User 41221

Because I have no life, I think I am going to try to see just how effective my strut brace is. I am planning on testing it by welding a slotted metal bracket onto a bolt that is the same thread as what currently goes into the brace rod. I will hit the bracket with a light coat of cheap paint and then bolt it onto the STB bracket on one side so that it is secured but will move freely. Then I will find a parking lot where I can execute a series of hard left and right turns, and then look to see if there is any paint worn off the bracket, indicating movement in the brace rod. If there is, that *should* be the amount of movement between shock towers, correct? Hopefully this doesn't become a measure of my welding skills, or lack thereof.

I am currently running on crappy tires, with monoballs, Bilsteins, 250# springs and 968 M030 swaybars on an '86 951.

Anybody see any flaws in the plan here? I might try a similar test the spring at a DE, if I think there is any merit in it. It would be fun to do this on track tires as well, and do a comparison, but I don't really feel like lugging them out of winter storage.

Regards, ...Scott

Z-man

Something to consider: if you allow the STB to move freely enough, you could put dimples in your hood due to the STB hitting up against your hood. There really isn't much clearance there.

But your idea sounds good: a real world STB test! If your setup is function, you can test the results at an autocross as well: there you can get some real numbers!

Good luck!
-Z.

slevy951

Sounds like a plan to me. Like Z-man said, keep the slotted part "thin", there isn't much left under the hood....

Thaddeus

Your methodology sounds correct to me as well. Let us know what you find out. Even a 1/8 inch amount of movement would be significant, methinks.

Be careful with your hood!

User 41221

If my shock towers are moving 1/8", I will be selling my car! I am thinking millimeters here, not large fractions!

Thanks for the reminders to watch hood clearance... anybody want to bet me that I will forget anyway? lol

Regards,...Scott

SidViscous

What you really want to do is get a strain gauge. Attach that to your strut brace with it fully attached (no movement of the ends. That will tell you the actual stress the strut brace is under. Right setup and you could do it real time. There are about amillion different types of straingauges you could use, varrying in cost.

Ideal setup would be a fiber optice Faby-perot strain gauge so that you could read it in real time.

Micro-sensitive potentiometers or encoders would be handy too but would require some conversion factor.

Your method is much cheaper but will give minimal results and don't take into consideration friction and give inthe strut brace. All you will be able to do is confirm if there is movement, and even then you won't be able to determine when or why you are getting movement.

Manning

Damn Sid, you beat me to the punch. More complicated for sure, but much more accurate.

SidViscous

If anyone wants to do this they can contact me as I have loads of experience in this area. won't be cheap but if Huntley, or Anderson want to get some real data I can help.

Company I consult with even did high speed video of the valve train for Ferrari's F-1 team.

User 41221

I knew someone would be able to burst my bubble here...

Lets see... get a strain gauge, custom build a new bar to run across the mounts that accomodates the newly purchased strain gauge (needs to measure somewhere in the middle of the bar, rather than at one of the ends to get an accurate measurement), set the gauge to read "zero" at rest, and then go driving, and read the results, right? Did I miss anything?

I played with these sorts of things while I was at University of Kansas (Mech Engineering). Using my previous method, the strut brace would only be pinned on one side, it should have "zero" stress in it (real world measurements would include such concepts as "friction", which I am choosing to ignore as minimal for this test), so the only thing I am really measuring is lateral movement, correct? Assuming I can accurately record and measure any movement along the slider that I am building, haven't I captured everything I need to know about whether a strut brace would be useful for our purposes? Granted, if I were wanting to find out how strong a strut brace I needed to build to limit movement, then strain becomes relevant, as I am sure the strut brace has elasticity under a load, but to what extent it stretches isn't really the question, at least not for now.

Sid and Mike, feel free to beat this concept up a bit. All I want to do is qualify the concept of a strut brace, not quantify the amount of stress, but you guys obviously have a good idea about how to do that, and since I have no life, I might pursue that as a secondary goal.

Keep the ideas rolling...

Regards, ...Scott

SidViscous

Using your idea of lateral movement. Before you start out.

How much lateral movement would be an issue for you to say a strut brace was needed?

As to install if the gauge needs to be mounted in the middle then your strut brace isn't strong enough and it's bowing. Which would greatly skew your results. Mounted anywhere should be fine. If your determing if a strut brace is needed any strain above X would show that the strut brace is countering the movement of the shock towers. Any strain would show movement, but something above X would show that the strut brace is fighting serious movement.

If you want to quantify the need it's really the only way. Otherwise what your doing a little more than I installed my strut brace and it feels better. There will always be movement of some kind. It's a matter if it's to much or not.

As to zeroing the gauge it doesn't exactly work like that

Depends on if your measuring pre-load stress, pre-loading the crossmember, Installing unloaded or otherwise. Strain is always a measurement of + or - from install. When you install whatever reading you get is zero. Ideally what you do is pre-load the gauge to be in the middle of it's range so that you can get accurate measurement in both directions. If you know for a fact that the movement is only going to be in one direction then you can bottom out the gauge and get extended range. In your case however I think your going to find movement 75% in one direction and 25% in the other.

And no your not just measuing lateral movement. In your setup if one shock tower deflects upwards, say the anchor tower, you will se movement in the measuring tower. Same if the shock tower moves forward or backward. Which in of itself would be usefull info showing that you need a trianglar crossmember instead. Point is you have no way of knowing which direction of travel is causing the proble, Wheras strain gauges are axial.

SidViscous

Ps in your plan if your through bolt tilts at a camber and can lock into place, utilizing the cross piece as a cross strut showing no movement and no need for a cross strut.

If your going to do it use a two piece anchored at each end and sliding in the middle.

944Fest (aka Dan P)

I'm glad someone is going to test this, somehow. I think he may have gotten this from my idea in the KLA stut brace discussion. Anyway, I'm looking forward to some results, scientific or otherwise, to finally lay to rest some of the strut brace questions.

THANKS!

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

User 41221

Honestly, I am constantly amazed at the quality of information available on this board. I submit to your expertise, Sid.

k, so my methodology isn't redhot... anyone want to take a guess as to whether this is really worth pursuing? I am not inclined to buy a strain gauge and manufacture a test bar just for grins, and since I have no intentions of starting to manufacture strut braces, I am thinking that this is quickly becoming a non-starter for me. I could see a Huntley, AMW or KLA wanting to do this, assuming they could show that STB's are effective. I was wanting to just prove, primarily to myself, whether it did have an effect or not.

Regards, ...Scott

SidViscous

Hey if you want to do it for kicks.

But to be honest your test setup was only about this much || away from being a strut brace. So why not just make a strut brace and be damned wether or not it's needed.

To satisfy your cuoristy and in a sense fo fair play I'll see if I can get you a strain gauge and readout.

thomschoon

Gee I thought his original idea would work for an indicator that there was movement. only difference is that I would take the bar off, clean it well and spray it with a lacquer coat(such as used in strain testing) and then get a very rough idea of what is happening from the crack pattern.

But then I drank my way through my undergrad