Sway Bars - Hollow or Solid

[KozanBMW]

Which is stronger and why?

Thanks,
Steve

[RRSperry]

Given reasonable wall thickness, hollow is stronger. It's an engineering thing...

Which means, I'm too lazy to break out an old text book and look.

[Max M3]

Given reasonable wall thickness, hollow is stronger. It's an engineering thing...

Which means, I'm too lazy to break out an old text book and look.

Yes, it's a physics thing....
If two bars are the same outside diameter, and same material, the tube will always be stronger than the solid bar.

[KozanBMW]

How.. i dont see it.

[BMW M Power]

i'm not an engineer, but i was always under the impression that a solid bar has 1 outside edge, whereas a hollow bar has 2 "outside edges" thus creating more surface area for added strength.


someone please correct me if i'm wrong.

[hc1001]

hollow is also lighter.

[RRSperry]

Ya made me go look it up didn't ya...

Maximum shear stress (tm)=(Torque [T])/Polar moment of inertia (Ip)
tm=T/Ip

substituting r=d/2 and Ip=Pi*d^4/32 you get
tm=(16T)/(pi*d^3) for a solid bar

For a hollow shaft, Ip =(pi*r^4)/2

Assume an inner raduis of .6r for the tube.
for the solid bar, the Ip = .5*pi*r^4

and for the tube Ip= (pi*r^4)/2 - (Pi*(.6r)^4)/2
= .4352*Pi*r^4

therefor the ratio of tm is .5/.4352 = 1.15 or, more plainly, the tube is 1.15 times stronger than a solid shaft, given the same outer diameter, and material.

Not only are they stronger, they are lighter too.

[denverlicious]

ok what you just showed me looks like ancient hebrew to me. is there a simpler explanation haha. basically hollow is better right?

[RRSperry]

God I love having an engineering degree...

[Jean-Claude]

Now you know for a fact no one knows what the heck you are talking about. :rolleyes


Ya made me go look it up didn't ya...

Maximum shear stress (tm)=(Torque [T])/Polar moment of inertia (Ip)
tm=T/Ip

substituting r=d/2 and Ip=Pi*d^4/32 you get
tm=(16T)/(pi*d^3) for a solid bar

For a hollow shaft, Ip =(pi*r^4)/2

Assume an inner raduis of .6r for the tube.
for the solid bar, the Ip = .5*pi*r^4

and for the tube Ip= (pi*r^4)/2 - (Pi*(.6r)^4)/2
= .4352*Pi*r^4

therefor the ratio of tm is .5/.4352 = 1.15 or, more plainly, the tube is 1.15 times stronger than a solid shaft, given the same outer diameter, and material.

Not only are they stronger, they are lighter too.

[RRSperry]

You should pay more attention to the instructor in mechanics of materials.
:redspot

[eneyeengee]

Now you know for a fact no one knows what the heck you are talking about. :rolleyes

i know what hes talking about
and i'm not a rocket scientist... yet ;)

[JClark]

Thanks RRSperry, nothing like a real life example to motivate me to get to work on my engineering homework.


Ya made me go look it up didn't ya...

Maximum shear stress (tm)=(Torque [T])/Polar moment of inertia (Ip)
tm=T/Ip

substituting r=d/2 and Ip=Pi*d^4/32 you get
tm=(16T)/(pi*d^3) for a solid bar

For a hollow shaft, Ip =(pi*r^4)/2

Assume an inner raduis of .6r for the tube.
for the solid bar, the Ip = .5*pi*r^4

and for the tube Ip= (pi*r^4)/2 - (Pi*(.6r)^4)/2
= .4352*Pi*r^4

therefor the ratio of tm is .5/.4352 = 1.15 or, more plainly, the tube is 1.15 times stronger than a solid shaft, given the same outer diameter, and material.

Not only are they stronger, they are lighter too.

[Matt M.]

Let me start by saying that I think the original poster's question is a little ambiguous, and that may be why this discussion took the course it did...

Stronger?

For a given diameter, a solid bar is stronger in torsion than a hollow bar. A greater diameter hollow bar can equal or exceed the torsional strength of a solid bar. It just depends on the wall thickness (i.e. how much material is missing out of the middle).



Maximum shear stress (tm)=(Torque [T])/Polar moment of inertia (Ip)
tm=T/Ip
.
.
.

therefor the ratio of tm is .5/.4352 = 1.15 or, more plainly, the tube is 1.15 times stronger than a solid shaft, given the same outer diameter, and material.


Tau Max isn't the bar's ability to resist torsion, it is the max shear stress that will result from an applied Torque. If you apply 5Nm of torque to a plastic straw and to a .25" diameter steel bolt, the straw will see a higher Tau Max. Doesn't mean it is better able to resist torsion.

Before you say it, I know.... 2 different materials. But that's my point; Tau Max is just a measurement of stress, not an indicator of the ability to resist stress. It doesn't take into account things like materials.

With constant OD, a tubular cross section has a lower polar moment of inertia than a solid one. We agree on that part. Keeping the applied torque a constant, dividing by the lower polar moment is how you end up with the higher Tau Max. Do it the other way; assume Tau Max is a constant related to the material's plastic deformation or ultimate strength point. Now the higher polar moment multiplied by the constant Tau Max gives a higher Max Torque before failure.

To actually see how the solid bar handles that stress compared to the tube, you need to picture the cross section. At the center point in the diameter of the bar, Tau=0. At the outer radius, Tau is at its Max. Tau increases linearly from 0 to max. Since the tubular cross section is missing a large amount of material that would otherwise do the job of resisting the stress near the neutral axis, the smaller annular area of the tubular cross section has to carry the same total load as the circular area of the solid cross section.

http://www.tripledistilled.com/swaybars.jpg

Image found via Google image search! Awesome!

Admittedly, the part of the solid bar that is missing with a hollow cross section is the part that resists a Tau closer to zero, so it does not have an overwhelming effect on the bar's ability to resist applied torque.

So....


...they are lighter too.

Even though the tubular bar isn't actually stronger, the advantage of the hollow cross section is a significant weight reduction without significant loss of resistance to torsion. In some (most) cases, this trade-off is worthwhile.

When comparing a solid sway bar with a tubular bar of identical material and arm geometry, you need to subtract the inside diameter (i.e. wall thickness times 2) to the fourth power from the outside diameter to the 4th power, and then take the fourth root of the whole thing.

In "Excel-speak", think (SQRT(SQRT((OD^4)-(ID^4))).

In practical-speak, I haven't seen a sway bar on a BMW break in years. If the original question about "strength" was due to a concern about breakage, don't worry. If you want to compare a tubular bar to a solid bar, then you just need to keep in mind what I said at the beginning: For a given diameter, a solid bar is stronger in torsion than a hollow bar. A greater diameter hollow bar can equal or exceed the torsional strength of a solid bar. It just depends on the wall thickness (i.e. how much material is missing out of the middle).

For a look at how a tubular bar's measurements will compare to a smaller-but-heavier solid bar, check out the page on UUC's E46 M3 sway bars: http://www.uucmotorwerks.com/html_product/sway_barbarian/html_sway_bar/description2.htm

If the manufacturer's whose tubular bars you are looking at doesn't have this kind of comparison page, email me and I will help you write an Excel spreadsheet to calculate it for yourself (TK Solver and Mathcad requests also OK).

BTW, while the bar geometry (width of straight portion, length of arms, position of adjustment holes/blade length, angle of arm to straight portion) has a huge effect on overall stiffness (i.e. effective spring rate), the material does not. The modulus of elasticity of different steels doesn't vary significantly.

--Matt

[Jean-Claude]

That's what i'm sayin'.


Let me start by saying that I think the original poster's question is a little ambiguous, and that may be why this discussion took the course it did...

Stronger?

For a given diameter, a solid bar is stronger in torsion than a hollow bar. A greater diameter hollow bar can equal or exceed the torsional strength of a solid bar. It just depends on the wall thickness (i.e. how much material is missing out of the middle).



Tau Max isn't the bar's ability to resist torsion, it is the max shear stress that will result from an applied Torque. If you apply 5Nm of torque to a plastic straw and to a .25" diameter steel bolt, the straw will see a higher Tau Max. Doesn't mean it is better able to resist torsion.

Before you say it, I know.... 2 different materials. But that's my point; Tau Max is just a measurement of stress, not an indicator of the ability to resist stress. It doesn't take into account things like materials.

With constant OD, a tubular cross section has a lower polar moment of inertia than a solid one. We agree on that part. Keeping the applied torque a constant, dividing by the lower polar moment is how you end up with the higher Tau Max. Do it the other way; assume Tau Max is a constant related to the material's plastic deformation or ultimate strength point. Now the higher polar moment multiplied by the constant Tau Max gives a higher Max Torque before failure.

To actually see how the solid bar handles that stress compared to the tube, you need to picture the cross section. At the center point in the diameter of the bar, Tau=0. At the outer radius, Tau is at its Max. Tau increases linearly from 0 to max. Since the tubular cross section is missing a large amount of material that would otherwise do the job of resisting the stress near the neutral axis, the smaller annular area of the tubular cross section has to carry the same total load as the circular area of the solid cross section.

http://www.tripledistilled.com/swaybars.jpg

Image found via Google image search! Awesome!

Admittedly, the part of the solid bar that is missing with a hollow cross section is the part that resists a Tau closer to zero, so it does not have an overwhelming effect on the bar's ability to resist applied torque.

So....



Even though the tubular bar isn't actually stronger, the advantage of the hollow cross section is a significant weight reduction without significant loss of resistance to torsion. In some (most) cases, this trade-off is worthwhile.

When comparing a solid sway bar with a tubular bar of identical material and arm geometry, you need to subtract the inside diameter (i.e. wall thickness times 2) to the fourth power from the outside diameter to the 4th power, and then take the fourth root of the whole thing.

In "Excel-speak", think (SQRT(SQRT((OD^4)-(ID^4))).

In practical-speak, I haven't seen a sway bar on a BMW break in years. If the original question about "strength" was due to a concern about breakage, don't worry. If you want to compare a tubular bar to a solid bar, then you just need to keep in mind what I said at the beginning: For a given diameter, a solid bar is stronger in torsion than a hollow bar. A greater diameter hollow bar can equal or exceed the torsional strength of a solid bar. It just depends on the wall thickness (i.e. how much material is missing out of the middle).

For a look at how a tubular bar's measurements will compare to a smaller-but-heavier solid bar, check out the page on UUC's E46 M3 sway bars: http://www.uucmotorwerks.com/html_product/sway_barbarian/html_sway_bar/description2.htm

If the manufacturer's whose tubular bars you are looking at doesn't have this kind of comparison page, email me and I will help you write an Excel spreadsheet to calculate it for yourself (TK Solver and Mathcad requests also OK).

BTW, while the bar geometry (width of straight portion, length of arms, position of adjustment holes/blade length, angle of arm to straight portion) has a huge effect on overall stiffness (i.e. effective spring rate), the material does not. The modulus of elasticity of different steels doesn't vary significantly.

--Matt

[RRSperry]

Right out of the Mechanics of Materials text.


Seeing as how shear stress, Tau, is related to shear strain (y) by Hook's law, in a linearly elistic material, we get Tau=G*y = G*r*Theta
Where G is the shear modulas of elasticity, and Theta is the angle of twist.

Torsional rigidity = G*Ip
G*Ip/L ((length) is the torsional stiffness, torsional flexability is the inverse.

Anyway, for bars made of the same material, and with the same outer diameter, assuming that the wall thickness isn't too thin. The internal stresses will be higher, in the hollow bar, but still below the allowable.

A hollow bar will resist torsion more efficiently that a solid bar! And has the added benifit of being lighter.

[Matt M.]

Right out of the Mechanics of Materials text.

I don't have any disagreement with your equations. But be careful about what you're actually solving for.

Here's where you started...



Maximum shear stress (tm)=(Torque [T])/Polar moment of inertia (Ip)
tm=T/Ip

Nothing wrong with that. That equation defines Tau Max as a function of the applied torque and the polar moment.

But Tau Max is just a stress in a single plane. Lower is better, with respect to the material's stress-strain curve. And you'd need to use Tresca or Von Mises to get a more accurate idea of the total distortion energy a sway bar is actually subjected to.

Then you wrote:



Assume an inner raduis of .6r for the tube.
for the solid bar, the Ip = .5*pi*r^4

and for the tube Ip= (pi*r^4)/2 - (Pi*(.6r)^4)/2
= .4352*Pi*r^4

We still agree on the polar moments...


therefor the ratio of tm is .5/.4352 = 1.15 or, more plainly, the tube is 1.15 times stronger than a solid shaft, given the same outer diameter, and material.

...but look at what you are actually calculating - you solved for Tau Max, not "strength". The tube isn't 1.15 times stronger, it has 1.15 times higher max shear stress at the outer radius.


Seeing as how shear stress, Tau, is related to shear strain (y) by Hook's law, in a linearly elistic material, we get Tau=G*y = G*r*Theta
Where G is the shear modulas of elasticity, and Theta is the angle of twist.


This is also true, but it doesn't take the applied torque into account. All this equation does is prove once again that the max shear stress at the OD is higher for a tubular member.

For a constant torque, i.e. the load applied by a car under cornering, R*theta will be greater with a tubular bar than a solid one. The tubular bar needs to twist farther to do the same job.... because it is weaker in torsion than a solid bar of the same OD!


Torsional rigidity = G*Ip

Once again, no disagreement from me.

But we already established that at a given OD, a tube has a lower polar moment than a solid bar, right?



Assume an inner raduis of .6r for the tube.
for the solid bar, the Ip = .5*pi*r^4

and for the tube Ip= (pi*r^4)/2 - (Pi*(.6r)^4)/2
= .4352*Pi*r^4

So for the same material (constant G), the lower polar moment of the tubular member produces a lower torsional ridigity. And you need to increase the diameter and/or wall thickness of the tube to get the polar moment and therefore the torsional ridigity to meet or exceed the behavior of the solid bar.


Anyway, for bars made of the same material, and with the same outer diameter, assuming that the wall thickness isn't too thin. The internal stresses will be higher, in the hollow bar,

True, regardless of the tubular bar's wall thickness...


but still below the allowable.

Whoa! Not necessarily true! Guys who design stuff for a living feel their stomachs turn when you say stuff like this.

If what you wrote were the case, then every engineer in the world could just design their driveshafts, halfshafts, crankshafts, propshafts, torsion bars, sway bars and other torsionally stressed members as though they were solid and then at the last minute substitute a hollow bar. I'm sure that the guys at Boeing will be thrilled when you call them with this news!

There are definitely cases where the max stress is so far below the deformation point for a solid torsion bar that the tubular bar will also not deform, and this is called bad design. It means that the engineer grossly oversized the bar. Any weight savings you would get from switching to a tubular bar of the same OD is a band-aid. The right thing to do is go back and resize the correct bar for the application.


A hollow bar will resist torsion more efficiently that a solid bar!

Richard, for two members of the same OD, one solid and one tubular, loaded in pure torsion, this just isn't true. Your equations aren't wrong, but the conclusions you're reaching with them are.

For what its worth, a tubular member is more resistant to buckling when loaded in bending. And a sway bar does see some bending loads, but without doing a VM calculation I am confident that they are insignificant compared to the Torsional stresses.

I am *not* saying there are no advantages to tubular torsion bars. But greater torsional strength than a comparable solid bar isn't one of them.

The Moment Of Inertia for a cross section indicates the member's ability to resist bending. But Polar Moment of Inertia, which we've been working with here, indicates the member's ability to resist torsion. We already agree on the fact that for a given OD, the tube has a lower polar moment. If we could just agree that the polar moment is an indicator of the member's ability to resist torsion, we'd be all set!


Right out of the Mechanics of Materials text.

Hibbeler? If so, I'll point you to some example problems so you see what I mean.

--Matt

PS - If the discussion above still isn't cutting it for you, here's another piece of marketing literature that illustrates solid vs tubular sway bars: http://www.whiteline.com.au/docs/bulletins/Hollow%20vs%20Solid%20Swaybar.pdf

[Max M3]

Damn, you guys are GOOD! Nice detail.
:)

[ICTBMW]

There is more to it than just torsional force that the sway sees.

Consider Loads:

Torsion
bending moment
shear
axial

You have to use the principle of superposition to break down all the forces and combine all the loads in one diagram to *see* the actual loading on the bar.

Material properties also need to be considered.

[tmoeller]

ya'll is so smart. I wes never mech fer yer book lernin and sech.

[95MMM]

ya'll is so smart. I wes never mech fer yer book lernin and sech.

lol :lol

i hated mechanics of materials...took it twice because i never went to class the first time...


NOW for a more practical thought:

Just buy the sway bar...who cares if it's hollow or solid. You should buy the hollow just because it is has a plain and obvious weight advantage.

The people that designed the sway bar have supposedly done all the engineering calculations. If they haven't and it breaks...claim warranty :D

[95beema]

lol :lol

i hated mechanics of materials...took it twice because i never went to class the first time...


NOW for a more practical thought:

Just buy the sway bar...who cares if it's hollow or solid. You should buy the hollow just because it is has a plain and obvious weight advantage.

The people that designed the sway bar have supposedly done all the engineering calculations. If they haven't and it breaks...claim warranty :D

Weight smate. I buy the shiniest one :stickoutt

[tmoeller]

Weight smate. I buy the shiniest one :stickoutt


Are you a raccoon?

[DLO]

Sure are some fart smellers on this board. Seriously though, great write up. Glad we have peeps like you guys on this board. Finally, a board where people know their sh*t!

D

[///Malcontent]

Assuming the same material, it all comes down to geometry, specifically sectional properties. And assuming the same diameter, a solid cylinder always has higher sectional properties (area, axial and torsional inertias) than a hollow cylinder. Simple.


There is more to it than just torsional force that the sway sees.

Consider Loads:

Torsion
bending moment
shear
axial

You have to use the principle of superposition to break down all the forces and combine all the loads in one diagram to *see* the actual loading on the bar.

Material properties also need to be considered.

[RRSperry]

Actually it was Gere & Timoshenko. In my defence, it has been a long time since then, and I have never really worked as a design engineer. Again, in my defence, I think I did later revise my statement to be, that the tube was more efficient.
But I yeild (he he) to you here.

[Def]

Yep - Matt M is right.

That said - the practical conclusion is that you should ALWAYS go with a hollow bar. You can make it just a "stiff" as a solid bar by slightly increasing the outer diameter, and you will have a tremendous weight benefit(sometimes as much as 7-10 lbs depending on the bar and material). If it's designed correctly, it will absolutely never fail so the fact that it is stressed slightly more than its solid breatheren is a non-issue.

[95MMM]

If it's designed correctly, it will absolutely never fail so the fact that it is stressed slightly more than its solid breatheren is a non-issue.

exactly, so buy the hollow since it's lighter

[badmonkey]

Anyone interested in a set of RD bars, PM me. RD bars are 27mm front, 24mm rear.
These are solid bars, adjustable, includes rear links, and all bushings.

John

[bndtechsource]

Hello all,

Based on the discussion from Matt M. I have put together an Excel calculator for solid ARBs (anti-roll bar, sway bar, etc.) It also contains a calculator for comparing tubular and solid ARBs. Please have a look. I welcome all comments.

http://bndtechsource.ucoz.com/load/suspension_design/tubular_vs_solid_arb_excel_calculator/2-1-0-7


Regards,

Bill

[pbonsalb]

Once you are done with the theoretical, could you work on the practical? Who makes hollow swaybars for our E36M3s? What is the weight difference relative to a comparable stiffness solid barr?

[dizzythree]

Who makes hollow swaybars for our E36M3s

Ground control.


What is the weight difference relative to a comparable stiffness solid barr?

My ground control bars weighed the same or less than stock.

Aftermarket, stiffer, bars weigh more.

[Brent 930]

Bimmerworld

[Matt M.]

Hello all,

Based on the discussion from Matt M. I have put together an Excel calculator for solid ARBs (anti-roll bar, sway bar, etc.) It also contains a calculator for comparing tubular and solid ARBs. Please have a look. I welcome all comments.

Bill,

Your tubular to effective solid diameter conversions are correct. But you may want to revisit the other worksheets in your spreadsheet.

I assumed the equations you used in your spring rate worksheets were sourced from Fred Puhn's "How to Make Your Car Handle", and the NASIOC thread you linked confirms that assumption. The derivation of that equation is a little murky, but you can consider it to be solving for the stiffness of the bar with a 1" deflection of one arm vs the other.

Analytically, modeling a sta-bar and doing a basic FEM analysis (allow the center to rotate but not translate in cartesian space, fix one arm, deflect the other) you will find three major components to sta-bar deflection - torsion of the lateral bar, bending of the longitudinal arms, and bending of the lateral bar. Puhn's equation neglects the third term (which is the smallest). Compared to an FEA output for a couple of test cases, this equation is accurate to within about 5%.

Sounds pretty good, so far. But then we get to the installation. What, exactly, does that 1" relative deflection mean?

First, in two wheel bump, there should be no relative deflection. Therefore the rate contributed by the bar is zero. So you may want to remove the bump worksheets entirely - if sta-bar acts in bump, it's called a z-bar (and as a result, doesn't act in roll). The only exception to this rule would be when the arm lengths differ from one side to the other (like choosing a different adjustment on the left vs the right), which would cause a difference in the left-right deflections.

Second, in roll, a 1" relative deflection would have to be comprised of compression on one side and extension on the other. That means that in order to actually talk about 1" of single sided deflection, you need to double the bar rate you calculated. And now, at the very best case, you have a motion ratio problem, and you must solve for wheel rate the same way you would for coil springs. Looking at the NASIOC thread, I see that the square of the motion ratio is incorporated into their STi-specific discussion, but with no pictures/references to back up the numbers, I would be wary. Motion ratios for sta-bar attachment points are a less commonly discussed (and thus less well-known) number than their coil spring counterparts.

With the wheel rates worked out, you can go back and calculate the effect of two wheel bump with unequal arm lengths, and also note the reacting force seen by the inside wheel in roll.

A couple of final thoughts:

If you were designing a chassis from scratch, and able to define a realistic target roll gradient, working with sta-bar deflections analytically would be hugely valuable. The value diminishes somewhat when you're in "tuning" mode.

Even at the OE level, it is not uncommon to test prototype bars in a simple jig that mimics the FEA - fix one arm, pivot the center, and deflect the other arm (with a load cell in series). This will often yield a multiplicative factor that can be applied to the overall vehicle model. The factor may have to do with rubber bushings, link elastic deformation, link installation angle, and even small variations in actual material properties vs the published numbers.

Finally, if you have a set of scales, the best practical approach may be to measure the roll stiffness distribution of your car in various sta-bar configurations, including unhooked, and then know with certainty what the sta-bar is contributing. Here's an example of that procedure: http://home.earthlink.net/~whshope/id14.html

--Matt

[pbonsalb]

Looks like twice the money for the same performance, with some weight savings. People buy $700 carbon fiber hoods. I don't think I would notice the difference enough for the hollow sways to be worth the money over comparable stiffness solid ones, but maybe a hardcore racer in a race car could.

[dizzythree]

I bought my GCs because they were $600shipped at the time and come with endlinks, and are very well designed. A very fair price IMHO.

[bigpuppy]

My tubular Ground Control anti-roll bars are quite a bit lighter than the Turner Motorsports solid bars I had before them. Do I notice the weight savings? Probably not. The advantage to the GC bars are the size options. I prefer having the ability to tune the suspension the way I'd like it to feel rather than purchasing a one size fits all set of bars. Ground Control has several size options available. I have the large front and small rear and the size of the front bar in relation to the rear feels MUCH better. I felt like the Turner rear bar was too big and it seems as though all of the solid bars on the market are very similar in size. To me it's not the wieght savings, it's the size options available allowing the ability to taylor the car to how you want it to feel that makes the the GCs superior. The weight savings is just a bonus. Hotchkis now makes tubular anti-roll bars for the E36 as well.

[bndtechsource]

Matt,

Thanks for your reply.

With a bit more searching I found a website with a calculator that gives all the information I was looking for (sometimes it's better not to reinvent the wheel). My main reason for creating an Excel spreadsheet was to have a calculator on my computer for those times when there is no internet access.

http://www.fromsteve.net/tech/Sway-Bar-Rate-Calculator

This calculator provides output for roll as well as one wheel bump for either solid or tubular ARBs. It also has a slide bar for choosing the desired motion ratio. And it has all the english/metric conversions available.

I agree with you that two wheel bump (of equal wheel travel) would negate the ARB effects on the wheel rate.

While 1" relative deflection may be easier for most to work into their overall wheel rate calculations, I thought having the ARB spring rate as a function of degrees rotation would be more meaningful.

As you can see from my website, I am using CATIA kinematics to work out my motion ratios for both the coil-over shocks and the ARB. This would also include the spring force delta resulting from the shock angle. Once I have this, I can the chart the data in Excel showing the wheel rates from jounce to rebound (in two wheel bump, one wheel bump, and roll).

Regards,

Bill

[bcbrad]

I just have to jump in real quick and say that I am in Mechanics of Materials right now... I hate that class! If anyone needs to reference to it, its all in chapter 5. Have fun.

[pbonsalb]

My tubular Ground Control anti-roll bars are quite a bit lighter than the Turner Motorsports solid bars I had before them. Do I notice the weight savings? Probably not. The advantage to the GC bars are the size options. I prefer having the ability to tune the suspension the way I'd like it to feel rather than purchasing a one size fits all set of bars. Ground Control has several size options available. I have the large front and small rear and the size of the front bar in relation to the rear feels MUCH better. I felt like the Turner rear bar was too big and it seems as though all of the solid bars on the market are very similar in size. To me it's not the wieght savings, it's the size options available allowing the ability to taylor the car to how you want it to feel that makes the the GCs superior. The weight savings is just a bonus. Hotchkis now makes tubular anti-roll bars for the E36 as well.

Most of the solid bars are tuneable also in that they have multiple mounting holes that affect the leverage. Similarly, you can buy bigger or smaller front or rear solid bars if you want. There are charts around with all the various sizes. I have a UUC front with an Eibach rear, for example. The front have 3 mounting holes on each side and the rears have two on each side. I also have adjustable endlinks front and rear. For me, the benefit would be weight savings. People have been known to spend a few hundred dollars to save 10 lbs and there is nothing wrong with that, or people put race spec parts on their street cars -- I have done this.

[dizzythree]

The ground control tubular bars come with their adjustable endlinks, and the front bars are adjustable by just loosening some nuts. You can adjust the front bar whilst the car is still on the ground.

The rear bar has holes for adjustment, and fits under the halfshaft perfectly. They are very well designed bars, I was impressed when I got mine. Much better than what I expected when I placed my order.

I probably would have gone with the Turners or the H&Rs if I didn't get the Ground Control, but I'm glad I did. The weight savings isn't their only benefit.