Hollow or Solid Sway Bars?

I have a 2001 Z28 that I want to set up for roadracing. I was wondering what would be better, solid or hollow sway bars? and should I keep the stock rear or buy a 21mm?

hollow sway bars have almost the exact same anti-sway abilities as a solid bar with an identical diamter...

anti-sway bars are for tuning the suspension... 21MM rear bar might be great for one track, and a 19MM bar might be better for a different track



[This message has been edited by prockbp (edited June 10, 2002).]

i've heard that the difference between solid and hollow is that solid equals about 2 more mm dia. in hollow...in ohter words...

32mm hollow equates to 30 solid...

my BMR 32/21mm solids are great...love them.

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ARREST-ME RED 96 Z-28, M6 (http://www.gmmuscle.cz28.com/images/jeff.jpg)...stock for now...but i've only had it three days...1st mod on day 4! TB airfoil...NOW...G2 CAI(modified), K&N, MagnaFlow w/ cutout(closed of course), maf ends, ?cags?, UD pulley, TB bypass, 160stat, SLP fan switch (http://www.slponline.com/view_product.asp?PARTNUMBER=63011), SLP air temp module (http://www.slponline.com/view_product.asp?PARTNUMBER=63010), Hypertech PTM, MSD 6A, Hurst(SS donation) with a Lou's SStick (http://lscamaross.8m.com/lous2.html) and Proform Shiftlight (http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=39231&prmenbr=76), BMR (http://www.bmrfabrication.com) lca, phb and stb, 32/21mm sway bars w/ poly bushings and endlinks, ES poly TA mount, air silencer???

Waiting to go on: 1LE springs, SLP afpr

For Sale: stock exhaust+ sq. tips, 30/19mm sway bars w/ stock bushings

I don't know but the metal it's made from would certainly have some significant effect too. A softer metal on a solid bar may not be as good as a stiffer metal. Anyone know as I am curious also.

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95 Z28, SLP Y pipe, Flowmaster muffler, SFC, STB, KYB shocks, Moroso CAI, 1LE front anti roll bar, Hurst shifter, TBB, LT4 KM, LG Motorsports pedals

<font face="Verdana, Arial" size="2">Originally posted by warner:
I don't know but the metal it's made from would certainly have some significant effect too. A softer metal on a solid bar may not be as good as a stiffer metal. Anyone know as I am curious also.

</font>

There's little difference in the inherent stiffness properties among the various grades of steel. The modulus of elasticity generally falls within about a 10% range (26E6 psi - 30E6 psi). And I'm not aware of any bars made from aluminum (10E6 psi)

[Edit, see the following post for the correct formula. NoveScotiaRS caught me with my brain in neutral]

Since it's a 4th power ratio, small changes in the diameter ratio show up as much larger changes in the stiffness ratio, so measure carefully.

Norm

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1979 Malibu, 355, 5 speed, cornering tweaks, some other stuff
2001 20th Anniversary Maxima, 5 speed

[This message has been edited by Norm Peterson (edited June 17, 2002).]

You are one the right track, but have made an error. The formula for torsional stiffness of a torsion bar is:
K = JG/L where:
K is the stiffness of the bar,
J is polar moment of the cross section of the bar
G is the shear modulus of the matrial, and
L is the length of the bar.

Given that all sway bars for the 4th gen camaro are the same length, the arms of the sway bars are the same length, and that steel is steel, then comparing stiffness is a matter of comparing J.

for a solid bar: J = pi * OD^4 / 32
for a hollow bar: J = pi * (OD^4 - ID^4) / 32

the formula for compairing bars is:
J1/J2 or
(OD1^4 - ID1^4)/(OD2^4 - ID2^4)
and ID = 0 for a solid bar.
(Not OD^4/ID^4)

So a solid 19mm bar compaired to a 21mm-10mm hollow bar is 19^4 /(21^4 - 10^4) which works out to 0.70 or 70%. A 19mm solid bar has 70% of ths stiffness of a 21mm bar with a 10mm hole in it.

Likewise a 21mm bar with a 15.9mm hole through it is the same stiffness as a 19mm solid bar.

&lt;edit&gt;
The advantage of a hollow bar is that a hollow bar is lighter than the same stiffness solid bar. Looking at the 19mm vs the 21mm-15.9mm above:
the hollow bar weighs: L*pi*(21^2-15.9^2)*density/4
the solid bar weighs: L*pi*(19^2)*density/4
So compairing the mass of these two:
(21^2-15.9^2)/(19^2) = 0.52 or 52%

The hollow bar is near halve the weight of the solid bar and is as stiff!!!
&lt;end edit&gt;

Regards,
Derek

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[This message has been edited by NovaScotiaRS (edited June 12, 2002).]

Ouch ... that hurt my brain.

So, which is better ...

35mm (ST) solid or 32mm (1LE) hollow?

Go for the 35mm ST bar, without running the numbers I can subjectively say that your car will be noticeably stiffer in roll with the 35mm solid. Not to mention Strano seems to like them. Once the front bar is out of the way its a matter of balancing it out at the rear.

I've got the 35 ST on the front now and a 21mm 1LE on the rear.

I picked up a significant push ...

Maybe the 25 ST rear bar?

My car is fairly neutral with the ST 35/25 combo and stock shocks and springs.

After adding the Nitto DRs, it pushs a little longer on exit, but more throttle fixes that. http://web.camaross.com/bb/smile.gif

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Solomon
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