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Discussion Starter #1 (Edited)
While the Z06 is a BTW sports car, in comparison with some other cars (especially those begining with a 'P' or 'F') the steering is considered a little vague.

Has someone figured out a way to address this? Is the issue bushings, rack design, kingpin/caster angles, rear geometry?

Thanks,

David

P.S.
Another difference may be chassis stiffness. BMW and Porsche both use McPherson strut front suspensions. While the geometry may be less than optimal, the front is very 3-dimensional and stiff. One thing that came to mind from the Z06 pictures with the body off is that other than the drivers compartment, the frame seems to just be two rails.
 

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Although the OEM steering is not a high ratio racing rack (Lock to Lock in 180 degrees) it does have some good attributes.

Many think it is sloppy but at speed it is not. This perception comes from the fact that it is a Magnasteer unit. While it is NOT variable ratio it IS variable effort. It may seem sloppy and loose at low speed but is more resposive at high speed while not being as "twitchy" as a high ratio racing unit would be. So you can parallel park with it and drive 180 MPH.

You can improve the steering and handling. The traditional method would be to:
- Lower
- Corner Weigh
- Corner Weight
- Competition Alignment
- Install VB&P Poly Graphite Bushings
- Install Penske DA Shocks with Remote Reservoirs
- Install Baer Adjustable Spherical Bushing Toe Rod & Steering Rod Ends
- Install VB&P Extreme Springs or go Coil Over
- Custom Billet Hub & Hub Carrier are available
- Optimize tire size to Neutralize the handling
- Better wheels and tires are available for the track.

To modify the steering specifically would require reengineering or replacing the box and rack with racing componants, such as those from Sweet.
 

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Discussion Starter #3
DJ,

Thanks for your answer. So you believe the primary problem is the rack's power assist. Is the Magnasteer an electronic assist? Is it controlled by the ECU? Can it be reprogrammed?

I was thinking of the issues primarily in terms of street enjoyment. So the more extreme racing changes are unlikely.

However, is there a bump steer problem that the Baer spherical tierod ends let you fix?

Are the shocks, especially on the newer '04 and upcoming '06 incorrectly calibrated? I thought they were reasonably tuned monotubes. Do you know which piston, shim stack, and nitrogen pressure the Penske's use? Or do they custom build them for each customer? If so, do they have recommendations for different tire, track/road surface combinations?

Thanks,

David

P.S.
How would the billet hub help and who makes it?

P.P.S.
Does adding a road racing style rear roll bar help the steering. On the Porsche GT3, Autocar reported that the roll bar significantly improved handling (in one of their best handling car tests). This would result from stiffening the chassis.
 

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1. I DO NOT think there is a problem with Magnasteer or the Corvette steering. Many top Pro Solo, National Tour and T1 guys think it's great right off the showroom floor. It does have it's limitations but overall is very good. It is a Computer controlled Electromagnetic Mechanical/Hydraulic system. The Corvette uses the advanced Magnasteer II system which looks not only at A speed sensor but delta wheel speed sensor values, steering position sensors, driver input, braking, roll data and input and control from the BCM, ABS and EPBCM. It is programmable using a Tech II Analyser with Softer, Normal and Firmer selections available.
Here's a comprohensive article with the straight skinny:
http://www.babcox.com/editorial/bf/bf20224.htm

2. If a car is lowered past the factory recommendations it may increase bump steer at high speeds and with increased turning moment. Some of this is Toe Rod induced. Baer has adjustable spherical bearing bushings that allow the toe rod to be adjusted back to parallel and do not disintegrate due to rotor heat. Of course the car needs to be properly "bump steered" first.

3. The OEM shocks have been improved over sucessive years but are NOT incorrectly valved. They just have their limitations as cheap OEM units. The '04's are very good for the street.

5. Penske's come with an infinite number of shim stack combinations and can be custom tailored for each driver, car and track. However the range of adjustability in bump and rebound are usually enough to tune the shocks if they are set up correctly initially. Penske does have base line set ups for AutoX & Track. Most racers and tuners do not devulge their valving set ups as they are more or less a trade secret.

6. Billet hub carriers and hubs in Aluminum and Magnesium are available. They are used to optimize a lowered car's suspension geometry. The Corvette ones are custom CNC machined on a case by case basis. They are relatively expensive. Yes, I know who makes them. I would only recommend them on a maximally lowered dedicated track car. I can get them for you if you so desire.

7. Sway Bars DO NOT stiffen the chassis but only control Roll. They are free moving suspension pieces. Sway Bars DO resist ROLL and a stiffer bar will resist more. I would NOT just install a rear T1 bar and recommend highly against it. I might suggest installing a front T1 bar or both T1 bars depending on what the car is doing and what the driver wants to accomplish. ( I editted this for clarification as I previously thought you were confusing roll bar with anti roll bar from the context, sorry)

8. Although a Harness Bar and a Roll Bar will add a small amount of stiffness to the chassis, only a welded Roll Cage is considered stiff enough thru 6 or more attatchment points to effectively decrease the harmonics of the chassis.
 

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Hello David,

Are you still on 17" front rims ?

The single biggest improvment in "feel" was my switch to 18" fronts with 35 series Nittos.

1K miles prior to rim swap I had it lowered, cross weighted, aligned, and got a bump steer kit all done by Phoenix Performance when they did the cage install.

The setup changes made a big improvment in overall road holding, but the rim and tire swap took it to the next level IMO.
 

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Arnoldir,

Did you use the stock 18x10.5 wheels with the 305/35R18 Nittos on the front of your car? Were there any clearance issues? Thanks.
 

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DavidNJ said:
Another difference may be chassis stiffness. BMW and Porsche both use McPherson strut front suspensions. While the geometry may be less than optimal, the front is very 3-dimensional and stiff. One thing that came to mind from the Z06 pictures with the body off is that other than the drivers compartment, the frame seems to just be two rails.
The C5 Z06 I suspect is as stiff as any Porsche or BMW made during the same model year, with the possible exception of the Carrera GT, as to which I've seen no numbers. The Z has one of the stiffest-yet-lightest street car chassis in the world.
 

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Discussion Starter #9 (Edited)
DJ,

Thanks again. Even more info. I'm sure from a racing standpoint the steering is fine. However, compared to some other makes in the price range of a C6Z, maybe not that great. A recent Car and Driver comment was "Slightly robotic, insulated steering doesn’t help confidence levels."

On the shocks, I thought GM had upgraded to a reasonable quality shock. In the $50+k (and now $70+k) range, it is common for manufacturers to use Bilstein or equivalent shocks of pretty high quality.

With the Penkes being relatively common (for a $3200 shock package), I thought the standard piston and shim stack would be widely known. Of course, competitve racers can extensively customize it. Presumably at the track on a test day.

DJWorm said:
17. Roll Bars DO NOT stiffen the chassis but only control Roll. They are free moving suspension pieces. Roll Bars DO resist ROLL and a stiffer bar will resist more. I would NOT just install a rear T1 bar and recommend highly against it. I might suggest installing a front T1 bar or both T1 bars depending on what the car is doing and what the driver wants to accomplish.
I was thinking of the roll bars welded/bolted to the frame for crash protection, in contrast with the anti-roll bars used in the suspension. It looks to me that the added triangulation would significantly stiffen the Corvette chassis.

Thanks,

David
 

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Discussion Starter #10 (Edited)
Magnasteer question:

Has anyone bypassed the control unit and provided a fixed current?

Has anyone replaced the rack with a Sweet, Appleton, etc? Do the racing Z06s like LG and ALMS cars use the stock rack?
 

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Discussion Starter #11
quickZ said:
The C5 Z06 I suspect is as stiff as any Porsche or BMW made during the same model year, with the possible exception of the Carrera GT, as to which I've seen no numbers. The Z has one of the stiffest-yet-lightest street car chassis in the world.
Is there a site that has the actual torsion and bending stiffness of different chassis?
 

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Hey Arnoldir,

Which offset did you get on your 18x10.5 wheels that you have on the front of your Z? Is it the same offset as the rear factory 18x10.5 wheels? I was thinking about running the same wheels front and rear with the 285/18 Nittos up front and the 305s out back.

Stretching a narrower tire onto a wider wheel is one of the most effective ways to improve "turn-in" response, although its "breakaway" characteristics will be less gradual and more sudden... not too much of a problem on the front (understeer), but on the rear can cause twitchy "snap oversteer". Generally, a wider tire on a narrower wheel at the rear of the car will allow the car to be more easily balanced mid-corner with the throttle and will be more forgiving to drive.

This is what I have read, anyway... I'm not a race car driver, I just like to pretend sometimes. :lol:
 

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Hey Blue Angel,

I honestly just called John at CCW and asked him to hook me up with the widest 18" front and rears that would work without mods, on stock brakes. Big brakes will require new wheel centers if I upgrade.

He suggested either the Toyo RA-1's or Nittos, and I went with the Nittos to get the 285 vs 275 front and larger tread blocks.
 

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What you want is a "faster rack", a Rack/Pinion with a lower gear ratio. The Z's ratio is supposed to have been specifically chosen to improve high speed stability. While a fast rack makes the car a little "snappier" at low speed, it makes it considerably harder to control at high speed. "Over control" becomes a problem and car gets "twitchy".
 

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Discussion Starter #15
Without going into detail about from who, I've been told that he new C6Z has the same steering 'issues' as the regular C6. From someone who has driven both, including some limited track time. At least limited in the C6Z.

This is not to say the steering is bad. Just not as good as some of its competition. And what I was wondering is has anyone addressed that 'issue' and if so, how.

It is a matter of feel rather that ratio, although slow steering could be an issue (as it is in most MBs).
 

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As another reference point, I also had some work done on my car at Phoenix. The suspension work done includes '04 shocks, lowered, more aggressive alignment, poly bushings, adjustable end-links, and corner weighted. I use 17" wheels for competition. The car is a lot more responsive to steering inputs. I can't say what did it as everything was done at the same time. My point being: I think with some upgrades, you may be able to achieve what you are looking for (maybe not). You may have to make some trade-offs though. I feel the bumps a lot more now.
 

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Discussion Starter #17
MySR71,

Sounds interesting. What alignment setting did you have before and after the change?

It sounds like you have a stock (or at least OEM street) shock/spring/anti-roll bar package with lowering/alignment/bushings. Were the end-links for the anti-roll bar or the tie-rods?

Thanks,

David
 

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Sorry for the delay in getting back to you. My previous alignment was factory stock, the current settings are:

Front
camber -1.0
caster as high as possible
toe 1/32 out

Rear
camber -.5 to -.7
toe 1/8 in

The shocks are from an '04 Z06, stock 2002 Z06 sway bars with poly bushings, stock 2002 Z06 springs. Poly bushings on the control arms on the front and rear.

The endlinks are on the sway bars so that the car can be corner weighted properly. The endlinks are from LGM are are teflon coated. They are significantly more expensive than the non-coated version but don't make any noise.
 

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You know, just reading about the C6 06 options, I realized that a smaller steering wheel would change the ratio. The 06 has a 9.4" wheel, which they must have added for precisely this reason.
 

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The smaller wheel will reduce the hand movement arc a bit, but I think the actual degree of wheel rotation or input required to obtain a given response would remain the same.

There are a couple issues with the steering- the relative lack of feel and the steamboat slow ratio. Coming from a more responsive, shorter wheelbase, 13.3 to 1 Z51 C4, I've searched for a quicker rack or other options to the standard 16 to 1 since day one. The car just feels sluggish and unsportcarlike.

This is the only alternative I've found so far:

http://www.howeracing.com/Steering/Index-Quickener-Quickener.htm

I'm not sure a quicker rack necessarily alters car behavior at speed, although it may accentuate inherent problems if drivers do not adapt to it. When the C6 debuted, I asked Hill if they'd tried a quicker rack, and he said they had, but it made the car too 'pointy.' Sounds like they just took the easy way out and did nothing.

The cars seem to be built basically for one type of driver and one type of driving, and everybody else has to make do.

It'd be nice if the new wheel would retrofit to a C5, but that seems unlikely.

Sorry if this isn't pc.
 
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