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Old 03-21-2009, 02:23 PM   #1 (permalink)
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Lowering GXP for better handling?

Will lowering the GXP help its handling? I use to have a mx5 and miss the handling and cornering
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Old 03-22-2009, 02:06 AM   #2 (permalink)
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Check out the ZOK Club Sport "FE3" suspension...

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Originally Posted by spacie View Post
Will lowering the GXP help its handling? I use to have a mx5 and miss the handling and cornering
Hi spaice,

Welcome to the forum!

Lowering alone is not enough. If you really want to get a bit flatter cornering, faster turn-in, and taught handling, you'll need to sacrifice a bit of comfort, and have to be prepared to have the ride be a bit bumpy over ordinary road surfaces.

The race track by comparison is usually (though not always ) VERY smooth. Thus, suspensions that are correct for the track can be a bit grating on the nerves in daily driving over the relatively rough public roads.

If you're really serious about this, typically, you'll want a balanced package which includes ALL of the following which have been tuned so that their spring rates, damping (both compression and rebound) are tuned to keep the tires on the road:
  • Front and rear sway bars
  • Sway bar mounts & bushings
  • Dampers
  • Springs

In point of fact, sometimes lowering a car can make it's roll center move below it's center of mass, and that can lead to very odd dynamic behavior. So, again, you're looking for a balanced approach, and installing springs to lower the car by themselves may not get you what you're looking for.

If you're lowering for aesthetics or appearance, then just a set of springs is all you need, but if it's handling, you should choose more carefully.

There are lots of kits available to do this. Indeed, several of the vendors on this site offer spring kits, and even whole kits that will offer much of what you're looking for.

One thing to keep in mind is that the spring rates and damping rates for compression and rebound are fairly well tuned in the stock suspension, so while it may feel a bit looser than you might be used to, it's actually gripping the road very well. Don't make the mistake in assuming that just because the car's suspension will actually deflect when you go over a rough surface, that the suspension must therefor be too "soft".

There was also the suspension from the ZOK club sport package, "FE3 suspension". It was specifically designed for track use. It was mentioned here: GM 2006 SEMA.

I'm willing to bet that our very own Small Dealer knows all about the GM packages available....

How about it, Small Dealer? What's Pontiac/GM got for the enthusiast who doesn't mind the ride being a bit bumpy?

Again, opinions will vary wildly, and you'll get all kinds of answers. But you might want to check out the ZOK "FE3" suspension. The chassis engineers that designed the package did a superb job.

Again, welcome to the forum.
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Old 03-22-2009, 09:29 AM   #3 (permalink)
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All of the above is spot on EXCEPT that the GMPP handling package offered in 2006 was basically the FE3 suspension (VERY close) that was standard on the upcoming GXP and Redline. As time has passed lots of (the above mentioned) choices surfaced. The newest ones are the DDM developed ProBeam (rear frame/suspension) brace and BackBone (body stiffener) which substantially improve the rigidity of the platform. A stiffer platform allows the existing suspension to work better as the body isn't twisting and flexing as much (and it DOES). QUICKEST/CHEAPEST would be sway bars and the Z0K bars from Pontiac for the GXP (NOT the Z0K bars form the 2.4). Next, the GXP Z0K springs will lower the car 1-1.3" and are about 20% stiffer. If you want a bit more refined ride and handing then after market shocks can be had from under $600 (Koni SA) up to wallet busting models (Penske and Ohlin). Use the SEARCH function and you'll find LOTS of threads to study up on.
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Old 03-22-2009, 10:04 AM   #4 (permalink)
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I prefer to keep it simple. A completely engineered aftermarket suspension system matching aftermarket spring rates, (etc.) is good for national level racing, but it really isn't needed for DD's.

As for your question, I don't find it very specific. What do you miss? The GXP handles quite well IMO. What do you want to improve?

IME from doing AX to see the GXP at its limit (and beyond it), the tires are very budget minded and not very high performance. Upgrade the tires. The car pushes far too much. So less front sway bar is better in this case, and some people have downgraded the swaybar in the GXP to the 2.4 base version. This is supposedly a nice improvement. And finally a coilover set up should improve the handling (at the expense of ride comfort over rough roads). I bought KW V3's which offer superior adjustability to any off the shelf coilovers out there right now. Independently adjustable compression and rebound damping. To improve the front end push (without doing any swaybar change yet) I have softened the compression up at the rear (and run a few less pounds in the rear tire during autocross) to get the rear of the car to rotate easier.

Add it some additional bracing as mentioned earlier and you would have a nice platform to work with.
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Old 03-22-2009, 02:08 PM   #5 (permalink)
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I put an FE2 bar on the front of my Redline and immediately lost over a second at local events. The car leaned like a 2.4. The hot lick of the GXP/Z0Ks seemed to be a Z0K read bar with an FE3 front bar. Same theory, but done with INCREASED roll resistance overall, not less. And roll bars do nothing to "stiffen" the ride except in hard turns - sort of. A stiffer rear bar WILL make the car more neutral.
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Old 03-22-2009, 02:08 PM   #6 (permalink)
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All good info here.

If you decide to go with coilovers you need to balance your spring rates with your swaybars. Stiffer spring rates make up for smaller sways and vice versa.

You just need to decide what makes more sense for your car and how you drive it. All the suggestions named here have pros and cons.

We carry a lot of suspension items for the Solstice. Feel free to PM me with questions
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Old 03-23-2009, 08:43 AM   #7 (permalink)
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Quote:
Next, the GXP Z0K springs will lower the car 1-1.3" and are about 20% stiffer.
The GXP ZOK springs lower the car 1.75". The Eibach Pro-kits lower 1" in front and 1.3" in the rear.
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Old 03-24-2009, 08:38 PM   #8 (permalink)
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So will I ever get close to the " feeling" preformance I had in my 2002 MX-5 six speed?
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Old 03-25-2009, 03:18 AM   #9 (permalink)
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That depends... Can you articulate what you were "feeling"?

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Originally Posted by spacie View Post
So will I ever get close to the " feeling" preformance I had in my 2002 MX-5 six speed?
The biggest part of achieving a "feeling" of performance is to define in words what that feeling is.

Now, others have brought up an excellent point. If you're after really high lateral G forces, you can easily switch the tires for some high grip tires like the Michelin PS2's, the Goodyear F1 GS-D3's, or even go all the way to DOT legal race tires like the Michelin Pilot Sport Cup. (I don't really recommend going all the way to race tires, but the other two are good choices.)

You'll also feel a bit faster turn-in with a stiffer tire, like an XL (extended Load) or also with run-flat tires. The sidewalls tend to be stiffer, and flex less when you transition from straight line to turns, making their transition to lateral force more immediately felt. So perhaps, a new set of rubber is in order. It's actually the largest improvement you can make, and it doesn't require tearing the suspension apart. You'll notice much higher upper cornering limits, and you'll start to think that the sway bars, stiff springs, and stiffer dampers from the ZOK package might be a good investment.

However, if you stay with the stock tires, the suspension changes you make will be far less noticeable.

Again, the danger is that with a higher grip tire, you might wind up developing some very bad habits of using sharp or abrupt inputs on the gas, steering, or brakes. You'll do this because at 80% of the tires grip, the tires have ample capacity to give you all that cornering, braking, and accelerating. However, when you're out closer to the limits, such radical moves will put you in the guard rail. Also, the PS2's will not make very much noise at all when you lock them up, and stabbing the brakes will lock them up. When locked up, PS2's will slide and make only as much noise as a deck of playing cards dragging over a table. Smoke will be pouring out, but you won't hear much. Thus, they are VERY easy to flat-spot if you stab the brakes, and that's an expensive mistake to make, especially at $300 per tire.

If it's a stiff, taught suspension you want, the ZOK package may be just the thing to feed your kids!

The truth is that the Solstice in Showroom Stock B is handing the Miatas of your vintage their hats. So much so that the SCCA had a petition this year to help out the Miata. (The petition was denied. I would speculate in part because the Miata had dominated the SSB class for more than a decade, and the amount that the Solstices were beating the Miatas by was not "running away with the race", but some good old fashioned competitive racing.)

By the way, I use the SSB class specifically because it requires stock suspension.

If you're after the "twitchy like a bumble bee with a saddle" ride, you might not get it. Part of the reason why is that with the high belt line (tall doors--they come up to pretty much shoulder height) you will feel planted in the seat even at 0.85 Gs, where in the low door Miata, where the door's closer to your elbow, you might feel like you were more likely to fall out due to the cornering force.

Another part of the reason that the Solstice seems much more planted than the Miata is that it is very close to critically damped.... What's that? It means that it almost doesn't bounce up at all when you go over a bump. What it really means is that the damping allows a rapid return to neutral with just enough damping so that there is only the return stroke, and not any oscillating around the neutral point, but also that the return to neutral is as rapid as possible without any movement past neutral.

The Solstice is also not over damped, which would make it jitter across the road with small imperfections, because the rate of return to neutral (and the ability to keep the wheel on the ground as it rises and falls relative to the body) is too slow, so the tires actually leave the ground while the shocks keep the springs from pushing them back down (in the case of rebound), or that the shocks act like steel bars and resist the upward movement of the suspension so much that the motion is translated to excessive upward motion of the body (in the case of compression). Thus, when the body is launched upward by the small bump, and the tire doesn't come back to the pavement quickly, there's a period of time where there's no traction (or reduced traction) The result is that the car will literally step abruptly sideways during a turn when you go over a bump. If the bump is severe enough, you'll wind up off the paved surface.

The critical damping takes each jolt, complies with it (the suspension soaks up a lot of it) and the wheel / tires keep in contact with the ground far better than either an over damped or under damped car. The net result is a VERY planted feel. Bumps are bumps, and you don't bounce all over the place, nor do you skitter off to the side.

Because there's a fair amount of roll stiffness as well, the car is VERY quick to "take a set" when you make a steering input--you turn the wheel, the car squats just a little, rolling slightly to one side, settles immediately, then turns in the direction you pointed it. There's really not much drama.

A lot of folks associate the drama of an under damped car with "it must be going fast!! IT'S ALL OVER THE PLACE!!" Others associate an over damped car with high performance--it's rock solid, and when it goes over a bump, it just jumps sideways, but never bounces.

In the first case, the under damped car can be made to oscillate and bounce all around with radical inputs and surface imperfections. In the case of the over damped car, it just skitters off the road due to imperfections in the road surface--not bouncing a bit as it winds up in the ditch. Needless to say, both of these are not the fastest way around the track. The car with critical damping will always triumph.

So, now that I've waxed lyrical about this for way more than long enough....

What exactly are you looking for in the handling?
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Last edited by Crimson Avenger; 03-25-2009 at 03:30 AM.
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Old 03-25-2009, 06:11 AM   #10 (permalink)
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I would not suggest getting run flats if you are looking for a good handeling tire. because of the thicker/stiffer sidewall they also weigh quite a bit more than a standard tire.
if you are looking at tires I would also look at the Bridgestone RE01R or the RE11.
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Old 03-25-2009, 07:50 AM   #11 (permalink)
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Quote:
Originally Posted by Crimson Avenger View Post
If it's a stiff, taught suspension you want, the ZOK package may be just the thing to feed your kids!

The truth is that the Solstice in Showroom Stock B is handing the Miatas of your vintage their hats. So much so that the SCCA had a petition this year to help out the Miata. (The petition was denied. I would speculate in part because the Miata had dominated the SSB class for more than a decade, and the amount that the Solstices were beating the Miatas by was not "running away with the race", but some good old fashioned competitive racing.)

By the way, I use the SSB class specifically because it requires stock suspension.
I believe you will find that the winning SSB Solstices are Z0K versions while the Miatas are stock. The 2007s (or 08s, I can't remember which) were momentarily allowed to run their "port installed" Club Sport package in SSB but SCCA reversed itself. (Oddly the trunk package was deemed legal in C/Stock and still is, but only the one model year. Without the Z0K package the 2.4 Solstice would be a backmarker. The stock late model Miata is, in stock forum, too high and soft with no LSD and weak sway bars while the 2.4 Z0K has stiffer springs and bars WITH LSD and ABS.

BTW, I have no love for the Miata at all.
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Old 03-25-2009, 08:26 AM   #12 (permalink)
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Quote:
Originally Posted by mena661 View Post
The GXP ZOK springs lower the car 1.75". The Eibach Pro-kits lower 1" in front and 1.3" in the rear.
I already have a GXP and wanted to lower it for a better look and I saw from other threads people posted saying the Z0K springs are like .75" to lower but your saying there 1.75". Is there any confirmation on how much they actually lower? Since the Eibach one's lower 1.3 all around I wanted something a bit less than 1.3 since I already scrape on some driveways around here in socal.
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Old 03-25-2009, 08:28 AM   #13 (permalink)
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What would be the effect of lowering the car by keeping the stock GXP suspension but going with a shorter tire, say 225/40 on an 18 X 7 1/2" rim? There'd be a bit more space in the wheel wells above the tires, maybe noticeable; but the car would be lowered about 3/4 of an inch.
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Old 03-25-2009, 08:55 AM   #14 (permalink)
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Originally Posted by Filipp View Post
I already have a GXP and wanted to lower it for a better look and I saw from other threads people posted saying the Z0K springs are like .75" to lower but your saying there 1.75". Is there any confirmation on how much they actually lower? Since the Eibach one's lower 1.3 all around I wanted something a bit less than 1.3 since I already scrape on some driveways around here in socal.
There's a pic on the forum with a member that installed ZOK springs on his car. The front airdam is damn near dragging on the ground. I think some people are confusing ZOK with GMPP as the GMPP springs lower the car only 3/4". The ZOK's are MUCH lower. Do a search in this part of the forum. The info is here.

EDIT: Found it HERE.
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Old 03-25-2009, 10:14 AM   #15 (permalink)
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Quote:
Originally Posted by mena661 View Post
There's a pic on the forum with a member that installed ZOK springs on his car. The front airdam is damn near dragging on the ground. I think some people are confusing ZOK with GMPP as the GMPP springs lower the car only 3/4". The ZOK's are MUCH lower. Do a search in this part of the forum. The info is here.

EDIT: Found it HERE.
Ah I see, I think that is where me / others might have been confused with. Do you recommend going with the GMPP springs for my GXP if I wanted to lower it a bit but not to much? I just think 1.3" from the Eibach's might be a bit much, I don't wanna have to do uturns to avoid speedbumps / steep driveways.
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