365ZUM

Hey guys,

Ive decided to buy sway bar(s) for my vette and am trying to decide what size to get. Ive read alot of the previous posts on the subject, and alot of you recommend the 30mm solid up front, with a 26mm solid in the rear. Only thing is, I plan to change to 275/315 tires in a few weeks. Noticed on the suspension chart (www.vettenet.org/susp_chart.html) that ALL ZR-1's which have 275/315 tires (of course) use 26mm tubular's up front with 26mm solids in the rear. Why would GM use the 26/26 set-up if the 30/26 is better??

I drive my car everyday here in Charleston, and the roads are terrible. Every time I hit a bump while cornering at a significant speed, my car goes all over the road!! :mad I want to put a stop to this with a VERY aggressive anti-roll bar setup. Which should I purchase? :confused:

bogus

ok... heres how all this adds up...

if you have the same size tire all the way around...

A larger front sway bar will induce understeer.

a larger rear bar, in turn, will cause oversteer.

now, if you add larger rear tires, you will add to understeer.

if you then add a stiffer front bar, along with the bigger rear tires. all hell breaks loose and you are unable to make a turn to save your life!!!

now, factory tuning will lean towards understeer. this way you don't kill yourself in a corner, and your estate sues the maker...

if it was mine, I would go this way -

the big rears, 26mm hollow up front and a 30mm solid out back.

I would also consider installing coil overs, thats my plan at least.

trrgod

Bogus' suggestions sound bogus to me. I've never heard of anyone suggesting this particular set up?

365ZUM

hmmm...ttt

bogus

just because it has never been done does'nt mean it is wrong...

the reasoning is simple - the bigger rear tires lead to understeer, putting a stiffer rear bar will reduce understeer, and the goal is a touch of under with leanings towards neutral. thats the best setup for the street, from my estimations...

chassis setup is one thing I have quite a bit of expierence with... 15+ years of racing Radio Controlled cars (oval, touring and offroad) you get to know what does what... the last 6 years or so at that great semi-pro level - you know - spending money like a pro, but still not going any faster?

the funny thing, what works on a RC car chassis works on a real car chassis. Of course, the numbers are far different... the transverse leaf springs on corvettes range from 625lb/in on down... we were being wacky using 25lb (I never did find out if that was inches or what) springs with 40wt oil in the shocks!!! yes - RC cars use oil filled shocks...

HiRiser

word of warning, big bars will make your car hit the bumps really HARD on crappy roads.

silver & red CE

Bogus has it right until he calls foir the bar sizes. I've never seen a rear bar stiffer than 26mm solid. 26mm hollow in the front with 30mm solid in the rear is going to have wicked oversteer, no matter what size tire in the rear.

Here's my thoughts:

With 275s all around, the most neutral set up is the 30mm solid front, 26mm solid rear. Since the 315's in the rear will give the car more understeer, you might want want to make the front bar a little less stiff by dropping the size to 28/26mm solid (if they are available).

I'd go for the 30mm solid in the front, 26mm solid in ther rear, see how it handles. If it's pushing too much, look for a smaller front bar.

I've driven my Vette 5K miles with the 30/26mm solid combo and I love it. The roads here aren't the best and IMHO, the change in handling was worth a very slight increase in NVH.

Eric

bogus

the bar sizes you recommend do make more sence than the 30mm rear bar... I admit, that is a big bar, but not too big to be usefull...

No Go

Well I have no engineering support, but...

I elected to add 30 solid front/26 solid rear to my base suspension 96 to which I also installed set of 9.5/11 with 275/315 Pilots.

I mainly did it cause it only cost 155 bucks or so for both bars from Chevy and really firmed the ride and seemed to make the car much more controllable.

The understeer/oversteer issue is one that I can't say I fully understand on the track as during autocross I'm able to get understeer when I want it and oversteer when I want it. On a roadcourse I can put the car in four wheel slides on most corners, again getting either handling movement depending on how I come into the corners.

In other words, for a beginner/nonexperienced fella the combination works awesome for the cash outlay. The car is way over my head as far as capabilities-I need a driving course before I need to modify the suspension again...:)

By the way, part numbers are on my Homepage...Good Luck!

JasonL

My opinion...if you're worried about understeer with the 30/26mm combo, put all rubber bushings on the front 30mm bar. Use poly on the rear bar only. It won't make a gigantic difference, but it will help a little bit.

I know a few C4 racers who feel the 30mm front is plenty big, and sometimes even try to soften it up a bit.

MarkBychowski

Before I bought my current wheels, I had 275/315s with 30mm solid front and 26mm solid rear. Poly bushings on both bars. Stock soft '96 shocks and springs.
On the track it actually worked very well. It did have a little understeer, which is preferable to oversteer anyway.
As mentioned above, though; just about anything you do to stiffen the car up will cause it to get squirrly when hitting a bump in a turn. In my humble opinion, new bars won't help that problem -- they may hurt. Revalving your shocks may be your best bet there.
Hopefullyt HRocks will reply -- he's got much more suspension experience than most of us.

92TripleBlack

Here's what they all had. http://vettenet.org/susp_chart.html
Notice the GS with your tire sizes had 26 tubular front and 26 solid rear. My 92 convertable has 26 tubular front and 22 solid rear. I want to increase the rear to a 26 solid. Right now though it handles very well with the large tires and stock setup.
Hope this helps
92TripleBlack :cheers:

bogus

I still think the best solution to any handling problems the C4 has is the coilover kit...

I really want the full suspension kit from DRM... poly bushings, the brakets for anti-squat and camber adjustments and the aforementioned coil-overs.

From what I've read, the set up is just increadable.

92TripleBlack

Rippie's setup looks good. Vette Brake Products is supposed to have a good one also. I'd check them both out. Remember to keep it in context of how you want to use it. I drive through pothole central every day. The Japanese even came here to make plaster casts of the potholes so they could recreate them for testing. I would love a 1G+ car but only if I lived south of the snow line. As it is, I definitely pull over .9 with the better larger size and the better rubber. (This was definitely a major improvement over the GY and even the Bridgestone though not as pronounced.)
92TripleBlack :cheers:

bogus

the idea behind the coil over makes all sorts of sence to me... the transverse spring is capable of creating a torsen bar effect... this is bad.

There is also the resonance factor that causes the factory setup to quiver and shimmy.

I suspect that under most conditions, the coil over systems will do nothing but improve the car overall... ride, handling, you name it.

GRX

Bogus is correct about stiffer bar at the front inducing understeer and a stiffer bar at the rear inducing oversteer. That's as basic as it gets. :smash:

NASCAR314

Does anybody know the GM-Part numbers for the 30mm front and 26mm rear (both solid) used I belive on 1991 Z07 equipped models???

I'm just looking for the part #'s

Thanks,

importeater

great example of a street car is the z06, you use a sticky tire. stiff chassis but modest suspension and 1g is possible. one of my good friends has a z06 and it's not at all a rough car yet stays pretty flat in a corner and pulls hard. i think on my own car i'm just going to urathane the bushings. use the bilstein sports shocks i have & find some nice tires...works for me

John Row

As I recall my Navy basic engineering, a hollow tube is stiffer and can take more torque than a solid bar of the same diameter. I don't know the equations, but the 26mm tube may end up acting like a 30mm bar, plus it will be lighter.

Just a thought,

silver & red CE

This isn't correct. For a given diameter, a solid bar is aways stiffer than a hollow bar. A 30mm solid bar will be ~2X as stiff as a a 26mm solid. A 26mm solid bar will be ~1.5x stiffer than a 26mm hollow (assuming 6mm wall thickness) and a 30mm solid bar is almost 4X stiffer than a 26mm hollow.

from: Swaybar Design by Scott Mueller
http://www.b-body.net/Technical/Susp...s/swaybar.html

BAR THICKNESS - As has been noted the stiffness of a bar is proportional to the 4th power of the diameter. A bar that is twice as thick as another will be 16 times stiffer! This means that small differences in thickness make large differences in rate. This calculation can also take into account whether the bar is solid or hollow, by subtracting the rate from a bar matching the ID or hollow space within.

The stock front bar is 30mm in diameter, and is solid. We know that the Herb Adams (HA) front bar is 1-5/16" (1.3125") in diameter and is solid. We know that the John Hotchkis (JH) front bar is 1-7/16" (1.4375") in diameter and is hollow, with 0.25" tube wall thickness. This gives an Inner Diameter (ID) of (1.4375 - 0.25*2) or 0.9375". Based on thickness alone, we can therefore calculate the relative rate (stiffness) of the front bars as follows: OD^4-ID^4 = Relative Rate.

OD ID Relative Rate % over Stock
Stock 1.181 0.0 1.946 0.0%
JH 1.4375 0.9375 3.498 79.7%
HA 1.3125 0.0 2.968 52.5%
F-car 1.2500 0.0 2.441 25.5%

This shows that the larger, hollow tube JH bar is nearly 80% stiffer than the stock bar, while the HA bar seems to be only 53% stiffer than the stock bar, that is if we take only the diameter of the bar into account. However, as has been said somewhere before, "size isn't everything", as we soon shall see!

BAR LENGTH - The stiffness or rate of a swaybar is inversely proportional to it's length. Given two bars of the same diameter and other specifications, one that is twice as long will have half the rate or stiffness. For the front bars, they all have relatively the same length, which is dictated by the width of the vehicle frame at that point. All of
the front bars are about 35" wide between the pivot points. Therefore no adjustment in the relative rate calculations are necessary between the different bars.

SWING ARM (LEVER) LENGTH - A swaybar is a torsion bar, and force is applied to the bar via a lever on each end. The length of this lever is very important! The rate of the bar is inversely proportional to the length of the lever you use to exert force on it. This means that given two bars with identical properties, if you make the lever arms on the end of one twice as long as the other, you will also cut the relative rate (stiffness) in half.

Eric