Pic of my custom rear strut bar

[pparaska]

The amount of force applied to either bar will be different, since they will have very different stiffnesses. The less stiff the bar, the less force will be seen at the joints, the lower the compressive stress, and the more the ends of the bar will be allowed to move towards each other.

 

If the point of the bar is to keep the towers from moving towards each other in response to suspension loads, it makes a very real difference in the force applied, and most importantly, to the amount of rigidity (or compliance) of those strut towers.

 

Those are the facts. I threw my credentials out to point out that I know what I'm talking about on this topic. Many years of engineering school, a masters' thesis, and years of experience on the job doing structural engineering DOES make me a bit more qualified that an network administrator on this topic.

 

But if you don't want to believe me, that's fine too. A snazzy chrome bar may be all you were looking for. I just wanted to point out to the readers of this forum that a curved bar is a BIG compromise is stiffness and rigidity (the reason most people put the bar there), one that needn't be made, since it's a straight shot between the towers. Unlike the situation with the L6 valve cover between the front towers, unless tall mounts are used at the towers, which also isn't the best design either.

[Jersey]

Pete, Pete.... PETE It seems your getting all fired up over nothing. I'm trying to put it in the simplest terms as i can but obviously i'm not succeeding by the way you're responding. I'll try again because i think this is a simple disagreement of opinion but you may be thinking i'm trying to take your credentials away, which i'm not. I do AGREE with you that a straight bar has more rigidity, and i know you have more education in structural engineering than i do. With the "Network Admin with family...blah, blah" signature, it was just to bust chops. Sorry if you took it the wrong way. Here's all i'm trying to say... i'll try this way with a question -

 

Do you think that the curved "sissy" bar that used, which is 1/16" thick and 1" OD, will flex at all by any amount of pressure that the shock towers can apply to it? I don't. If you do, that's fine and i respect your opinion. We just may have different opinions, that's all. Unless we have all the exact measurements of load/stress/strength etc. on the table, there's really no way we can come up with a definitive answer that this bar would be outperformed in it's specific duties than a straight bar, leaving us with basically just opinion.... and one snazzy chome bar I think this may be my last post on this because after all, i love this site, you are an admin, and you can ban me at any time from hybridz BTW, i see you're in the northeast like me - we should try to get some type of Z track meeting together up here. The west coast boys seem to be having all the fun! I missed SEZ this year but would love hook up with a bunch of Z's at a track before it gets cold. Let me know if you're interested. Truce? 8)

[Drax240z]

Do you think that the curved "sissy" bar that used, which is 1/16" thick and 1" OD, will flex at all by any amount of pressure that the shock towers can apply to it?)

 

I have a roll bar in the rear of my Z that is made from 1-5/8" mild steel, with a rear strut tower bar in a straight line between the towers. If I drive over very uneven surfaces (gas station curb for example) with my right hand backwards on the bar, I can feel it move with the chassis flex. I have NO doubt whatsoever that the forces the rear experiences when I am on the autocross track with stick rubber at 60mph is much greater.

 

You might be thinking that this is sortof irrelevant info because I am not feeling the bar flexing, but I am feeling what it is attached to flexing. This is very true, but what it is attached to is also 1-5/8" steel tubing, 0.120" wall.

 

Unless we have all the exact measurements of load/stress/strength etc. on the table, there's really no way we can come up with a definitive answer that this bar would be outperformed in it's specific duties than a straight bar, leaving us with basically just opinion....

 

This is like saying that unless you prove it with numbers, steel is lighter than air. It shouldn't have to be proven because it's essentially common knowledge.

 

Anyway, not trying to stir the pot really but I think the arguement is a bit silly.

[Jersey]

Drax, i think this is just a difference in opinion and a good possibility and a mis-understanding of what i'm trying to explain. I'm not argueing one bit and i hope that Pete doesn't think that.

 

In responce to your reply, I bet you can feel the rear bar move when the rear flexes, but they're flexing in the same direction when you feel it, not in opposite directions. Also, it's don't think it's common knowledge of what i stated -

 

Unless we have all the exact measurements of load/stress/strength etc. on the table, there's really no way we can come up with a definitive answer that this bar would be outperformed in it's specific duties than a straight bar, leaving us with basically just opinion

 

The "specific duties" i was referring to was in the back of a Z between the strut towers. I don't know what the amount of compression or expansion load is applied between the rear towers but, if it is common knowledge or posted somewhere that i missed, i apologize, i didn't know someone had measured that already. Maybe you and Pete both already know these values and that's why you cant understand my opinion?

 

Maybe here's an easier way for me to explain all i'm trying to say. If i grabbed a straight bar with my arms on both ends and compressed it with as much force as i humanly could and measured the amount the bar compressed, i dont think there would be any different results with the bar i used, just because the simple fact that i cannot apply enough force to compromise the bar. I just dont think that the rear towers apply the amount force it takes to comprimise the bar i used. Now if you incresed that force by 3, 5 or maybe 10 times the amount (guessing because i dont know the exact #'s), the bent bar i used will absolutely flex much quicker than a straight bar, i agree 100% with you both on that and i do know that is basic knowledge and a proven fact. I don't know how else to put it. I guess it's just hard for to explain sometimes what i'm trying to say here typing it.

 

I'm just trying to state my opinion, thats all. Not trying to argue and not meaning for anyone to get upset or pissed about this post. I now feel like going home, taking that bar out and smashing it into about a thousand pieces, just because. j/k. I like my snazzy chrome bar. It even has two threaded t*ts on top that i mount my camera to when i'm driving/racing

[pparaska]

Jersey, I'm not pi$$ed at all. It's just that when I see what I believe to be incorrect information (that a curved or straight bar will have the same effect in this application), I will respond. Part of the point of HybridZ.org is to have correct factual information in it's threads. If I were to not challenge a post I thought was technically incorrect, I'd be doing others that search on this topic or are reading the responses to it a disservice. Others should do the same when they see something they know to be incorrect.

 

I will disagree that this is a matter of opinion. Either the curved and straight bars have the same effect, or they don't. That's a matter of fact, not opinion.

 

Mikelly has posted many times that this place is about no-bs tech info.

 

After I return from vacation, I will pull out the books and apply the engineering theory to give equation and some examples of force vs deflection, etc. for the curved vs straight bar issue. I don't believe an instrumented test is really in order, but I suppose I could make up a curved bar to replace my straight one, and instrument the straight and curved bars, set up some datalogging and go for some spirited rides. MD has taken a OLD, BAD clue from New Jersey and installed a bunch of traffic circles. NJ desided to get away from them, but the geniouses in the MD SHA think they are the best way to deal with intersections. These really are fun when no one is around (but I hate to seem them in high volume areas). Almost like having skid pads put in by the state .

 

But for me, the theory alone will answer the question. I don't have time to instrument this test, but I'd love to see someone do it.

 

Don't worry, I'm not mad, and I'm not worried about my credentials being taken away. It's just that I don't want people to think that a curved bar is the way to go to make an effective strut tower brace.

 

BTW, Drax's test proves one thing to me. That you need the X brace to be effective. The towers move. If you push one with the other (using a rigid bar), then the bar will move (mostly side to side). Tieing the strut tops to the base of the opposite tower with an X brace would do away with some of that tower-top flexure. But since the Z is made up of thin metal it might not help much unless you spread the load quite a bit top and bottom.

[Jersey]

ok.

[2126]

I just love it when engineers have to tell you that....I have a degee in this and that and I have more experience in this that you do!!! (a little insecurity coming out maybe?) I'm not anyone of authority, however I work with and have worked with many an engineer in my life. The point being is that like every profession, there are people who are good at what they do and there are some that are less than shall we say...acceptable! Don't get me wrong here, my intent is not to insult anyone. But the fact of the matter is....for a given diameter and wall thickness, a strait section of tubing is stronger than a bent one, under compression and tension!!! So, why would one (especially an engineer)want to strengthen a structure with a bent tube, as opposed to a straight tube, especially when you don't have the figures on the loading to work with. Unless of course that said person just wants to have a novelty item.

 

Just one man's opinion! (I just love this site!!!)

[pparaska]

O.K., I'm a knuckle-dragging caveman with an IQ in the single digits. I'm more believable now, for sure!

 

No, I'm a navy engineering tech, and all those engineers don't know their slide rule from a yard stick. Yeah, that's it!

 

Tom, I worked in the civilian Navy (NSWCCD, Bethesda, MD) for 11 years, I know what you mean about engineers without a clue, as far as what real world loads are, etc. I worked with a few too. There are some really book-smart engineers out there that I wouldn't trust near anything I was building.

 

You see, I could give you as many examples of navy engineering techs without a clue as engineers - and some that effectively had engineering credentials due to their brain power and experience. My dad was like that too - an electrical engineering tech who had to teach the new engineers the ropes in practical radar design (JHU Applied Physics Lab - Radar Engineering). I was lucky. My dad's experience taught me that engineering techs were to learn from, not to be looked down on or to teach.

 

But I realize that to an engineering tech, an engineer splashing you with degree credentials means they might be insecure. That's a prejudice I've seen from navy engineering techs, without telling them my degrees. It's a cultural thing. I've seen the initial doubt of an unknown engineer by navy engineering techs first hand and second hand with new engineers hired after me. It's good for the smart-ass engineer right out of school that talks down to the engineering tech who knows much more than they do about a test setup, etc. I've seen a few of these cock-strong young bucks get knocked down a few pegs - to their betterment, once they managed to lick their wounds.

 

I was just trying to explain to Jersey that a curved bar is a inferior design for this application, and that if he wanted to disagree with me 100% about it, I was going to do the same, since I want HybridZ to remain a resource for correct technical information. It wasn't personal.

 

Funny thing is, I got more respect from the engineering techs there when they saw the work I did building my V8Z.

 

Pete - MSME - so I must not have a clue!!!!

[Pop N Wood]

Little girlie man strut bar. Can't even get a straighty.

 

[Jersey]

LOL. Thanks POP N WOOD Pete, no reason to break out all your books or make a curved bar or waste any more time on this. It's just my opinion that the rear strut towers will not apply enough force to compromise the curved bar I USED at any time. Another curved bar with different dimensions/charcteristics than what i used, sure, the towers may flex it. If you can't understand or accept my opinion, because there are NO FACTS here that the bar I USED will flex in it's current application, than so be it.

 

Disagreement of opinion is human nature and healthy but if you start to believe your own opinion so much that it becomes fact to yourself, i consider this a pretty closed minded person on specific subjects. A few of my closest friends are exactly like this and i battle with them all the time on many different subjects that are based on opinion, but they can't accept anothers opinion because they believe thier opinion is right and must be fact. Pete, i'm not saying this is how you are but you sure did remind me of them here

 

I'm not pissed, this was nothing personal and probably just a big waste of HybridZ's server space. BTW, i've worked on cars, trucks, boats since i was a kid, holding the flashlight for my father at the age of around 8. Please don't let the "Network Administrator" or "Husband/Father" titles scare you on my technical opinions

[Drax240z]

First off this is a technical discussion not an arguement. In my opinion that means it is void of emotion and therefore we can't be stepping on each others toes.

 

Maybe here's an easier way for me to explain all i'm trying to say. If i grabbed a straight bar with my arms on both ends and compressed it with as much force as i humanly could and measured the amount the bar compressed, i dont think there would be any different results with the bar i used, just because the simple fact that i cannot apply enough force to compromise the bar. I just dont think that the rear towers apply the amount force it takes to comprimise the bar i used. Now if you incresed that force by 3, 5 or maybe 10 times the amount (guessing because i dont know the exact #'s), the bent bar i used will absolutely flex much quicker than a straight bar, i agree 100% with you both on that and i do know that is basic knowledge and a proven fact.

 

Ahha! The problem with this logic is that the bar doesn't stay rigid until you pass some force value, no matter what force you apply to the bar it will move!

 

So if you apply X lbs force to your curved bar, it will deflect Y amount. If X is larger, Y is larger. A straight bar will deflect less than a curved bar under axial loading.

[JMortensen]

OK, so the question really is: How hard do you have to lean on a sissy before it gives in under the pressure.

 

I can tell you this much: The front bar made a MUCH bigger difference on my car than the rear bar. I'm sure that the culprit up front is those long frame rails hanging out there with no roof structure.

 

I think Jersey's point is that he probably isn't putting a significant enough load on the suspension to really flex the bar significantly. Pete and Drax say it is going to flex.

 

Bottom line from what I can tell is that Jersey is a drag racer. I'm not thinking that a strut tower bar was on the top of his list of mods, and probably isn't going to make a noticeable difference for him anyway. But he had this sissy bar and figured he'd make use of it in a creative way. Congrats for being creative Jersey!

[Pop N Wood]

So if you apply X lbs force to your curved bar' date=' it will deflect Y amount. If X is larger, Y is larger. A straight bar will deflect less than a curved bar under axial loading.[/quote']

 

Against my better judgment I will throw my hat into the ring.

 

So if I go down to Home Depot, get a straight piece of 3/8 inch electrical conduit and duct tape it between the strut towers, it will more thoroughly eliminate chassis flex then Jersey's girlie bar?

 

I don't think you guys are listening to each other. Jersey has already said he agrees a straight bar is less prone to flexing than a curved bar, all else being equal (thank you JohnC).

 

So the question is when is enough enough?

 

Surely you have to agree that the curved bar is better than no bar at all? Kind of hard for me to see how you can categorically state that his girlie bar won't do the job without making some assessment of Jersey's suspension, driving style and potentially budget.

[Drax240z]

So if you apply X lbs force to your curved bar' date=' it will deflect Y amount. If X is larger, Y is larger. A straight bar will deflect less than a curved bar under axial loading.[/quote']

 

Against my better judgment I will throw my hat into the ring.

 

So if I go down to Home Depot, get a straight piece of 3/8 inch electrical conduit and duct tape it between the strut towers, it will more thoroughly eliminate chassis flex then Jersey's girlie bar?

 

I thought it was obvious I meant all other things being equal. Ie: Same OD, wall thickness, material etc.

 

Given Jersey's application I am sure it is all the bar he needs. However, consider this:

 

A close friend was sideswiped in his Z about 4 years ago, the thing that saved his life was his rear strut tower bar, otherwise the truck that had hit him (just behind the drivers door) would have done significantly more damage. Now, Jersey's bar may well be strong enough for that application, but...

 

Certainly it is better than nothing. Certainly is is a great use for an otherwise hideous piece of Datsun. And certainly a straight bar is stiffer! (all else being equal)

[pparaska]

As long as someone thinks that Newtonian physics applied to something that is travelling no where near the speed of light is opinion, I'll stand my ground. Equations based on Newtonian physics, geometry, etc. describe the bending, compression, buckling of straight and curved bars are things that were figured out 100s of years ago.

 

To say that you have an opinion about how they will react in you situation won't make a difference, without understanding the simple relationships and equations that dictate their reaction being linear as to the applied loads is where this discussion has gone wrong. Maybe you think the loads you'll apply to the curved bar are low enough that it won't matter. That's your opinion. Why not listen to someone educated in the field and let them tell you it might? Why hold onto an opinion that is not based on anything but your gut feel? That's your position, fine. But don't call my position opinion. It's based on fact.

 

I stand by my original assessment. The chromed curved bar used where a straight shot is available is just a snazzy camera mount. Sure, it doesn't weigh much and the camera might not care if it's moving up and down a little bit as the suspension loads flex the bar. The application is fine.

 

All I was trying to do is point out to others that might read this thread that looking for a solution to DIY strut bars consider the compromise being made.

 

Then my factual post was called an opinion and my use of my credentials were thrown back at me.

 

Again, I'm posting from a position of fact based on physics. It is not an opinion.

 

I won't back down when facts are being questioned or called opinions. Some might think that's "dragging it out". As long as factual posts are being called opinion because it doesn't match the uneducated guess and opinion of someone else, especially here on HybridZ, I will run the discussion for as long as needed. The non-factual based opinion will not stand as the last word. The FACTS will.

 

Pop - actually, I don't know if the curved bar will do anything appreciable to holding the towers apart. A curved bar, in almost any configuration that's using a 1"-ish diameter thin steel tube, with 3 or 4 inches of eccentricity to the load direction is going to be quite flexible. It may actually not do much at all towards holding the towers apart under hard cornering or a hard launch.

 

Jersey, if you're friends are arguing with you based on what they say are factually based points of view, consider researching their "facts". You might learn something and find that you agree with your friends.

 

Yeah, I'm now busting your chops. They need it. You continue to state that what I'm saying is opinion. It's FACT. As long as you do that, I'll run this thread on for as many pages as needed.

[Mikelly]

 

Oh my peter...

 

Christ this is funny!

 

OK, so I'm assuming (God help me here) that the intent of the bar is ONLY for the purpose of holding a camera, and if that is truly the case then, Great, should serve the purpose of the intent, which is to hold a 2 pound VHS-C type camcorder. (Don't throw anything at me just yet Pete! )

 

So, my question is (And I'm guilty of browsing the thread, more than reading it) what is your intent of the car? If it is gonna be a street car only, with no bone jarring suspension, no sticky tires and no aggressive hard romps, then I'm sure it would be sufficiant to hold a camera.

 

That said, I'd heed Professors Paraska & Drax lesson on structural integrity!

 

Hahahaha!

 

And Jersey, Sign up for the Summit Point FATT on September 10th... You and Pete both... I want to show both of you my taillites!

Mike 8)

[JMortensen]

Pop - actually, I don't know if the curved bar will do anything appreciable to holding the towers apart. A curved bar, in almost any configuration that's using a 1"-ish diameter thin steel tube, with 3 or 4 inches of eccentricity to the load direction is going to be quite flexible. It may actually not do much at all towards holding the towers apart under hard cornering or a hard launch.

 

You mean holding the towers together during hard cornering, right Pete?

 

http://e30m3performance.com/myths/Strutbar_Theory/strut_bar_theory.htm

[Drax240z]

 

You mean holding the towers together during hard cornering' date=' right Pete?

 

http://e30m3performance.com/myths/Strutbar_Theory/strut_bar_theory.htm[/quote']

 

Jon, from the page you linked:

 

I have heard of incidents where the strut tower bar was instrumented with strain gauges as the car was driven around. These tests show the strut tower bar is under compression as well as tension, depending on what the car is doing. One test showed that the highest loads recorded on the strut bar were in compression as the car was pulling out of a garage (sideways down an inclined driveway - we have all heard a stiff car twist under this condition).

[JMortensen]

I know, I know Drax. It also says that straight bumps will flex the towers together. Really they flex all over the damn place, and should be tied into a roll cage or bar to keep them from flexing fore and aft too.

 

Pete said

...It may actually not do much at all towards holding the towers apart under hard cornering...

 

I was just busting his chops a little. Sorry Pete, couldn't resist.

[Jersey]

Sounds good Pete. I will continue this conversation as well until you accept the FACT this this conversation is based on OPINION and that our OPINIONS on this discussion are just different.

 

Obviously, you are stuck on thinking i am challenging Newton's law or some other article of FACT but no, no i'm really not. I don't understand why you can't comprehend what i'm trying to say? You do at one point and then start throwing your education and Newton in the mix, which cannot be applied to our discussion at this time since we do not have ALL the facts.

 

As long as someone thinks that Newtonian physics applied to something that is travelling no where near the speed of light is opinion, I'll stand my ground.

 

Ummm,??? Sorry, i dont remember saying anything like that? And why would i when that information is FACT?

 

You say here:

 

Maybe you think the loads you'll apply to the curved bar are low enough that it won't matter. That's your opinion.

 

YES. Exactly what i'm trying to say. I do not believe the loads applied by the rear towers will compromise the bar i used. You understood my OPINION on this whole discussion right here. This has been exactly what i've been saying from the beginning. Perfect.

 

But then you continue to say:

 

Why not listen to someone educated in the field and let them tell you it might?

 

I do listen, you should try it as well. You can have all the education in the world and your OPINION will still not become fact. I hope you know this. I believe some of the friends i debate opinions with on a regular basis do not know this sometimes I do accept your OPINION and have said that many times. Maybe you were'nt "listening" You used the correct word here - MIGHT. It MIGHT, or MIGHT NOT. See, it's a difference of OPINION. What you don't understand is that this conversation is because you can't understand that this is just a difference in OPINION because we do not have all the exact figures to make it a fact that the bar i used is just as strong as a straight bar i used in this application we're applying it to which is between the rear strut towers of an S30, or it's not. It's really that simple.

 

Why hold onto an opinion that is not based on anything but your gut feel? That's your position, fine. But don't call my position opinion. It's based on fact

 

First, i hold onto my opinion because we don't have enough information to make this fact. And if you'd like me to change my opinion based on your education and/or any other credentials that you've stated, it's not going to happen. Why? because we do not have all the exact figures to make it a fact that the bar i used, in this application we're applying it to which is between the rear strut towers of an S30 is just as strong as a straight bar, or it's not.

 

Am i sounding like a broken record yet? If so, GOOD I'm hoping you, and possibly the other readers that may be confused on our discussion, will understand what i'm trying to explain here.

 

I will not listen to your OPINION beacuse that's all you're going on. UNLESS you know the exact mesurement of load the rear towers apply. If you do know these, i stand corrected and my OPINION is out the window. If you don't know these values, you have an opinion on this discussion as well. You THINK the loads are great enough to compromise the bar i used. I DO NOT THINK they are great enough. See? Both opinions. This isn't about last word Pete. What i really think this is coming down to is that you're either trying to make fact out of your OPINION or you just cannot understand my OPINION.

 

I do not argue with my freinds Pete, we have differences of OPINIONS. When there is fact involved, i do not argue against something that has already been proven. That's common sense. What they do is tend to state their opinions so strongly that they actually believe them to be facts, which you seem to be doing the same here. At 36, i am always learning and am always willing to learn. You should try it even with all the education you have. Have you seen me throw in my credentials of all the years of education or field experience i have? No. Why? Because what i'm trying to state is based on my OPINION.

 

Busting chops is good. Believing that your OPINION is actually FACT? Not so good. I accept your opinion Pete. What would be nice and we coould put this whole discussion to bed is if you accepted mine. But if you can't, it would be nice if you could just admit it that you ca't, and i'd understand, nad we'd be done here.

 

I think I just figured out a way that maybe i could have ended this a page ago:

 

If you CAN answer these questions with exact figures, i stand corrected because i wasn't aware that these values existed, and i aplogize. If you CANNOT answer these, then all you are going on is your OPINION.

 

What amount of load is applied between the rear strut towers in an S30, in any driving condition - dragging, autoX, etc.?

 

How much force needs to be applied to the bar i used to start compromising it?

 

If we had both of these figures, we could plug them into proven equasions and deterime which of our OPINIONS is correct.

 

Just a difference in opinion Pete.

 

Looking foward to your responce.

 

PoP N Wood - you are crackign me up over here. lol. And lay off the "girly" stuff. It's a SISSY bar lol.

 

Jon - you've got it -

 

I think Jersey's point is that he probably isn't putting a significant enough load on the suspension to really flex the bar significantly

 

But i think in any application, not just dragging. Although, thinking about it, a hard launch may put the most amount of compression stress on a rear bar because the tops of the strut towers will be pressing toward each other, rather than in the same direction when cornering. And thanks for the props. It was fun just to figure out that i can make it work for something on the Z, otherwise it was going to the junks. I spent more time typing and reading this forum alone than it took me to create it! lol.

 

Mike - If we meet up at summit point, i may have to swap out my rear bar to a straight one. That way i'll be somewhat competitive lol. j/k. But i do like the sounds of racing with some other Z's! Anytime.