Sway bars

[sperry]

Originally Posted by cody

Monkey, the point of a RSB is to share the force flex between both strut towers. I fail to see how the pivoting joints take away from the usefulness of the bar. I wouldn't expect the bar to do anything other than keep the two strut towers at one constant distance from eachother (therby sharing the force exerted upon them). I think expecting a solid bar to keep the rear end "square" is asking too much of it.

I've got this awesome rope pool cue I'll sell ya, it's highly transportable, all you have to do it wind it up and put it in your pocket!

...you can't have hinges in the bar if it's gonna work. That's why you need to torque down the mounts. And even then, it's not going to be a good as a welded in bar, but that's a little impractical.

[cody]

So you disagree that the main point of a strut bar is to keep the tops of the strut towers at a static distance from eachother then Sperry?

[Nick Koan]

I believe the strut tower brace is not only for lateral distance, but vertical distance (or lack thereof).

A STB with hinges will acomplish the first goal, but not the second.

[AtomicLabMonkey]

Originally Posted by cody

I think expecting a solid bar to keep the rear end "square" is asking too much of it.

No, it's not asking too much, because that's exactly what you want chassis bracing to do. When you drive a car on track most of its time in corners is spent with a combination of braking, acceleration & cornering loads acting on it. This twists the chassis torsionally. The biggest gains in suspsension sensitivity & handling improvement/better feel for the driver come when you improve that car's torsional rigidity. Braces with pivoting joints will do very little towards that end.

[sperry]

Originally Posted by cody

So you disagree that the main point of a strut bar is to keep the tops of the strut towers at a static distance from eachother then Sperry?

Sure, that's what it's for, but if the bar pivots at the mounting point, you might as well just use a come-along and winch the strut tops together w/ a strap since you're only restricting the distance in one direction.

[cody]

Originally Posted by sperry

Sure, that's what it's for, but if the bar pivots at the mounting point, you might as well just use a come-along and winch the strut tops together w/ a strap since you're only restricting the distance in one direction.

The bar does restrict the towers from getting closer together and further apart...that's two directons.

[cody]

Originally Posted by AtomicLabMonkey

No, it's not asking too much, because that's exactly what you want chassis bracing to do. When you drive a car on track most of its time in corners is spent with a combination of braking, acceleration & cornering loads acting on it. This twists the chassis torsionally. The biggest gains in suspsension sensitivity & handling improvement/better feel for the driver come when you improve that car's torsional rigidity. Braces with pivoting joints will do very little towards that end.

Oh, because I assumed the biggest gains would be from maintaing suspension geometry. In this particular application, the bar inhibibits the wheels from losing negative camber due to latteral forces associated with cornering by sharing the forces between two strut tower instead of one.

[khail19]

I think a hinged strut bar provides some benefit as far as suspension geometry goes, but a solid bar also adds chassis stiffness as well.

[cody]

Originally Posted by nKoan

I believe the strut tower brace is not only for lateral distance, but vertical distance (or lack thereof).

A STB with hinges will acomplish the first goal, but not the second.

According to the link I posted earlier:

Figure 1 shows the forces of interest in a strut bar analysis. For this calculation only horizontal forces need be considered. There are of course vertical forces, but since the sum of forces must independently equal zero in both the horizontal and vertical directions, we can concentrate on just the horizontal forces in this analysis.

and...

What a strut bar does is tie the two strut towers together so that they share the load applied at the outer tower. This gives you twice as much material to deal with the same cornering force and helps reduce fatigue stress in this area.

[cody]

Originally Posted by khail19

I think a hinged strut bar provides some benefit as far as suspension geometry goes, but a solid bar also adds chassis stiffness as well.

I'm sure that's true to some extent. In fact, I should say the same thing about all everyone else's posts...except Sperry's.

[sybir]

Originally Posted by cody

Monkey, the point of a RSB is to share the force flex between both strut towers. I fail to see how the pivoting joints take away from the usefulness of the bar. I wouldn't expect the bar to do anything other than keep the two strut towers at one constant distance from eachother (therby sharing the force exerted upon them). I think expecting a solid bar to keep the rear end "square" is asking too much of it.

As much as this is fun to watch, it behooves me to point out that you're trying to argue suspension theory and chassis bracing with a guy who's day job is designing suspensions for race cars

That said, a rear strut bar helped add a little torsional rigidity in the back of my wagon, as I can no longer hear the hatch twisting around during hard coornering like I could before....but that's a much bigger car with a much bigger hatch area than WRX wagon. I knew the QR's were a sacrifice, as you can't even tighten them effectively, let alone tension them with Whiteline's conventional threading.

And if you're saying the bar feels stiff, therefore it's helping, think about how stiff your suspension towers feel already......are you able to just swivel those around?

Strut bars are just a minor band-aid fix for larger dynamic issue that can only be effectively addressed with a welded-in, tensioned, triangulated brace.

[cody]

Originally Posted by sybir

As much as this is fun to watch, it behooves me to point out that you're trying to argue suspension theory and chassis bracing with a guy who's day job is designing suspensions for race cars

That said, a rear strut bar helped add a little torsional rigidity in the back of my wagon, as I can no longer hear the hatch twisting around during hard coornering like I could before....but that's a much bigger car with a much bigger hatch area than WRX wagon. I knew the QR's were a sacrifice, as you can't even tighten them effectively, let alone tension them with Whiteline's conventional threading.

And if you're saying the bar feels stiff, therefore it's helping, think about how stiff your suspension towers feel already......are you able to just swivel those around?

Strut bars are just a minor band-aid fix for larger dynamic issue that can only be effectively addressed with a welded-in, tensioned, triangulated brace.

I know he's a suspension engineer. I just think that saying a STB with a hinge is useless is exagerating. I'm not arguing as much as trying to bate him into educating me.

And no, I'm not saying that the fact that it's stiff is helping. I'm saying that the fact that it keeps the strut towers at a static distance means force is shared between two strut towers instead of one.

[khail19]

I think strut bars got popular because the aftermarket made them for cars that needed them first, maybe like old Civics and whatnot. Then everyone decided they wanted them for looks mostly, because most newer cars don't benefit much from them. Cars chassis stiffness has increased so much in the last decade that it's mostly a bling item now. Of course, the manufacturers will be happy to tell you other wise, but I couldn't really notice when I put mine on.

[AtomicLabMonkey]

Originally Posted by cody

Oh, because I assumed the biggest gains would be from maintaing suspension geometry. In this particular application, the bar inhibibits the wheels from losing negative camber due to latteral forces associated with cornering by sharing the forces between two strut tower instead of one.

Assumption... incorrect. The primary reason for stiffening a chassis is so the suspension springs, dampers & swaybars control a larger portion of the vehicle's kinetics - instead of the chassis acting as an additional spring. This leads to more predictable handling, and better, more noticeable response to suspension adjustments. Wheel alignment control is only a secondary benefit.

[Nick Koan]

Originally Posted by cody

According to the link I posted earlier:





and...

True, but that whole article assumes that the strut towers are infinitely strong in the vertical direction. Which obviously is untrue. He is mostly correct, though, in saying that the horizontal forces are quite a bit larger, and there is also less strength bracing for horizontal forces. For the most part, having the bar in there with QR's is probably not totally worthless, but a solid bar would be better if you were trying to eek out every bit of performance.

[cody]

Originally Posted by AtomicLabMonkey

Assumption... incorrect. The primary reason for stiffening a chassis is so the suspension springs, dampers & swaybars control a larger portion of the vehicle's kinetics - instead of the chassis acting as an additional spring. This leads to more predictable handling, and better, more noticeable response to suspension adjustments. Wheel alignment control is only a secondary benefit.

I absolutely believe everything you wrote there, but you still haven't offered any evidence that a non-hinged STB does a better job at preventing the chassis from acting as a spring. I know it seems like it would to a certain extent, but any tiny amount of flex in the bar is going to negate the "stiffness" your depending on to hold the chassis "square". However latteral forces aren't really affected much at all by this flex.

[AtomicLabMonkey]

Originally Posted by cody

I absolutely believe everything you wrote there, but you still haven't offered any evidence that a non-hinged STB does a better job at preventing the chassis from acting as a spring. I know it seems like it would to a certain extent, but any tiny amount of flex in the bar is going to negate the "stiffness" your depending on to hold the chassis "square". However latteral forces aren't really affected much at all by this flex.

It's pretty simple; pinned joints can't resist moments (torques), but bolted/preloaded and welded joints can.

To keep with your square box analogy, if you have 4 pinned joints at each corner of the box, it will fall down if you push on the side of the box. If the 4 corners have rigid joints instead, it will stay standing if you push on the side of the box. I'll have to refer you to a statics textbook to get much more detailed than that.

[cody]

I'm just saying, it better be a VERY stiff joint to keep the box square. Thanks for humoring me.

[AtomicLabMonkey]

Originally Posted by cody

I'm just saying, it better be a VERY stiff joint to keep the box square. Thanks for humoring me.

No problem. Think of it this way - with rigid joints you at least have something resisting torque loading, vs. nothing with pinned joints.

Obviously it's not ideal; in an ideal situation you would only have pure tension/compression loadings in your structure. This is only possible when you start adding tubes which criss-cross the car, a.k.a. the roll cage.

[cody]

Right, everything about my car is a compromise starting with the fact that it's a "sport wagon". Every mod I have and will ever get shant take away from the versatility of the vehicle.

[MattR]

Good discussion boys..god damn....

So, wait until I tell you that I'm running no rear bar on the Sti. Double adjustable Coilovers and 8k springs FTW.

[sperry]

Originally Posted by MattR

Good discussion boys..god damn....

So, wait until I tell you that I'm running no rear bar on the Sti. Double adjustable Coilovers and 8k springs FTW.

You took off your swaybar?

[khail19]

Originally Posted by sperry

You took off your swaybar?

Aren't we talking about strut braces? It sounds like he took off his swaybar.

[cody]

Originally Posted by sperry

You took off your swaybar?

Pretty sure he meant rear strut tower bar. The sedan doesn't really need one anyway.

[MattR]

Originally Posted by cody

Pretty sure he meant rear strut tower bar. The sedan doesn't really need one anyway.

Nope, I meant my swaybar. I am in new territory of suspension tuning...we shall see.