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

[RobL]

Originally Posted by birdliver After a few weeks of driving the GXP initially, I shook off the initial denial I was suffering from regarding mainly, the car's handling in turns. I kept telling myself initially that the new power might be overwhelming me (It was a huge change, obviously) or the tire selection could still be wrong etc., but I finally felt after going back and forth driving the N/A a few times that I had become familiar enough with the GXP to suspect that some characteristic of the new car was responsible for it not at least equaling what I was getting from the base car. I didn't notice individual things that felt wrong, but I was clearly no longer tracking through turns like I was on rails and I wasn't getting back the info that the base car was providing and so I felt less confident and the GXP felt less predictible in the turns. Nothing in particular felt different or wrong that I could put a finger on. Included in the "not tracking/no go cart" thing was that it had been replaced with a bit of roll (no way in the base car) and a feeling of less control that I didn't get at all in the other car either. I still don't know if the less communication idea is tires but LV is making me think maybe not, unless other solutions prove better than his tires or mine (I'm still OEM), I hope so. In terms of shedding some light on the subject, if someone with the capacity, time and place could conduct some comparisons between the two cars maybe some determinations could be made and some solutions provided.

Did your original car have the clutch diff? Going from a car that didn't have one to a car that does have one would explain everything that you describe (this is why the Elise originally did not come with a diff). FYI, the diff tries to keep the car pointed straight by making the rear tires move at the same rate. It feels different than an open diff that has no such restriction so the open diff allows more turning freedom.

[mena661]

If you really want true Sports Car experience, come on out to an autocross or track time trials. I sure would like to see a few more GXP's out there running so we could truely evaluate and wring out it's potential, we have only just begun.

Why? So I can go around and tell all the untrained that they shouldn't be driving their cars unless they have some track time? That they should garage their vehicles until it's "safe" to drive them? Please!! I know people that could clean your clock and they have never told people that they shouldn't be driving their cars or that they don't know anything about their cars handling. They DO encourage track driving and it IS seriously fun (never AX'd but have done a few HPDE's). The more comments I hear like this the less inclined I am to hang out with other forum members.

[ender]

Regarding Tail Happiness of the GXP... I'd prefer this over understeer. But yes, check alignment, tire pressures, etc.

The guys in the E36 M3 BMW world swap the stock staggered tire config (225/245) for a symmetrical config (235/235) to reduce understeer. If oversteer is really a problem on the TurboSol, one can do the reverse and add staggered tires. But typically, manufacturers shoot for a nice, safe, benign understeer.

And on factory alignments... sure, I wouldn't be surprised if they have the fastest and most expensive aligning system known to man... but remember, they're GM. They'll have someone slap the car onto the rack and knock out an alignment somewhere within specs in the quickest time possible. Quality is determined by tools and technique... the latter being the bigger factor.

I'd love to see a compilation of factory alignment specs. I bet they're all over the place. Maybe I'll take mine in before I install springs just to see where the factory put it.

Russ

[LatinVenom]

SM.
The tires are the same on my GXP as the one one the original 1st 1k and the same size.
Eagles F1 GS-D3's both at 29psi when the tests were done.
Both cars were tested using the same speed and condition, with the GXP you feel more lateral movement as oppose to the 1st 1K.
The steering feels fine and so does the front, is just the back end.
I need to know since I do not think it has been posted what are the OEM alignment values for the GXP, is possible that the first few GXP's were miss aligned, remember mine was made before the factory shut down.
You all remember from the first day I drove the car my only complaint was the handling, then I upgraded the tires from the OEM to the 245/45/r18 GS-D3's and it improve some but never to the same level feel of the old car and the same tests.

[salstice]

I just wanted to add some food for thought. I believe that the Solstice (N/A or GXP) is a car that needs attention when uping the performance. I drive an N/A with the following:

CAI
Eibach Springs (1.4" rear, 1" front)
Vector ECM
Magnaflow Single Cat Back Exhaust
18X8 OZ Ultraleggera Wheels
Stock Tires (upgrading SOON!)
4-wheel alignment

Now when I had the car stock, it performed like it is was on rails. I could dip very deep into a turn and stick it. Now with all I have done, the car is very finicky in turns. I lose the rear end on command anytime I want to, and this is with an N/A with not nearly the amount of horse/torque that the GXP has. I am trouble shooting this by adjusting how I drive and replacing the stock rubber. I think those are the first, easy steps I can take. If that doesn't help me enough I think I will be tinkering a little more with the setup of the alignment to help keep my tail behind me.

[ender]

Wow... looks like your only real suspension change was springs. Makes me have second thoughts about ordering springs for my TurboSol. I'll wait for things to settle out a bit.

[SolsticeMan]

Originally Posted by Krazed Kanary Really? you used the electronic caster gauge to measure and set the front caster??? Where did you get the correct offset angle for the front from? ....

It's simple - look at the knuckles - the castings are the same. If you read the material in the service information, the offset you dial in (+3.7 degrees) isn't a secret at all. Just use the gage set to the "pass" side when you are checking the driver side front. It displays directly, but as a negative number.


And a hunter reads about a half degree low on average (an artifact from sweeping caster), and the particular machine I was looking at showed one side 3 tenths low, and the other side 9 tenths low. If you used the hunter readings to set the caster, you'd end up with over half degree cross.


If you mess up the rear caster (in cross) you WILL get obvious handling effects. I have personally experienced them. They are not pleasant.

[salstice]

Originally Posted by ender Wow... looks like your only real suspension change was springs. Makes me have second thoughts about ordering springs for my TurboSol. I'll wait for things to settle out a bit.

The springs have actually helped out a ton. It is the power increases and weight reduction that have given me the tail happy rear.

[ender]

Originally Posted by salstice The springs have actually helped out a ton. It is the power increases and weight reduction that have given me the tail happy rear.

How much weight reduction and how much power increase? So all this extra finickyness is because of the extra power to weight ratio?

I'd think that if that were the case, careful throttle modulation should allow the car to still handle like it was on rails... unless the alignment and springs screwed it up.

[Krazed Kanary]

Originally Posted by SolsticeMan It's simple - look at the knuckles - the castings are the same. If you read the material in the service information, the offset you dial in (+3.7 degrees) isn't a secret at all. Just use the gage set to the "pass" side when you are checking the driver side front. It displays directly, but as a negative number. And a hunter reads about a half degree low on average (an artifact from sweeping caster), and the particular machine I was looking at showed one side 3 tenths low, and the other side 9 tenths low. If you used the hunter readings to set the caster, you'd end up with over half degree cross. If you mess up the rear caster (in cross) you WILL get obvious handling effects. I have personally experienced them. They are not pleasant.

Quoting from the TSB:
TIP: If you study the front and rear suspension of the Solstice you may notice that the driver front knuckle resembles the passenger rear knuckle, and the passenger front and driver rear knuckles resemble each other. This suggests that you could use the gauge to check front caster. This would require inputting "driver" into the Digital Angle Gauge when working on the passenger side and vice versa. Don't be tempted to do this, however, because the front offset angle is different from the rear, and this specification has not been published.
end quote emphasis mine. I have measured the front offset, and it IS significantly (several degrees) different from the rear. You may want to recheck your front caster using the traditional method. If you set it as you indicated it is far more than 1/2 degree off you say your Hunter machine reads. (If it's that critical and you know your machine's error, why not just add it into your setting? Then check it with the gauge like you said, the readings will be wildly different.)

What are these unpleasant obvious handling effects and how were they measured?

Curious as to what type of racing are you doing with the Solstice?
Not trying to call you out here, but I'd just like to see correct info posted.

[SolAnderson]

dumb check
How about throwing some sandbags in the "trunk" to help neutralize the F/R weight distribution? If it's still handles worse than the NA then it must be susp component changes vs weight distribution problems. Right? Simplified I know, but hey process of elimination

[SolsticeMan]

Originally Posted by Krazed Kanary Quoting from the TSB: TIP: If you study the front and rear suspension of the Solstice you may notice that the driver front knuckle resembles the passenger rear knuckle, and the passenger front and driver rear knuckles resemble each other. This suggests that you could use the gauge to check front caster. This would require inputting "driver" into the Digital Angle Gauge when working on the passenger side and vice versa. Don't be tempted to do this, however, because the front offset angle is different from the rear, and this specification has not been published. end quote emphasis mine. I have measured the front offset, and it IS significantly (several degrees) different from the rear. ....

Exactly how did you measure the 'offset'?

Cause it sure ain't different on the parts I've seen. Set the ball joint holes to zero caster (straight up and down) and the gage holes make a 3.7 degree offset to the ball joint holes. Front and rear are the same, just different sign.

I do know that there is concern about the sign of the reading - and that for the gage to read the correct sign for the front, it would be necessary to build in another choice of front/rear, thereby increasing the cost of the gage (already more than a couple hundred $$), and the complexity of the method. In addition, I suppose some time in the future, maybe they might use different knuckles, or use another 'shelf' knuckle that doesn't have 3.7 degree offset. But then it would be obvious when the castings didn't have the same friggin casting number on them.

I must admit, I also have a ringer in the mix - I happen to know the company that makes some of the tools used in the assembly plant (the production assembly version of the field gage). Same offset, regardless of what the 'tip' says, and easily verified.

See, the 'offset' is not related to the position of the knuckle in the car, nor is it affected by gravity - it is the physical angle the holes make with the ball joint holes.

In the case I was talking about - the hunter swept at 7.21 left caster and 7.85 right caster. The caster gage read 8.1 (negative, but we know it will read negative, it's correct in magnitude) on the left and 8.3 on the right (sic).

Rears were both pretty much on -4.0 degrees.

Now, we did go forward and set caster with the hunter, at the specified 8 degrees both sides. BUT NOW the caster gages read 8.8-8.9 degrees on left, and 8.4 on right.

But NOW, the left caster adjuster was out of adjustment - it was as far as it would go (outboard, if you care). This didn't sit right in my head. I told the tech that if the car didn't feel right to me or the owner, we'd be back.

It took only about 15 minutes to figure out something was strange - I expected a drift, but instead found that the car felt... well, just weird. Like two different cars depending on whether you were turning left or right - and got worse if you pushed it in a corner. And when going over moderate bumps (of which there are PLENTY in the Ann Arbor area...) the steering would self-steer.

(and now the technician reading this prolly knows who I am... )

We went back, and re-did the measurements. After half an afternoon shot, NOW the hunter read 8.2 on left and 7.9 on right (remember, we left with them both dead-on 8.0 degrees), but the caster gage still read what it did when we left - at 8.9 left and 8.4 right. (AFTER going through the zeroing process, of course)

When we left that afternoon, the hunter sweep was somewhere in the low 7 degrees left, and mid-high 7 right, but the caster gage was dead-on at 8.0 both sides, and the owner was a happy camper. The car drove well, tracked like it was on rails.

Now, the owner may or may not be on the forum, but he also knows that the help I gave him should not be posted...


And I'll prolly never trust a hunter again, or at least treat the measurements with a grain of salt.


And if you saw the service group presentations I have seen, they spell out the handling effects of rear ride steer being different left to right.

[Krazed Kanary]

Originally Posted by fastmike If you are oversteering at the exit of the corner, you might be bouncing/riding on the bumpstops too much under acceleration or even in the middle of a corner. Rear toe can also have dramatic effect on the cars handling. At least tape measure check your rear toe. You should have at least a little bit of toe in. Use 2 people and check it. We found that both our ZOK's slipped to rear toe out after the first ever alignments. Don't know why. They seem to be holding now. Maybe a new car thing? FM

Mike, is the available travel that short that it can bounce off the bump stops? I haven't checked how much suspension travel we are using, might be an interesting thing to do at this weekend's event.
Good luck at the PS (I assume you are going?).

[birdliver]

Originally Posted by RobL Did your original car have the clutch diff? Going from a car that didn't have one to a car that does have one would explain everything that you describe (this is why the Elise originally did not come with a diff). FYI, the diff tries to keep the car pointed straight by making the rear tires move at the same rate. It feels different than an open diff that has no such restriction so the open diff allows more turning freedom.

Hi RobL,
My original car did NOT have the clutch diff. I think you have just solved this riddle. Since all the references to the clutch diff around here have been "do you have the LSD", I didn't think much beyond it's function when one wheel loses traction on a slippery surface. I wasn't considered the implications of what happens when powering through turns on pavement when one wheel wants to spin faster than the other. Thanks for the insightful post, it's great example of how helpful this place can be.-bird

[jimbo]

To be perfectly honest, I don't know what to think about the GXP's handling at this point...

We have very credible people reporting that the GXP just does not handle as well as the base car, wearing the same tires in the case of LV, and wearing better tires in the case of birdliver (GS2s over lousy RSAs).

We also have magazine reviews where the GXP achieved lower gs on a skidpad than were achieved for the base Solstice.

Being that I will be buying a GXP, the thought of it being inferior in handling to the base Solstice makes me a bit unhappy.

That said, I am only unhappy on paper, since I simply can't see driving my car at 9/10s or up on the street and I won't be taking it to a track. So I am saying, I'm unhappy that the GXP's bench racing handling character may be inferior to the base Solstice's bench racing handling character.

That said, what I am hearing is that the car "feels" like it handles worse than the base car. The question is, are your cars really inferior at handling and roadholding than the base Solstice? Do any of you really know.

My point goes back to when RODEO thought his MSM was a fast car because it "felt" like such a fast car. This is very important to the driver. You want the car that feels best, that feels like it handles the best. You can't discount that what you feel becomes your reality.

But when you guys say the car doesn't handle like your base car, are you saying that corner you took at a steady-state 70 mph in a stable 4-wheel drift in your base car is causing your rear tires to break loose as the car begins to spin? Are you saying that the limit of adhesion of your GXP occurs at lower speeds under identical conditions as your old base cars?

Are conditions identical? Did you get up to speed much faster on that short straight section in the quick GXP and have to hit the breaks a bit harder on entering that corner, unloading the rear end? That is the kind of thing that is possible. I know you will swear on a stack of bibles it is not like that. And both of you are very credible, and if you are really going into the same corners with the same entry speeds and the same braking force you did when you drove your base cars through those corners, then I absolutely believe the both of you.

But I still have to ask, if you didn't drive your base car to the limit of its adhesion and then drive the same corner to the limit of the GXP's adhesion and get different speeds when the car's tires exceed their limit of adhesion, then what does it mean to say that the GXP does not handle as well as the base car?

Again, this is all academic to me since I'm reasonably sure the car will handle way, way, way better than my pathetic ability to drive it.

And this is all academic to you because it really doesn't matter how well the GXP handles if it doesn't feel that it handles as well as the base car. Really, how it feels is all that matters to you. Feeling stable taking a corner at 70mph is more important to you than feeing like the car is loose at 70mph, even if your tire's reserve is actually equal in both cases.