mitchntx

Excellent post. An "a-ha" moment ...

You are correct, the lower ball joint or the end of the lower A-arm , is the fulcrum. I see that. Excellent point.

It appears, though, we differ in opinion about where the forces travel.

I still contend that because of the vehicles forward momentum and the front wheels being turned, the forces generated are sent more rearward than lateral. Hence the reason for the A-Arm to be an "off-set" A.

The forces you describe would no longer be sent across to the other SHOCK (not strut) tower, but more forward. Correct?

As far as putting a STB on a Miata ... well ... there isn't much there to begin with.

jrtf83

WOW! This thread made me really realize how little i know about suspension forces. I need to read up. that and climb under my car and examine some stuff up close. GREAT THREAD! Hey mods, think we could sticky it? This is a good debate.

Z28barnett

I appreciate the post readers comments about the debate, but I should point out that is really we are showing how little we know about what is happening in the front suspension. This is why people should be careful with the stock is junk attitude. The guys who built this thing were pretty crafty and when you mess with their stuff, anything can happen.

Back to the debate,

Without a braking load the forward momentum of the car has no effect that I can think of on the side loads of the car. Crusing down the highway at 80mph on smooth road the front lower and upper suspension arms are loaded the same as the car sitting still. Plus some drag and lift from the air flow and drag from the tires and wheel bearings.

A wheel at full lock does change the nature of the forces. The angle of the wheel from the centerline of the car's forward motion turns the simple forces and moments into vector sums.

Since the lower ball joint can rotate in any plane. You can break the new loading into two forces and two couples.

The forces to the front and rear will go into the k-member, and their moment loads will go to the upper ball joint and create reactions at the upper a-arm just like the side loads did but to the front or back insted of side to side. The STB will not help much with these loads, it would twist like a torsion bar.

I am estimating here but the wheels are by eye about 30 degrees from straight ahead when they are turned full lock. the sin or cosin of the angle with give you the percentage of the load front to back compared to the side to side. I would have to draw a diagram to really get this right but no more than roughly 30% of the total force would be directed to the front and rear direction. The remaining 70% would be a side load. So I would maintain that the STB bar would help with the majot part of the load 70% verses 30%. At lower steering angles you will have more side load and less front to rear.

The lower control arm is a bit of odd design. I just put new ones on with 1LE solid rubber bushings rather than the windowed stock bushings with half their mass cut away.

The design of the lower control arms is more about alignment and comfort than performance.

The wide base of the LCA allows softer bushings to take the load and stops the impact noise and vibration better. With the solid rubber bushings that has changed greatly. The wide spacing gives the bushings leverage against the loads and they can be softer for better ride without hurting handling as much as narrow spaced a-arm bushings.

The camber is mainly adjusted at the front LCA mount. The rear being 2' away and at roughly 90 degrees to the tip of the control arm, allows you to sweep the tip of the lower control arm front to back by sliding the rear bolt side to side. This gives you control of the caster without shims and cams and stuff like that. Not a great sytem but simple with very few parts, in a word cost savings.

The sad thing is that after a few pages of writing it still isn't that simple.

Alot of handling has to do with feel and feed back, it is subjective, if the STB gives you more predicability and feel you will have the confidence to drive faster than you did before. If it doesn't then even if the mechanical grip is improved, you will never use it, because it doesn't feel right.

I like the way my car feel now, but I made so many changes I don't know what was the best bang for the buck. I have seen alot of posts that say sway bars and shocks first, I think that is correct. They will have the largest effect and you know you have to have them.

The (STB) shock tower brace should be one of the later mods after shocks and sway bars. Sphon has a new adjustable one, with a turnbuckle in the center, that would be my pick. I think it would be much easier to install no need to egg out the holes like I had to do on the SLP.

Well thats is all I know or can guess on STB's, remember it is never as simple as it seems.

Severous01

hey, whatever the other numbers mean and represent mean nothing to the ones before the $ sign. all i know is before i got the stb i was spending $60 (notice the $) in front end allignments and checksevery 2 months, afterwards i spend maybe $60 per year. the stiffness of the front end for my car has changed dramatically. i wont deny i do have other parts as well, hal shocks and subframes, but what helped me save money on allignments was the stb. and i know it was this because it was the last thing i put on.

so all you geometry guys out there can keep truckin along and all you that think you can do without, do without. My car is better off with it in turns and with tires. thats my $.02 (there it is again, you cant get away from it)

mitchntx

I've been thinking a lot obout this ... more than I have prior. I appreciate your knowledge of physics. I wish I had taken some while in school. It would probably help me quite a bit to understand things more.

100% agree .. can't argue at all with that. Without loading, the STB installed or not installed has no affect.

When you turn the wheel, you will begin to slow down. Speed will scrub.

Consequently, the forces are sent rearward are now loading the rear mounting point of the A-Arm more than the front.

At 100% side loading, the force on the lower A-Arm was split 50/50 between the front and rear mounting point of the Lower A-Arm, agreed? As the wheel turns, the angle of the force then transfers more to the rear mounting point, agreed?

Because the knuckle is attached 6 inches away from the actual mounting point of the upper suspension, this would twist the upper mount, instead of loading it laterally, agreed?

Using your example figures, of 450lbs and then cut by 30%, yeilds 315lbs.

So, now with 315lbs of lateral loading, further cut because of the twist induced by the upper A-Arm's offset mounting point, the amount of lateral loading is getting quite small, don't you think?

Like I said earlier, I've had no formal training in physics. I'm a visual person and can visualize these loads and movements in my head. But, there is lots of room for error ...

I appreciate the effort you are putting into this. I am learning a lot ...

Z28barnett

That is a given.


Not exactly, when you turn you go from one type of velocity (Linear) to two types. (Linear-in a line) and (Angular-around a cricle). Turn the wheel and watch the speedo nothing changes. You get thrown to the side when you turn, not forward, that is due to the change in angular velocity. So you may feel that the forward motion is slowed and it has but unless you have appiled the brakes you haven't lost any energy. Unless the tires are skidding and sending up lots of smoke. In a cure you are now going two directions instead of one.

Because the lower arm is attched to a different structure and at least 2' away from the upper a-arm very little of what it does effects the upper a-arm. As long as you can assume that it is attached, you can ignore it.

Perhaps, but who cares? We are looking at the upper arm and shock tower.

The attachment is in a horizontal plane about 6" from the shock mount but in a vertical plane perhaps 1 1/2". The arm has bushings so it will not take a twisting load along the center of the bushing axis. You can only twist it perpendicual to the bushing axis and push and pull it perpendicular to the bushing axis.

Those loads were an simplified case. If you are under braking in a turn you could shift all of the weight to the front outside tire, even some of the rear weight. So loads will be much higher and not equal from side to side.

I see no evidence that you can make a solid case for no real loads in the shock towers. I see evidence of real loads in that area and hints of extremely high peak loads under special cases. Since you are trying to hold 1/2 a degree as a tolerance, it would be easy for a small amount of flexing to distub your aligment in a corner and that would give you a bad feeling in the steering.

The previous post about $$$$ analysis of the impact of the STB is interesting and a way to look at the situation. It is clear that he benifited from the brace, but I don't see how. None of the aligment adjustments are anywhere near the thop of the shock tower, all adjustments are on the lower control arms. If his shock bolts were loose and tightened after the install of the STB, that might explain it. I think it is great that it worked for him, but I don't see a reason that it did.

Any aligment changes I am talking about would only happen under load and the aligment would go right back to normal after you quit turning.

I have a B.S.M.E., but as the physical world loves to show you, you don't know everything. I once read a quip about the laws of physics, " Don't worry about the laws of phiysics, they will come and find you!!!".

Z28

mitchntx

When you turn the wheel, you most certainly bleed off energy. One is sliding the tire sideways, to a degree. Does it boil in smoke? No ... but unless you add energy to maintain, speed will decrease if the amount of energy fed stays constant.

If the bushing deflects, isn't that the same affect to the knuckle as if the mount twisted?

And if the bushing deflects, wouldn't it give way before the stamped metal piece the upper mount is attached to?

And if all the weight is shifted forward and to one wheel, would all the other tires have to be off the ground? I can lift an inside front on a hard turn, but I don't think I've ever done a stoppie in my Trans AM ...

Like I said, I'm a visual person ...
The more I think about the geometry up front, the more I realize I need to learn.

Saying an STB does NOTHING was over the top ... you've convinced me. There are subtle things going on when the car is under max loading of the front suspension. However, I can run Motorsports Ranch in my car, turning 1:28s, and I see no change in tire temps or tire pressures with or without the STB attached. Now that is real world data, not a feeling in my butt.

2 things are possible ... the STB has no affect or I'm leaving a LOT of car on the track.

So I will revise my opinion ... what good an STB does is almost impossible to quantify in the real world.

Good information ... I appreciate the time you have been taking ... everyone has an opinion. Challenging an opinion is a good thing, if one has the facts to back it up.

pHEnomIC

Thanks for the awesome info all of you. You are a little above my head but this is the most in depth response ive gotten from any posts so far. I guess the difference is very small but much of what we do to our cars do little things that all add up. Im probably going to get some subframes first and if i see any good deals i may get an STB.

Z28barnett

There will be some loss of energy to tire wear and heat, but not enough to create massive forces.

Yes I think it would be the same effect.

At first the rubber will give, but it will be progessively harder to deflect it. The psi that the rubber reaches over the large area in the bushing could withstand more force than the arm could take. The stiffest part will always take the load, the more flexiable stuff will move out of the way.

A real world test is important, an STB may not make enough difference to be important. That may be what your track times are telling us.

You might have to go to stiffer upper arms to see any change. I went to 1LE uppers/lowers and for the street that is getting pretty stiff, as much as I would do to a street car.

I did shocks, 1LE springs, sfc, STB, 1LE LCA all around, all at once so I can't tell what made the bigest difference. I would like to get the car to a track someday and see what it can do. But I am sure I am a better engineer than driver, and sometimes i wonder about the engineer part.

Without testing I can't say that STB will do any good, but in theory it might have an effect. So it is better than fuel line magnets and spinning exhaust widgets. I think that you will agree that an STB, is always better than a STD.

Nice chating with everyone I hope I have given out some food for thought. But the old gray matter is wrung out. I don't have anything left to add.

Z28

"White Knight"

Well you could make something and check........I am sure they have something out there that you can mount in place of a STB and it has some kind of way to measure the load on it. I would assume it could be made....how..i have no idea. But some company should make it and try it and lay this issue to rest.

YZF/LS1 Freak

I know that a STB does not do A LOT but I plan to pull my front sway bar and I have rear a few posts were guys pulled the bar and the car was a little looser and when they put the STB on it felt normal again, AND it looks cool and cars shows and stuff.

Now, someone PLEASE explain to me the point of an adjustabe STB!

km9v

WOW! This thread has gotten technical to the nth degree. Are any of you mechancial engineers or physists???? In my opinion, a STB is designed to reduce front end / K - member flex while turning. There are some really interesting arguments here, but regardless of load shifting & what not, I think we can all agree that a STB will reduce front end / K - member flexing.

My $.02

Z28barnett

Yes, I am, got a job open? I don't want to relocate to India.

These posts show that everyone doesn't agree with the STB is good conclusion. I bought one, so I am either a sucker or a smart shopper.

The k-member is so massive and so far from the top of the shock towers that a shock tower brace is unlikley to have any effect at all on its stiffness.

The flex in the shock towers themselves could be reduced by a STB. But the extent and importance of the bracing effect is open to debate without data.

The fact that an STB did not improve lap times for mitch is a concern. I would feel better about my STB if he had gotten better lap times with one.

The STB is a brace and could help, but a real world test showed no change, that should not be ignored. Tests trump theories, and leave the question open.

Z28

Z28barnett

It has a few purposes from my point of view.

1). You should be able to install it without any drama or hole grinding, unlike my SLP 2-pt.

2). Since it can be adjusted to fit your car the holes will be a better fit and it will take a tension or compression load quicker. It can also be tightened to preload the bar. Years ago I looked at an Mita "R" model with Bilstein shocks and a STB, sure enough the factory made the bar adjustable. It was a turnbuckle system just like Spohn has.

Z28

TobyZ28

Thought i would dig up this great old post. Just want to post a link to my feedback on putting an STB in my vert.

https://www.camaroz28.com/forums/sho...d.php?t=609360

For me there was a VERY noticable differance in very (very) hard cornering and maintaining control in a turn when you're driving it to or just beyond the limits of the car.

I think it may be a combination of my car A) not having SFC's in yet B) being a Vert C) Stiffer 1" lowered springs. D) Knowing my car really really well