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Suspension nerds! Will this make my swaybar stiffer...


turbogrill
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Hi,

 

Would adding a spacer like in the middle picture make the swaybar stiffer? I think most people agree that the right picture will make it stiffer but there is some confusion about the middle picture.

- The swaybar is 90 degrees to the control arm (like in the photo)

- The swaybar moves down and up in the picture

- The green line is the endlink

- The red box is the swaybar (goes outwards from the screen 90 degrees from control arm)

- Black is the control arm

- Gray is a spacer made out of super duper material with zero flex.

 

The question is if the middle picture will change the motion ratio...I am hearing different things from different people. Some say it's the attachment to the control arm that matters and middle picture does nothing. 

 

(There was a different thread that ended up talking about this but it was a bit OT)

 

bla2.thumb.jpg.07894caa7acc5a32dda0324a3747ca87.jpg

Adjustable Sway Bar Endlinks Mazda Miata MX-5/RX-8 FE (NC)

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Exactly.

 

This is a common misconception with a lot of suspension parts.

 

Think of it like this...

 

Imagine anywhere that you have a link for suspension (control arm, tie rod, swaybar link).  This link is ALWAYS going to act like a straight line between the end points.

 

Does not matter if it takes a squiggly line between the 2 points, the end result is going to act as a straight member between the two points (if we ignore stiffness of the actual link itself).

 

In other words, the middle is exactly the same as the left.

Edited by wvumtnbkr
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24 minutes ago, ablesnead said:

there is no super duper...only flex , even if only the connections......so ultimately the middle would be softer, a smidge

 

7 minutes ago, SonsOfIrony said:

Such an increase in link length will just end up twisting the end of the bar or breaking things.

 

Not to mention it adds unsprung weight.

Clearly missed the point 

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If the spacer in the middle picture stays parallel to the lower control arm (no flex), it is effectively the same as mounting the end point to the control arm in the right picture.

 

The point to remember is how much the lower link from the sway bar (and hence the end of the sway bar) moves in relation to the wheel. That's the motion ratio. Then you square that to find out the effective wheel rate for a given spring or sway bar rate.

 

If you lose 10% of that travel to flex, that can be calculated to come up with the true or actual motion ratio. Again, the motion ratio is the amount of travel at the end of the sway bar (or spring) divided by the amount of wheel travel. 

Edited by mender
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8 minutes ago, mender said:

If the spacer in the middle picture stays parallel to the lower control arm (no flex), it is effectively the same as mounting the end point to the control arm in the right picture.

 

The point to remember is how much the lower link from the sway bar (and hence the end of the sway bar) moves in relation to the wheel. That's the motion ratio. Then you square that to find out the effective wheel rate for a given spring or sway bar rate.

 

If you lose 10% of that travel to flex, that can be calculated to come up with the true motion ratio. Again, the motion ratio is the amount of travel at the end of the sway bar (or spring) divided by the amount of wheel travel. The linkages in between only affect that through flex/deflection.

 

This is the other argument! Seems to be the same two divided opinions in the Miata forum as well.....:)

 

 

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20 hours ago, turbogrill said:

 

This is the other argument! Seems to be the same two divided opinions in the Miata forum as well.....:)

 

 

Think about it: the sway bar end moves a certain amount, and the wheel moves a certain amount. That's all that matters.

 

Spade/blade type sway bar adjusters change the roll stiffness by adding or taking away flex between the sway bar and the wheel. That changes how much the end of the sway bar moves as compared to the wheel. Simple once that is understood. 

 

Which Miata forum? :)

 

Edit: found it. Jim's right, v67gsr is wrong. ;)

 

In post #10, v67gsr is also wrong about the spacer between the lower coilover mount and the spindle; removing that spacer would tilt the coilover away from vertical and would reduce the effective wheel rate, not increase it.  Not to mention reducing spring to tire clearance. I'll let you tell him.

Edited by mender
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For anyone who is still struggling with this, imagine a picture between the middle one and the one on the right. Add a bracket directly under the outer end of the spacer. That in real life would keep the spacer from flexing. It wouldn't change what's happening with the outer end of the spacer.

 

At this point, one could leave the spacer in place but it would only add weight. Remove it and you have the picture on the right with no change in how things are working.

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19 hours ago, turbogrill said:

Hi,

 

Would adding a spacer like in the middle picture make the swaybar stiffer? I think most people agree that the right picture will make it stiffer but there is some confusion about the middle picture.

- The swaybar is 90 degrees to the control arm (like in the photo)

- The swaybar moves down and up in the picture

- The green line is the endlink

- The red box is the swaybar (goes outwards from the screen 90 degrees from control arm)

- Black is the control arm

- Gray is a spacer made out of super duper material with zero flex.

 

The question is if the middle picture will change the motion ratio...I am hearing different things from different people. Some say it's the attachment to the control arm that matters and middle picture does nothing. 

 

(There was a different thread that ended up talking about this but it was a bit OT)

 

bla2.thumb.jpg.07894caa7acc5a32dda0324a3747ca87.jpg

Adjustable Sway Bar Endlinks Mazda Miata MX-5/RX-8 FE (NC)

no idea but that looks awful cheaty as it is... 

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3 hours ago, turbogrill said:

Great explanation. I should add a new picture.

If there are still any dissenters at this point. :)

 

Just thought of something: you might want to make it clear that the green link has pivots at either end and that the spacer to control arm mount does not (rigid).

Edited by mender
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So, after a bit more thought, the easiest way to get a jump in effective wheel rate in this pictured suspension would be to flip the lower heim joint to the other side of the bracket (toward the wheel), add a 1/2" spacer at the upper heim to move that outward as well, and then make the links longer.

 

The upper spacer and longer links are to reduce the loss of effectiveness due to angularity. Keeping the link within 15 degrees of vertical plus the lower heim joint move should get you about a 30% increase in effective sway bar rate.

 

I figured I'd better correct this: actual roll stiffness is a combination of springs and sway bar. The amount each one adds to the overall roll rate depends on the combo. A 30% sway bar change might be enough to tune the handling once it's close, but not enough if you have a severe push. To put it in perspective, a 30% sway bar rate change is the same as going from a 15/16" bar to a 1" bar; usable but not a huge step, especially if the car has very stiff springs. Just to be clear.

Edited by mender
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The easy money would be mounting the lower link joint 180 out (ball of joint facing outward) and bending the swaybar arm to meet it. Since this would move both the lower and upper pivot outboard about an inch, the motion ratio would change (most likely a really small amount). 

Edited by Black Magic
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26 minutes ago, turbogrill said:

 

Sorry it's a secret. Luckily chumpcar hasn't banned it (like carbon fiber). 

 

The green indicated sarcasm as the material you think you have doesn't exist.

 

IF we assume this wundermaterial is infinitely rigid, which it isn't, then scenario 2 and 3 are the same. 

 

Why not drill holes in the ARB closer to the mounting points to increase the effective stiffness? Your solutions add unsprung weight and introduce a ton of bending loads that will cause failures.

 

EDIT: I saw you in the previous thread. If your plan is to only move the attachment point a small distance, say 1 in, then a small spacer and longer bolt wont cause too much of an issue. I was a bit taken aback by the "not to scale" nature of your illustrations.

 

I like the Idea of mounting to the lower shock mount by a hanging end link. You may be pushing that cantilevered bolt, however.

Edited by KoneKillah
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On 3/28/2020 at 10:07 AM, mender said:

If there are still any dissenters at this point. :)

 

Just thought of something: you might want to make it clear that the green link has pivots at either end and that the spacer to control arm mount does not (rigid).

 

Here here! Middle is effectively the same as the right picture IF we assume infinitely rigid spacers.

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40 minutes ago, KoneKillah said:

 

Here here! Middle is effectively the same as the right picture IF we assume infinitely rigid spacers.

Pretty sure he was only trying to establish the effect of moving the heim joint (pivot), and as such in a thought experiment went to the extreme to get to the crux.  :)

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5 hours ago, KoneKillah said:

 

The green indicated sarcasm as the material you think you have doesn't exist.

 

IF we assume this wundermaterial is infinitely rigid, which it isn't, then scenario 2 and 3 are the same. 

 

Why not drill holes in the ARB closer to the mounting points to increase the effective stiffness? Your solutions add unsprung weight and introduce a ton of bending loads that will cause failures.

 

EDIT: I saw you in the previous thread. If your plan is to only move the attachment point a small distance, say 1 in, then a small spacer and longer bolt wont cause too much of an issue. I was a bit taken aback by the "not to scale" nature of your illustrations.

 

I like the Idea of mounting to the lower shock mount by a hanging end link. You may be pushing that cantilevered bolt, however.

 

Yes I know the material doesn't exist (or does it...).  To simplify the discussion I wanted to assume some things ideal.

 

Drilling the swaybar is also an option!

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1 hour ago, turbogrill said:

 

Yes I know the material doesn't exist (or does it...).  To simplify the discussion I wanted to assume some things ideal.

 

Drilling the swaybar is also an option!

 

It's the best option IMO. If you do go that route make sure to weld in a lug so the through bolt doesn't get damaged over time.

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