GXP FE3 Suspension not the FE3 from ZOK as advertise by GM

[LatinVenom]

Reason for the thread name and the fact that I am still very disappointed at the overall handling of my GXP even with the Eagles F1's GS-D3's.
This link:
Gxp Z0k?

a quote from it:

Astocker,Everyone I just finished filming a TV show with the GXP for Speed Channel (today) (buildorbust.com click trailers "SETUP") I had access to the GM Performance guys (multiple guys/prat&miller/Lutz/Sitek Ect... The big guys in Charge of everything Solstice, so to speak. The GXP Does not have the ZOK shocks and springs, in fact for the show we swapped the stock springs out with the club sport or ZOK springs per GM Performance division. The GXP is heavier on the nose as most of you know and the ZOK springs really let the front drop. When the GXP ZOK comes out later this year it will most likely have redesigned front springs for the heavier nose but the rears will probably remain the same as the ZOK (ClubSport). Meanwhile check out speed channel on April 18th at 8pm to see a new show called "setup" you'll find a few recognizable autocrossers kicking some butt. :-)) Kevin 2006 CS National Champion

Another quote this time from ASTOCKER:

The thing I learned from Ron and Kevin is that the car really needs those springs from the Z0K package. When I bought the car I was told they were the same as on the the GXP: they are not. I think having them would make a fairly big difference.

Based on the above I wrote the following part numbers from my GXP, can SD, SM or Windface verify that these are suppose to be the parts numbers for a GXP suspension and if they check out are these the part numbers for a FE3 suspension parts THANKS.

REAR SWAY BAR #15224878
REAR SHOCKS BILSTEIN #C648
REAR SPRINGS #15784886
FRONT SWAY BAR #15224873
FRONT SPRINGS #15784872
FRONR SHOCKS BILSTEIN #C646

[51gxp]

Originally Posted by LatinVenom Reason for the thread name and the fact that I am still very disappointed at the overall handling of my GXP even with the Eagles F1's GS-D3's. This link: Gxp Z0k? a quote from it: Another quote this time from ASTOCKER: Based on the above I wrote the following part numbers from my GXP, can SD, SM or Windface verify that these are suppose to be the parts numbers for a GXP suspension and if they check out are these the part numbers for a FE3 suspension parts THANKS. REAR SWAY BAR #15224878 REAR SCHOCKS BILSTEIN #C648 REAR SPRINGS #15784886 FRONT SWAY BAR #15224873 FRONT SPRINGS #15784872 FRONR SCHOCKS BILSTEIN #C646

Great inquiry, LV. I'll be real interested to see what you find out. You may finally have hit on why the car hasn't handled to your expectations since you got it. As we've discussed in the past, I'm very happy with my cars overall performance window, but I have no where near the same experience of sports car ownership that you have, nor the frame of reference of having been a NA Sol owner too.......

[mena661]

It really wouldn't surprise me if the FE3 on the GXP differs from the FE3 on the Z0K's. When I took the car home I really couldn't see how the stock setup was good enough for the racers to do their thing when I really didn't like it just driving on the street. Nice one LV.

[SolsticeMan]

I can confirm that C646/C648 are exactly the same for Z0K w/ FE3 and GXP w/ FE3, and the sway bars are also identical p/n. Unless they changed something in the last month.

Front and Rear springs - I have an e-mail in on confirmation, but they are different part numbers. HOWEVER, the only difference is supposed to be in free length/load, and same linear spring rate (FE3 springs (Z0K and GXP/RedLine) (front and rear) : 170 lbs/in and 225 lbs/in).

The Z0K, when properly setup, sits about 1/2" lower than a GXP. (Putting Z0K springs on a GXP would result in a GXP that is even lower yet.)

The 'load' of the spring is not specified in 'free length' as I am used to, it is expressed in a 'check load' at a given height, which I don't exactly know.

It is not out of the realm of possibility that some of the difference felt is the difference in carrying height/center-of-gravity height between a Z0K and a GXP. Changing this changes the, 'roll gradient' and 'load transfer'.

HTH.

[Small Dealer]

Originally Posted by SolsticeMan I can confirm that C646/C648 are exactly the same for Z0K w/ FE3 and GXP w/ FE3, and the sway bars are also identical p/n. Unless they changed something in the last month. Front and Rear springs - I have an e-mail in on confirmation, but they are different part numbers. HOWEVER, the only difference is supposed to be in free length/load, and same linear spring rate (FE3 springs (Z0K and GXP/RedLine) (front and rear) : 170 lbs/in and 225 lbs/in). The Z0K, when properly setup, sits about 1/2" lower than a GXP. (Putting Z0K springs on a GXP would result in a GXP that is even lower yet.) The 'load' of the spring is not specified in 'free length' as I am used to, it is expressed in a 'check load' at a given height, which I don't exactly know. It is not out of the realm of possibility that some of the difference felt is the difference in carrying height/center-of-gravity height between a Z0K and a GXP. Changing this changes the, 'roll gradient' and 'load transfer'. HTH.

Will confirm what I can of what SolsticeMan has posted, based on the recently released March parts catalog.

The sway bars numbers posted are the correct ones for all 2006-2007 FE3 suspensions. While those are not GM part numbers for the struts, all 2006-2007 FE3 suspension use the same stuts. There is a difference in part number for the springs. The 2006 FE3 and 2007 FE3 Z0K are different then the 2007 FE3 Turbo GT (GTA) spring.

The sits lower parts makes sense as (at least) the 2006 Z0K Solstice was built with a second spring seat for manufacturability and shipping reasons.

[LatinVenom]

Thanks guys,
But it looks to me that GM needs to re address the springs on the GXP, the more I push this car the less confident I feel, it just wants to brake loose from the back and comparing it to the OLD NA and other cars it just seems to be tail happy.
With the OEM tires they use to skip, with the GS-D3's it grips but then you get the sensation of the tail coming loose if you push any further, which it should not happened with the tests I am making, the OLD NA stayed more planted and so does other cars.
SM, I can understand about the springs length and load but the GM engineers should have adjusted them to behave on the GXP like it's counter part, but something is off, at least to me.
Thanks for the info, maybe if an engineer from GM is reading this and some of the comments made on the link I posted could shed so light on this issue.
I want the overall performance of this car to equal its handling, and that is not happening.

[51gxp]

Originally Posted by LatinVenom Thanks guys, But it looks to me that GM needs to re address the springs on the GXP, the more I push this car the less confident I feel, it just wants to brake loose from the back and comparing it to the OLD NA and other cars it just seems to be tail happy. With the OEM tires they use to skip, with the GS-D3's it grips but then you get the sensation of the tail coming loose if you push any further, which it should not happened with the tests I am making, the OLD NA stayed more planted and so does other cars. SM, I can understand about the springs length and load but the GM engineers should have adjusted them to behave on the GXP like it's counter part, but something is off, at least to me. Thanks for the info, maybe if an engineer from GM is reading this and some of the comments made on the link I posted could shed so light on this issue. I want the overall performance of this car to equal its handling, and that is not happening.

Looks like you've got something here, LV. As was stated by a previous poster, could the handling problem you describe be caused by the difference in weight distribution of the GXP vs. the NA Sol? And might it be improved by putting the lowering springs on? Different sway bars? Larger footprint rear tires? It will be very interesting to see how the GXP is set up for racing by GM. I know most of us wouldn't want the rock-hard suspensions that racers use, but certainly ratios of front/back sway bar diameters, spring rates, and tire footprints may be useful information. Sure is interesting that it appears that GM released the GXP with lower handling thresholds than the NA Sol

[LatinVenom]

The problem seems to be in the back and not the front, and since the sway bars are the same I would not think they are the issue, same thing with the shocks, but maybe 255 or 265 or 275 may help not sure at this point, but certainly the springs need to be address IMHO.

[51gxp]

Originally Posted by LatinVenom The problem seems to be in the back and not the front, and since the sway bars are the same I would not think they are the issue, same thing with the shocks, but maybe 255 or 265 or 275 may help not sure at this point, but certainly the springs need to be address IMHO.

The fact that the sway bars and shocks are the same is exactly my point. The GXP is front heavy compared with the NA Sol. Therefore to reach "similar" handling results I think it reasonable to assume something (shock, spring, sway bar, tire width) should be different

[Krazed Kanary]

Having AXed our GXP on Azeni 615s (the softest street tire out there) and on Hoosier A6s, I can say with certainty trying to evaluate handling by running on anything but race rubber or by butt-o-meter is worthless, the car is a completely different animal on race rubber.

[LatinVenom]

Originally Posted by 51gxp The fact that the sway bars and shocks are the same is exactly my point. The GXP is front heavy compared with the NA Sol. Therefore to reach "similar" handling results I think it reasonable to assume something (shock, spring, sway bar, tire width) should be different

51GXP:
The sway bars on the GXP are different from the N.A. Solstice, but are the same as the ZOK.
By the way in my case the problem is not in the front but the back, and I think at least the springs should be look into, and as you say maybe larger tires, the sway bars I think are fine for both cars and I would venture to say the shocks as well, but this is my opinion so someone like SM or one of the guys that have driven both can probably have a much different opinion.

[Miles@tirerack]

LV,

If you think the car oversteers too much you can fix that by a number of means.

The following is an excerpt from Air Pressure for Competition Tires from Tire Rack's Tire Tech section.

Guide To High Performance Handling

Adjustments...................Decrease Understeer......Decrease Oversteer

Front Tire Pressure...............Higher..................... .........Lower
Rear Tire Pressure................Lower..................... .........Higher
Front Tire Section..................Larger................... ..........Smaller
Rear Tire Section..................Smaller.................. ..........Larger
Front Wheel Camber.............More Negative..................More Positive
Rear Wheel Camber..............More Positive....................More Negative
Front Wheel Toe....................Toward Toe-Out................Toward Toe-In
Rear Wheel Toe....................Toward Toe-In..................Toward Toe-Out
Front Wheel Caster...............More Positive....................More Negative
Front Springs........................Soften............. ................Stiffen
Rear Springs.........................Stiffen........... ..................Soften
Front Anti-sway Bar...............Soften (Thinner)...............Stiffen (Thicken)
Rear Anti-sway Bar...............Stiffen (Thicker)...............Soften (Thinner)
Weight Distribution.................More Rearward................More Forward


First I'd try dropping the pressure on the front tires 5spi and increasing the pressure in the rears by 5psi, giving you a 10psi difference front to rear. If this starts to give you the results you're looking for you can step up to these changes that may give you bigger dividends.

Increase the rear negative camber (I'd start with half a degree).
Increase the rear tire section width. (You'd have to get a wider rear wheel to do so safely).

Those 3 things should make a very significant difference.

[LatinVenom]

Miles, thanks for the info above, but my problem is the way GM advertise the GXP.
My 1st 1K with F1 GS-D3's should NOT handle better or out corner my GXP with the same tires on the same test places, but it does.
There is something definitely wrong with the stock FE3 suspension on the GXP, it should be better than my OLD car.
It has larger sway bars better shocks but either the springs or the factory alignment makes it have more oversteer than the OLD 1st 1K, and that car was not even a ZOK.
I thought by upgrading to the Power of the GXP whit the FE3 suspension would give a win win situation since the only thing the N.A. car was lacking was the power, but instead I got a GREAT power performer but a not so great handling.
All I want is for GM to address this issue, I do not care if I have to buy new suspension components, i.e., redesign springs.

[mena661]

All I want is for GM to address this issue, I do not care if I have to buy new suspension components, i.e., redesign springs.

I am considering installing the GMPP springs but I don't know if I can buy those seperately. Also, some of those 18x9" OZ wheels with 265 Bridgestone RE-01R's and a more aggressive alignment should do it for me. I've never driven a NA Sol but I agree on the car not handling or gripping as well as it could but I honestly expected that.

[51gxp]

Originally Posted by LatinVenom Miles, thanks for the info above, but my problem is the way GM advertise the GXP. My 1st 1K with F1 GS-D3's should NOT handle better or out corner my GXP with the same tires on the same test places, but it does. There is something definitely wrong with the stock FE3 suspension on the GXP, it should be better than my OLD car. It has larger sway bars better shocks but either the springs or the factory alignment makes it have more oversteer than the OLD 1st 1K, and that car was not even a ZOK. I thought by upgrading to the Power of the GXP whit the FE3 suspension would give a win win situation since the only thing the N.A. car was lacking was the power, but instead I got a GREAT power performer but a not so great handling. All I want is for GM to address this issue, I do not care if I have to buy new suspension components, i.e., redesign springs.

Dang LV, you of all people here should understand what's happening..... As was established months ago, the weight distribution of the NA Sol is better than the GXP. Combined with lower weight and less power, it is reasonable to expect the NA to be faster in a static "weave" than a GXP. In order to alleviate this, simple changes need to be made (springs, shocks, sway bars, tires, or combinations of the above.....)