just found this board and stumbled on your thread while surfing. I went through the same thing about a year ago. Some people have the problem and some don't but it does exist. Some have it and are used to it. Mine would also pull slightly to the left in a straight line under heavy power. If yours does the same I think I have a solution.

The issues are mainly with the rear alignment and possibly with the steering axis inclination as c4 mentioned. I don't think there is anything drastically wrong. The geometry of the car really lends itself more for the track and if these alignment issues go too far one way they can create some not so friendly responses on the street. Your car would probably handle fairly well in it's current condition on the track.

I will send you an email so we can speak directly.

Hector

 

[RedRagTop]

Relax. I remember a thread here a while ago pertaining to a guy loosing his new C5 on an onramp or something because the ass end came around on him, I think it was called OMG! The worst thing happened or something like that.

 

[trumperZ06]

1st Clue...

Well, since 1997 I have only heard of ONE... or is it now TWO people... who thought that the limited slip rear end was controled electricly by the ECU !!! Any one with track experience... KNOWS BETTER!!!

2nd clue... simular tone and a chip on the shouder about ... having "expert driving abilities" are in both threads! What we have here is... A legend in his own mind!

I suspect its possible that... Y'all may have a mechanical problem! If so, then a Chevy dealer with an acredited Corvette Mechanic, Maybe Tom Jumper... ask for their corvette mechanic "Dave", would be a logical choice to solve the problem!


IMHO Having owned a C5 coupe and two Z06's, and tracking both Z06's regularly, if the cars are mechanicly sound, they handle exceedingly well!

Others who also track their vettes have also been happy with the on track performance.

There is nothing wrong with the suspension's design with properly functioning parts, that would cause a properly driven car to handle as you describe.

If your vette has a mechanical problem it needs to be identified and repaired. These cars are set up to UNDER-STEER, as delivered from the factory, and the active handling steps in to compensate for driver error.

 

[leaftye]

Z,

Mine would also pull slightly to the left in a straight line under heavy power.

I've read that cars in this hemisphere almost always go sideways in the same direction, and the opposite direction in the other hemisphere. It's like when you pull the plug on a sink full of water...the water will always swirl down in the same direction.

Another thing to consider is that almost every differential is stronger on one side than the other. There are different types of differentials, and some do lock the axles while going in a straight line. I'm not sure about the differential in a C5. The axles are also different lengths, with the left one being longer, more prone to breakage, and that wheel bearing also fails more often.

Cars with longer wheelbases are less prone to swapping ends, and the next Vette will have a longer wheelbase. Note that the first gen Viper was very prone to swapping ends, and that it had a very short wheelbase.

Some people complain about the rear end hopping sideways when they hit a bump in the middle of a corner. That's a whole different problem, and an autocrossing team seems to have a solution. They have a direct replacement rear tie rod bar set that's supposed minimize this problem.

If you'd like to change the handling of the car to make it understeer more, and oversteer less, consider modifying the swaybars. At the very least you'll need adjustable end-links, but I'd just opt for swapping out the sway bars. You'll want a stiffer bar on the front end. This will cause the front to slide more. You can even swap your Z06 rear sway bar for a base suspension rear swaybar. Do both and you should have a car that understeers BIG TIME!

I recommend playing some racing games like Gran Turismo and changing the suspension settings to get a feel for how the changes will affect the car. It isn't precise, but it'll give you an appreciation for how modifying suspension settings will changing the handling characteristics of the car.

 

[Chalky]

if I am reading your rear toe settings correctly, you are running with toe out. If that is the case, that would definitely contribute to oversteer.