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Old 02-02-2017, 02:02 AM   #1
CamaroDreams76
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Suspension help

I may be acquiring a set of Z/28 DSSV shocks and springs. I've read a few reviews of some 1LE guys running the entire Z/28 suspension kit. But I want to kind of run a lite version of this. I also want to put on AFE power / Pfadt sway bars (32mm hollow front and rear).

My car is a DD, and I've been getting into autox events. My current setup is the 1LE suspension, since I have a 1LE, pfadt solid subframe bushings, pfadt trailing arms and toelinks.

My main question is, how will this affect handling of my car? I want more cornering grip, predictability and to put power down sooner. I don't want to spend money if it will negatively affect the great job GM did with the 1LE but I feel like there is room for improvement for more grip and control.
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Old 02-02-2017, 05:47 AM   #2
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Springs, shocks and sway bars are all used for the purpose of controlling chassis motion (roll, squat, dive) which translates to chassis balance (oversteer and understeer) so considering the Z28 has similar size bars front and rear (25mm and 26mm I believe?) as well as a semi-square tire setup (like the 1LE, if you're using the factor setup), replacing your springs/shocks/bars with the ones you mentioned will make it handle more like a Z28.

Regarding predictability, since you're slowly converting to a Z28 you may want to look into Z28 (or aftermarket such as JPSS) radius rod bushing inserts - these will help inspire more confidence when cornering and braking hard by stiffening up/reducing the radius rod (trailing arm) movement.

Z28 rear upper control arm bushings will also help keep the rear wheels planted over bumps and when putting down lots o' power.

What are your alignment specs?
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Old 02-02-2017, 07:09 AM   #3
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Alignment is stock at the moment. I'd definitely would add some camber if I was running the setup I described.

AFE power says that the OE endlinks are used. Will this be putting more stress on them by stiffening up the sway bar?
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Old 02-02-2017, 09:15 AM   #4
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Factory links are adequate; there may be some added stress to the fasteners but not enough to risk component failure, and with your tighter springs there will be that much less roll and stress on the links. I have a 32mm solid rear bar (27mm solid front) and have not experienced any mechanical issues or even extra noise.

Regarding alignment, consider adding caster - caster provides easier steering wheel centering out of a turn (good for consecutive quick, tight turns) as well as adds more camber when the steering wheel is turned (so you can run less static camber and thus have better tire wear and stopping power).

To add caster, however, you must either grind out the radius rod bushing bolt hole (uses an eccentric bolt and guides but does not have an elongated hole for some reason, so you must elongate the hole yourself) or you can use camber/caster plates, although I'd recommend adding caster via the radius rod and instead save the camber plates (if you choose to get them) for camber - and thus steering axis inclination (SAI) - adjustment.

Increasing SAI helps with keeping your wheels pointed straight and will also bring the roll centre closer to the centre of gravity, reducing the amount that the front of the car will roll in the first place (before springs and bars come into play). If you add SAI you'll also want to add the extra caster as SAI will increase positive camber in turns.
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Old 02-02-2017, 10:49 PM   #5
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Thanks for all the info and input. Im not very familiar with suspension bits

Would love to hear more people chime in and drop their .02
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Old 02-03-2017, 09:54 PM   #6
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Quote:
Originally Posted by CamaroDreams76 View Post
Alignment is stock at the moment. I'd definitely would add some camber if I was running the setup I described.

AFE power says that the OE endlinks are used. Will this be putting more stress on them by stiffening up the sway bar?
Only add camber if it is needed. Too much camber decreases straight line braking, and stability this goes for both ends.
To establish where you are at you need a probe type pyrometer to measure the tire temperture splits. The measurements are performed off of a hot lap with 0 cooldown time. This may prove to be tough if only autocrossing, as the tires rarely reach optimum temperatures. It might be possible if they have hot lapping at the end of the day. Otherwise a track day is the only way your going to do this. It is a crucial step to sorting out any set up work needed, and identify short commings in balance and spring rates.

Luckily people like JPSS perform this kind of tire reading during development and understand what it means. Their advice will get you close. However reading your tires will allow you to fully dial it in to your driving style, and even the course, should you have some easy adjustability built in. I have often done non symetrical set ups taylored to certain tracks, depending on quanities of corners in certain directions. IE every corner of the car has different camber, and tire pressure settings. This is all done by reading the tempertures, and making adjustments for optimum contact patch.

I use it to evaluate alignment, and chassis balance, and would be happy to explain it in further detail if you would like to know more.
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Old 02-04-2017, 02:55 PM   #7
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If you are getting the Z28 springs/shocks, you are going to want the z28 swaybars. These shocks/springs are much, much, MUCH stiffer than the stock SS and 1LE setups. If you run giant swaybars with these, you will have way too much lateral stiffness.
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Old 02-04-2017, 09:45 PM   #8
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Quote:
Originally Posted by Nor Cal ZL1 View Post
Only add camber if it is needed. Too much camber decreases straight line braking, and stability this goes for both ends.
To establish where you are at you need a probe type pyrometer to measure the tire temperture splits. The measurements are performed off of a hot lap with 0 cooldown time. This may prove to be tough if only autocrossing, as the tires rarely reach optimum temperatures. It might be possible if they have hot lapping at the end of the day. Otherwise a track day is the only way your going to do this. It is a crucial step to sorting out any set up work needed, and identify short commings in balance and spring rates.

Luckily people like JPSS perform this kind of tire reading during development and understand what it means. Their advice will get you close. However reading your tires will allow you to fully dial it in to your driving style, and even the course, should you have some easy adjustability built in. I have often done non symetrical set ups taylored to certain tracks, depending on quanities of corners in certain directions. IE every corner of the car has different camber, and tire pressure settings. This is all done by reading the tempertures, and making adjustments for optimum contact patch.

I use it to evaluate alignment, and chassis balance, and would be happy to explain it in further detail if you would like to know more.
Makes sense. I appreciate the help.
Quote:
Originally Posted by derieu View Post
If you are getting the Z28 springs/shocks, you are going to want the z28 swaybars. These shocks/springs are much, much, MUCH stiffer than the stock SS and 1LE setups. If you run giant swaybars with these, you will have way too much lateral stiffness.
Kinda what I was thinking since the Z/28 runs smaller bars than the 1LE.
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Old 02-04-2017, 10:08 PM   #9
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Are the factory Z28 bars solid? If so a 25 or 26mm solid bar may not be much weaker (for lack of a better term) than a 32mm hollow bar - depending on how thick the hollow bar is, of course. The 32mm bars in question might be stiffer, but if so then not significantly. Here is a link to what I'm referring to: https://forums.nasioc.com/forums/sho...d.php?t=910253. Read this many a months ago before I installed my bars. Try putting the numbers into the equation and see what you get - the factory bars may even be stronger.

Last edited by KillboyPowerhead; 02-04-2017 at 10:16 PM. Reason: Re-worded...
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Old 02-05-2017, 05:25 PM   #10
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So I did another AutoX event. It had some pretty technical sections and I didn't do too well on a few runs. My 1LE turned into an expensive snowplow (understeered like crazy) cone killer. Will this Z/28 stuff change this? I realize, when you have too much speed it's inevitable.
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Old 02-05-2017, 05:47 PM   #11
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To correct understeer you can firm up the rear end. A bigger rear bar would help, and I wouldn't use those bars you mentioned as they're hollow (i.e. not much stiffer then your existing ones, if they even are), but rather a solid, 32mm bar (JPSS has one) - this will give you a 5mm difference between the front and rear bars which JusticePete claims to be the sweet spot with a square tire setup.

Alignment specs?
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Old 02-05-2017, 06:53 PM   #12
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Stock 1LE alignment.

Hollow bars can be stronger than solid bars. Supposedly multiple Porsches and performance cars run hollow bars to decrease weight. It really depends on the thickness they use. BMR states they use .188
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Old 02-06-2017, 10:39 AM   #13
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They for sure can be, but are they? Do you know how thick the bars are? 0.188" or is that BMR and not Pfadt? I'm just saying, a solid bar will be stiffer than a hollow (of equal diameter), and if you want less understeer and you have a solid 27mm bar up front, you may need a solid 32mm bar (or so) in the rear - a 32mm hollow bar may be stiffer than a factory 28mm bar but likely not as stiff as you need to correct this "crazy" understeer (of course, that depends on how thick the bar is).

A hollow bar will be lighter but it will also be bigger to meet the required stiffness; if you want less understeer a 32mm hollow may not be enough with a 27mm solid front bar, but you'll need to know the thickness of the hollow bar in question to know. The equation seems fairly straight-forward; easy enough to find out.
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Old 02-06-2017, 06:12 PM   #14
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Please supply tire manufacturer, tread wear rating, and a picture of the front tire sidewall, and contact area.

Also when is the understeer occuring, off throttle, on throttle, corner entry, corner mid, corner exit. Each one of these situations has a specific cause and correction, and is not always fixed until you know the correct part or adjustment, also need to know if the supsension is loaded, or unloaded.

Also as I said before getting the temp is curcial to set up, so to get that data. It will reveal almost everything that is wrong, or right with your balance, alignment, tire pressure, spring rates. Once you establish the contact patch is utilized fully and the temp spreads are good that will verify alingment, inability to get the spread correct verifies, spring rate, body roll issues for the given course.

Alot of people go and just worry about tire pressure, when in the racing world it is used to set mid tire temp only. I will give you a few examples using the driver front tire only, with right hand turns only. The correct spread your shooting for is 10 to maybe 15 max. The tire should always bet warmest on the inside and gradually cooler towards the outside.

Examle 1

Outer 140/Middle 135,/ Inner 130..... really really bad camber, tire pressure ok
Causes alignment, too soft spring, too soft sway bar. Start with alignment, adding negative camber.

Example 2

Outer 130/ middle 135/ inner 140..... perfect on the money camber ok.... pressure ok

Examle 3

Outer 128/ middle 138/ inner 140..... tire pressure too high utilizing too much inner and mid. Reduce pressure and check again
Possible excessive negative camber


Example.4

Outer 135/mid 124/inner/ 141. Tire pressure too low increase and check again.


Example 6

Outer 175/mid160/inner 150.... super bad camber, but most likely a very soft spring rate rolling onto the outer edge.

Now when you look at all 4 tires they all tell a story and how things are working esp side to side and front to back.

A poorly balanced car front to back will usually have hotter tires on the end, or even corner that is sprung to softly. But in this case you also have to note where the car has push, or loose in the corner as each of these has different causes relating to differential lock/coast, rebound and compression dampening etc. A car pushing on exit under throttle is unloading the front, and transfering to rear. The understeer causes could be too soft rear springs, too low rear compression, too much diff lock, too slow front rebound ect. Being able to read the tires and decipher will point in the correction to be made for given issue.


Also be wary of those online guides as the can be a bit misleading.
An example of this we have a drivers front tire, a bunch of right hand turns. The tire makes optimum grip at 175 degrees core. The car has understeer, and the tires have gone off, or turned greasy. Here are the measurements.

Outer 250/ mid 255/inner 260. Ok the spread is good, pressure is good, but the tire is waaaay overheated. Well the driver could have been over driving the tires, or the set up is incorrect. Most guides will say, soften the front for more weight transfer to lessen understeer. In this case the tire has already been overloaded and adding weight transfer to it is going to make the temperture even worse. It seems opposite, but in this case the car has begun to understeer simply because the tires can't support the load from the transfer to begin with. They then overheated and the understeer became worse as the traction levels went off. The cure in this situation is the opposite, the front needs to be stiffer to slow the rate of transfer to front tires to keep them closer to their operting range. Not knowing the tire temperatues this kind of problem solving is purely guess work.



My bet is there is a lot still on the table with the parts you have already

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