DamonB

We know the stock FD front sway bar mounts are a weakness and aftermarket ones fix that problem. I have been looking into assembling some new pieces in order to build a new front sway bar and got to thinking about the stock mounts.

First off, I don't feel that Mazda engineers are the idiots that some people do. So why do the stock mounts hang down so low? Because they have to. If the front sway bar is mounted higher in the chassis then when the suspension is at rest the arms of the sway bar are not parallel to the ground (the only exception would be a much lowered car). Keeping the arms parallel to the ground is important for a couple reasons. First, it decreases the load on the sway bar mounts and endlinks. Second, it results in the load of the sway bar being more linear with suspension movement.

Picture the sway bar from the left or right side with the arms parallel to the ground (stock). As the car rolls, one side twists up and the other down; the forces balance very nicely and the sway bar mounts for the most part merely see the torque around the bar. Now picture the sway bar on raised aftermarket mounts. Since the bar is higher the front of the sway bar arms are now higher than the rear and not parallel to the ground. As the car rolls the lever geometry of the arms is now trying to push the bar out the front end of the car, putting a much higher strain on both the sway bar mounts and the endlinks. Also, since the sway bar arms are not parallel to the ground at rest, as the car rolls one arm will pass "over center" and so the roll resistance of the bar will no longer be linear. The rate will rise until one arm passes through the horizontal and then the rate will still continue to rise, but at a lower rate. This is because of the lever action of the arms. This idea is tremendously simpler to show with a drawing and I will work on that.

My idea is to go ahead and raise the sway bar using aftermarket mounts, but ditch the stock Tripoint arms. In order to keep the arms parallel to the ground and also allow the bar to be mounted higher in the chassis, the arm must be bent when viewed from the side, like below.



Also, I have found I had misunderstood an idea I had elsewhere. The Tripoint bar for instance has 5 holes in the arms which allows 5 different settings. I experimented at one time with "half" settings by putting one endlink on hole 4 and one on hole 3 for example. This works fine for creating my goal of having a roll rate halfway between those two, but it has a discrepency. When the car is flat and goes into dive under braking the bar will twist slightly and actually add spring rate to the front end! Since the lever arm is different at each side with the end links attached in different places you can see that if you raise both suspension arms the same amount the bar must twist. Is that good or bad? I think overall it would be bad, but for the hell of it I am going to sit down and actually figure out how much rate it adds. It may not be enough to be concerned with.

reza

Would the end link compesates for these movement you describe when we use highes swaybar mount.

DamonB

Nope, because the endlink can't get short enough; the bottom of the suspension arm would still be too far below the bar. Short as possible endlinks would be a compromise though.

artowar

iTrader: (1)

I think that I understand your point, but I don't see how the bent arm will solve the issue. It seems to me that you would arrive at the same rate througout the motion of the bar/arm/link combo by using straight arms and lengthening the end links so that the arms are a bit lower in back (rather than level).

It also seems to me that if you really wanted a linear rate, then assuming that the bar itself maintains a linear rate throughout its range of twist, you would need to keep the force acting on the arm at a tangent to the circle described by the center point of the bar and the center point of the pivot at the end of the arm (i.e., where the link attaches).

Now, how you would accomplish that, I have no idea. Perhaps that is one of the reasons that certain racing suspensions use other types of roll control devices.

reza

I think end link needs to be longer to compensate the arm movement.
If its too short then there are not much play.

With more length, you can have the end link move away from the arm. Similar to your arm movement, human arm, i mean your upper arm and lower arm. With your upper arm attached if you push in your lower arm, your elbow has to bend and the upper arm move to compensates

Not sure if I got the idea right...

Reza

DamonB

The bent arm allows it to stay parallel to the ground while raising the sway bar tube higher into the chassis at the same time.


I agree with you here. My use of "linear" is incorrect in it's truest sense, but I was trying to describe how the rates would differ due to the fact that the moment arm length changes as the arm describes an arc in its movement.

DamonB

I think you are trying to say that short endlinks may bind as the suspension travels through large degrees of rotation? Having endlinks as long as possible is good in a geometry sense because the position of force input into the sway bar arm will always be closer to perpendicular. That would always be good, but not at the expense of having the sway bar arm no longer parallel to the ground as it would be in an FD.

Picture the sway bar arm angled down towards the rear of the car at (a very extreme case) 45 degrees. The endlinks acting on that arm are nearly vertical, so when they act on the arm there is a very large force pulling horizontally towards the front of the car. This just stresses the endlinks (they can handle it) and the sway bar mounts much more. Since the sway bar mounts drop so far from the chassis that leaves quite a long lever arm to bend the mount or deform the chassis at the point of connection.

jimlab

Damon, which sway bar mounts do you have? I stupidly sold my "FTL" (Trev Dagley) sway bar mounts which were built like the proverbial "brick shithouse", but I now have a set of the Crooked Willow billet mounts David Breslau made for me specially. I haven't installed them yet, but have heard/read that they raise the sway bar mounting points for more ground clearance, which must be what you're talking about?

KevinK2

From DamonB

"My idea is to go ahead and raise the sway bar using aftermarket mounts, but ditch the stock Tripoint arms. In order to keep the arms parallel to the ground and also allow the bar to be mounted higher in the chassis, the arm must be bent when viewed from the side, like below."

This gains nothing, excpt cosmetics. For a high bar, with low and vertical endlinks, it matters not whether the trailing arms are strait or bent to be parallel with the road at the link end. The performance is exactly the same, base on the pivot axis of the transverse bar, and the pinned connection to the vertical link, at the bar end.

From DamonB

"Picture the sway bar arm angled down towards the rear of the car at (a very extreme case) 45 degrees. The endlinks acting on that arm are nearly vertical, so when they act on the arm there is a very large force pulling horizontally towards the front of the car. This just stresses the endlinks (they can handle it) and the sway bar mounts much more"

Not true. The for/aft thrust will be proportional to the for/aft inclination of the vertical link. If near vertical, then no for/aft thrust to sbar support. A link with 2 pinned connections at the ends can only carry force through the pin centers. Trouble starts with extreme settings on the front tripoint bar.

I prefer to have the rear bar adjustments, where forces are much smaller. I modified the brackets there so the main bar pivot axis can be moved forward for the short bar setting, keeping the link near vertical.

I do agree things get funky with half settings. I concluded roll stiffness of the bar is at the mid setting. But, compared to a balanced setting on both arms, the front end will drop more when cornering in one direction, and raise more when doing an opposit corner.

As you note, front will stiffen when braking as bar twists, but it also results in uneven L-R tire loading, which could be twitchy.

DamonB

I don't disagree that the sway bar still works as intended, but if the arms are not parallel to the ground then the load from the endlinks fed into the sway bar has a large resultant force towards the front of the car which stresses the mounts fore and aft.


The majority of the load in the system is actually in the torque tube of the bar. The farther from perpendicular the input of the force through the endlink/arm then the more fore/aft thrust will go through the torque tube and it's mounts. The endlink may remain vertical, but if the arm is not horizontal there is still a resultant force fore and aft. That's a given if you draw a simple force vector diagram of the system.


I have no experience with fiddling with the rear bar as by rule I must leave it stock. I can say that on race rubber I can run fearsome amounts of roll resistance in the front and the car is neutral on road courses (that I guess illustrates thaT Mazda made the right choice in softening the rear bar on later models). On (slower) autox courses I can't run as much front roll stiffness because the lower speeds don't give me as much weight transfer.

I disagree. The bar is still fine in cornering. The reason is that the torque tube is affixed at its ends via the arms to the suspension. If one arm were 6" long and one were 12" long it makes no difference in cornering. All the torque tube knows is that is gets twisted. During roll that it twists more from one side then the other makes no difference at all to it. The overall torque through the tube is still the same. In fact many racecars adjust roll stiffness by leaving only one side of the sway bar adjustable with a sort of sliding endlink. This is not perfect because of the chassis dive issue as I found, but it certainly does change the roll stiffness and does not make the bar stiffer in one direction than the other.

As an exmaple take the bar from the car. Grip one arm at it's end and the other at its middle. Twist one way. Twist the other way. Now swap the positions of your hands. Twist one way, then the other. You'll find it takes the same amount of force to twist in each case. The longer lever arm on one side is offset by the shorter one on the other side. It still balances out.


True, but I am going to compute how much. As in my sliding endlink example above, I know many racecars do in fact use this system so it must not be a terrible amount of force.

I disagree as I feel my example about twisting the bar in your hands is sound.

DamonB

Reinforced stock type from Mazda Motorsports. They are the same height as stock but made from solid tube rather than welded up plates.

Yes. The point I am trying to make is that the geometry is more favorable with the bar mounted in it's stock postition; that's the reason Mazda put it there.

KevinK2

DamonB,

You need to understand the principal of structural links with pinned ends ... ie ball pivots at ea end. Loke truss links in a ME bridge statics problem. At the end attachments, no moment can be transfered, and the link can only carry a force vector passing through both end pivots. In your example, with vertical links, there is no for aft reaction in the arms, just a vertical force applied at the link joint. It's not intuitively obvious. Imagine links removed, and bar ends angled down at 45 deg. now tie 4" string to each bar end .... pull one string up, the other down. Torque is applied to sbar w/o for aft forces.

for unequal arm lengths, the forces at the short arm will be higher, for consistent torque along the bar midspan. my analysis, looking at roll stiffness and vertical support loads at the springs, showed the cornering behavior I noted. When braking in a strait line, this will also result in unbalanced vertical reactions at the frame where the main pivots are, thus rotating the body, resulting in unbalanced side to side tire loads. For short arm at RF, net vertical force to front frame increases (less dive), body rolls left, tire force bias will be on RF and LR. The effect could be small, but it is there.

I do this stuff daily, often with FEA, as an ME consultant, fwiw.

DamonB

Alright, you've changed my mind.

I still don't understand how the force at the pivots would be unbalanced. The reaction force at the arms may seem different if the arm lengths are unequal, but that reaction force only acts via the opposite endlink through the torque tube. The torque tube will be equally stressed about it's entire length in any case; it can't twist more at one end then the other. How then can the mounts not be equally stressed?

KevinK2

As you said, the torque is constant along the straight part of the bar. The link and pivot at ea end define the moment arm to resist the torque. Since arm is longer at one end, that end will have smaller, equal forces at the link and pivot (force couple) to resist the main torque. The short arm has higher reaction forces to the torque.

Your initial instinct is correct ... having the pivots and the lower link joints in the same horizontal plane that's parallel to the ground, with vertical links, is a good thing. It will minimize the link angles that occur during compression and extension of the suspension, and thus minimise the bad for/aft (and side to side) thrust forces that help crack mounts and frames.

DamonB

I've devoted some more thought to this and realize my original ideas about loads in the mounts may be incorrect but fact is when the car is at ride height you want the sway bar ends parallel to the ground. More specifically you want the arms of the sway bar to be perpendicular to the rods on the suspension that actuate it. The reason is that this gives the lowest and most linear ratio of bar twist vs suspension movement. If your arms are no longer parallel to the ground you have just softened your sway bar because as the suspension moves you are now feeding fewer degrees of rotation into the torsion bar. This effectively means the rate of the sway bar is less than if the arms were parallel to the ground. At the same time as the arms rotate from horizontal the length of the lever arm changes slightly. If the arms are not parallel to the ground at static ride height then the effective rate at the bar is not going to be linear or increasing with suspension travel, it will actually be a decreasing rate.

If the car is lowered the suspension arms are positioned higher in the chassis and thus you could raise the sway bar the same amount without changing the arm angle. If you were also to use shorter drop links between the sway bar and suspension you could raise the bar while keep the arms horizontal. You could also use cranked arms as in the pic in my first post.

I'm currently mocking up my own bar mounts since I refuse to pay $200 for tubular steel ones from Mazda Motorsports and at the same time I'm changing the bottoms so the solid bushings of my Tripoint will bolt on without the use of the extra Tripoint braces. I'm also working on making parts to allow me to use the shortest drop links possible so I can raise the mounts while keeping the arms parallel to the ground but the shorter links are going to give me problems since my bar is adjustable. At this point I'm unwilling to spend the dollars on fabbing cranked sway bar arms but they would be the best solution for my adjustable bar in allowing it to mount higher in the chassis. If the bar arms aren't roughly parallel to the bottoms of the suspension arms it will make it more difficult for the adjustable drop links to bolt up correctly at the various holes in the arms.

KevinK2

"I've devoted some more thought to this and realize my original ideas about loads in the mounts may be incorrect but fact is when the car is at ride height you want the sway bar ends parallel to the ground. More specifically you want the arms of the sway bar to be perpendicular to the rods on the suspension that actuate it. The reason is that this gives the lowest and most linear ratio of bar twist vs suspension movement. If your arms are no longer parallel to the ground you have just softened your sway bar because as the suspension moves you are now feeding fewer degrees of rotation into the torsion bar. This effectively means the rate of the sway bar is less than if the arms were parallel to the ground. At the same time as the arms rotate from horizontal the length of the lever arm changes slightly. If the arms are not parallel to the ground at static ride height then the effective rate at the bar is not going to be linear or increasing with suspension travel, it will actually be a decreasing rate."

"Arms parallel to ground" means little unless you mean straight arms comming off the cross tube, like TP .... that defines the postion of a kinematic link with 2 ends.

If that is the "parallel" your talkin about, then you are consistent with what I said at the end of my last post.

"More specifically you want the arms of the sway bar to be perpendicular to the rods on the suspension that actuate it."

What rods ... the bar end links or are you talkin lower control arm?

DamonB

The drop links that connect the sway bar arms to the suspension arm. The most ideal attachment would be for the drop link to be vertical and attach perpendicularly to the sway bar arm (assuming the suspension arm the drop link attaches to is horizontal with no anti-dive or squat, otherwise you'd want the drop link perpendicular to the axis the suspension pivots on). This ensures the most constant motion ratio of suspension movement vs degrees of bar twist and in my mind explains why every car (street or race) I've ever seen that wasn't severely monkeyed with takes care to keep the bar arms parallel to the road.

I think that's another reason a blade adjustable bar is so ideal. Your motion ratios stay constant no matter what the setting of stiffness of the bar since the joints are of a fixed length. Only way to do that with a "regular" sway bar is to change the torque tube for various amount of stiffness rather than adjusting the lever arm of the bar.

I wish I knew how to make a simple animation to show how the motion ratio of a sway bar with a lot of tilt to the arms changes more drastically through the range of suspension movement versus a bar with horizontal arms.

KevinK2

Ok, that's basically what I had said. Just that parallel can be misleading. If a bar end snakes about with no strait length, main issue is the bar pivot centers and the lower end link centers are in same horiz plane, ~parallel to ground, and the endlinks are vertical. This results in minimal lateral loads at the pivots. This is how the stock FD set-up is.

For FD, true upper end of vert link is high on the control arm. A lowered FD would put it much higher than the lower control arm pivots. So although set up as noted, the vertical end link force would have a reduced component rotating the control arm, and a component that tends to pull or push against the control atm pivots. Still quite linear, for control arm rotation vs bar reaction force, but a little bit softer. No big deal.

I did design a rear bar for another car (design by analysis, not to be confused with CAD design by shape ...) It was similar to the TP front, except the support bracket for the custom split aluminum pivot blocks had similar multiple mounting holes, so the end link was always vertical.

Not sure of SS rules, but a support that integrates the TP brace may allow multiple bar for-aft positions.

On my FD, I took a die grinder to the rear eibach pivot blocks, and used socket head cap screws, and some special washers, to create pivot blocks with an offset center. I can keep the links vertical, at the stiff or soft bar holes.

DamonB

I know my descriptions are confusing and I've tried to limit it just to the FD to make it simpler but I think most people don't get what I'm trying to say. Some sort of animation would make it obvious but I don't have the resources to do that.

In SS you can do whatever you want with the sway bar mounts as long as they are not braced to eachother. That means you can build new mounts and even brace each mount individually to the chassis which is what the Tripoint braces do (but can't use something like the Racing Beat brace that ties the mounts together). The Tripoint solid bushings have slots in them and allow you to move the bar for and aft slightly to help with the geometry.

I'm currently building new sway bar mounts for my car. Basically the geometry is the same as stock but the lower mounting pad for the bar is completely different so I can bolt the big Tripoint solid bushings on directly without using the extra braces. The solid bushings are too big to fasten on any mount without use of the Tripoint braces that extend back from the mount to two unused holes on the subframe.

I'm hoping to prevent something like this again. The bearings at the top should be flat on the bottom and the braces in the middle should not look like pretzels I still can't believe that I bent the arms and ruptured the drop links too!

KevinK2

The TP bearings are std mcmaster carr parts ... 7930K18, $17 ea. They have a very long base at 6", and 4.56" hole span. Hardare could be mod'd for more compact design. Mcmaster also has a 1.25" UHMWPE bush ***'y that is self aligning, 4.56" long, and 3.25" hole span. .06" taller. 6252K73, same price.

The more compact standard TP bearing block will work as well, if carefully installed. I have zero bind, free play, or squeaks on my eibach.

Compact pivots would allow a few fore-aft positions, as I described before.

The TP arms should be mod'd for socket head cap scews, that are near flush with the arm bottom surface.

Arms that slope down slightly will not create a large force error, and would justify a higher bar for more clearance.

Are you at stock ride height for SS?

DamonB

Yes.

Thanks for the McMaster parts numbers as I've run across them before but haven't verified if they were in fact the same as the Tripoint parts. Have you used them? I know for instance that I bought new generic locking collars for centering the bar and had to mill a few thou out of the center to make them slip on easily. I was worried I'd have the same issue with the bearings.

I considered making plain aluminum mounting blocks for the bar but I think it's easier to just stick with something steel since I'm having the parts laser cut and milling the aluminum would be much more expensive.

I though about counterboring the pinch bolts on the arms a while back but decided against it. I would rather scrape the bolts than the arms and with my daily driver I do drag the bolt heads on occasion even trying to be careful. I keep a few spares in my "quick swaybar adjust kit" in the toolbox.

M104-AMG

iTrader: (8)

I'm thinking about getting the Tripoint front swaybar, however, this thread has me second-guessing TP's engineering.

Perhaps I would be better off just purchasing their splined torque tube, and waiting for DamonB to offer better arms and matching swaybar mounts for higher clearance and less susceptibility to damage.

DamonB: will you be offerring any of these ?

Thanks,
:-) neil

DamonB

There's no free lunch when you try to daily drive a "race" car. There is absolutely nothing wrong with the Tripoint hardware; it's top notch stuff. I finally built my own mounts recently because what I really wanted was not available and I refuse to pay $200 for aftermarket mounts that use about $30 worth of material. I just had enough steel laser cut to build three sets of mounts and I spend barely $100. Granted I had to weld them up but now I've got something I really wanted.

I'm still considering making my own arms from commonly available parts but if the new mounts work out well (which they are) there's no sense in me going to the trouble.

t-von

iTrader: (8)

I was looking underneith my Fd today and noticed that the passenger side sway bar mount was completely broken(no wonder the car's been feeling kinda funny). While down there, I did notice that the arms of the sway bar are level to the ground. If the aftermarket mounts are shorter, why not just lower the vehicle w/coilovers or shocks to make up for the differance? If that isn't enough, couldn't you just fab some spacers to the sway bar mounting surface to lower the aftermarket mounts so things level up again? In the end, all we really care about is them being stronger right?

DamonB

You're correct, that will accomplish the same thing.

You could but it would demand you use very long bolts to go through the mount and spacer and into the chassis. This could contribute to bending and/or fretting between the mount, spacer and chassis.