My take on Lower control arm brace

[Will F.]

The deflection between braking & acceleration is pretty eye opening:

Although it is true there is deflection both ways its still far worse backwards. Your video is prof of this. The arm looks almost twisted while applying the brakes. Still this singular arm is going to control the arm from deflecting for and aft just from the way it is attached to the control arm.

[Gruffalo]

Wow, that video is an eye opener! Where will you attach the brace ? To the frame? And how will you achieve a straight line of suspension travel, the brace being a radius arm (in effect).

Definitely rooting for this one!


2015 VW e golf
2005 BMW 120i
1987 Porsche 928 S4
1981 Delorean dmc-12
1980 Fiat bertone X1/9

[Will F.]

[QUOTE=Gruffalo;223921]Wow, that video is an eye opener! Where will you attach the brace ? To the frame? And how will you achieve a straight line of suspension travel, the brace being a radius arm (in effect).

Definitely rooting for this one!


It will mount the same as all the other designs. From the rear control arm mounting bolt to the lower shock mount bolt. That way it utilizes factory mount points and makes reverting back to original very easily.

[dmcjohn]

Someone (in Germany I think?) used a similar design at one point - to use a solid tubular link between the back of the front lower control arm and the frame bolt. They went a step further and welded a bracket onto the frame to put the link in double shear at the frame. However, I believe they removed the brace again after testing.... I'll have to try and find that thread.

My only concern with making the lower control arm completely unable to deflect backwards by using a solid link like this (rather than the flexible one offered by Ed Uding), is that it would seem to me that you are introducing tension into the system.

The sway bar is mounted to the front frame extension and to each lower control arm. If you picture removing the lower control arm / spring / shock from the car, and just leaving the sway bar attached to the frame extension - as you lift it up and down it pivots on that frame extension mounting point, and the ends of the sway bar travel up and down in an arc, not in a vertical straight line.

Now put the suspension back in place, along with your solid link, which causes the lower control arm to travel straight up and down and does not allow any rearward deflection. The swaybar end is bolted to the lower control arm, which now prevents the sway bar from traveling in the arc - therefore there is now tension in the system as it goes through upward motion. So as the suspension compresses, and does not allow the sway bar to travel in an arc any longer, what is happening to the sway bar? Does the sway bar bend to mitigate (and over time will this cause metal fatigue)? Maybe the sway bar bushings are able to compress enough to take up the strain, without causing the sway bar to bend? I don't know, but I imagine this is why Ed's solution allows the braces to flex somewhat.

I'd love to see a solution which fully triangulates the lower control arm like what you are proposing here, so long as the movement of the sway bar is taken into account. On later mode Lotus Esprit's, I believe they added a very similar brace as what you are proposing, but (please correct me if I am wrong) they did this in conjunction with making a slide bushing on the end of the sway bar, so that it was able to still travel through it's natural arc while the lower control arm was prevented from deflecting backwards any longer. Maybe another solution would be a different sway bar mounting to the lower control arm using a drop link rather than a direct attachment.

Thanks,
John

[Josh]

Someone (in Germany I think?) used a similar design at one point - to use a solid tubular link between the back of the front lower control arm and the frame bolt. They went a step further and welded a bracket onto the frame to put the link in double shear at the frame. However, I believe they removed the brace again after testing.... I'll have to try and find that thread.

My only concern with making the lower control arm completely unable to deflect backwards by using a solid link like this (rather than the flexible one offered by Ed Uding), is that it would seem to me that you are introducing tension into the system.

The sway bar is mounted to the front frame extension and to each lower control arm. If you picture removing the lower control arm / spring / shock from the car, and just leaving the sway bar attached to the frame extension - as you lift it up and down it pivots on that frame extension mounting point, and the ends of the sway bar travel up and down in an arc, not in a vertical straight line.

Now put the suspension back in place, along with your solid link, which causes the lower control arm to travel straight up and down and does not allow any rearward deflection. The swaybar end is bolted to the lower control arm, which now prevents the sway bar from traveling in the arc - therefore there is now tension in the system as it goes through upward motion. So as the suspension compresses, and does not allow the sway bar to travel in an arc any longer, what is happening to the sway bar? Does the sway bar bend to mitigate (and over time will this cause metal fatigue)? Maybe the sway bar bushings are able to compress enough to take up the strain, without causing the sway bar to bend? I don't know, but I imagine this is why Ed's solution allows the braces to flex somewhat.

I'd love to see a solution which fully triangulates the lower control arm like what you are proposing here, so long as the movement of the sway bar is taken into account. On later mode Lotus Esprit's, I believe they added a very similar brace as what you are proposing, but (please correct me if I am wrong) they did this in conjunction with making a slide bushing on the end of the sway bar, so that it was able to still travel through it's natural arc while the lower control arm was prevented from deflecting backwards any longer. Maybe another solution would be a different sway bar mounting to the lower control arm using a drop link rather than a direct attachment.

Thanks,
John

Excellent information here. Thank you for contributing this John!

I have a project coming up this winter, which will use sway bar end links (like most cars) to get around this issue.

[Gruffalo]

Regarding tension... I understand John's point, but that tension must be negligible compared to the load on the sway bar when braking, as seen in the video.


2015 VW e golf
2005 BMW 120i
1987 Porsche 928 S4
1981 Delorean dmc-12
1980 Fiat bertone X1/9

[Lwanmtr]

Any energy from the suspension moving has to go somewhere, so as was mentioned earlier, the sway bar is designed to take the energy in a certain way, as is the frame...if you force that energy to move in a different direction it could cause stress in areas not designed for it. I'm not an engineer, but the frame and suspension parts were designed to work together in a specific way, altering that can cause problems. For certain you will need to make your mounting point on the frame more able to withstand basically the energy of the whole car pushing and pulling on it during braking and acceleration.

I hope you get working and that it works out fine....just giving my thoughts on doing a radical change like that.

[Patrick C]

Someone (in Germany I think?) used a similar design at one point - to use a solid tubular link between the back of the front lower control arm and the frame bolt. They went a step further and welded a bracket onto the frame to put the link in double shear at the frame. However, I believe they removed the brace again after testing.... I'll have to try and find that thread.

Ed Uding did this before switching to his more flexible braces. The frame was unable to handle the strain, as I recall.

As Ed said in this thread (please remember english is not his native language): http://dmctalk.org/showthread.php?68...l=1#post100689

It is not the same concept, your set is only the rear support that will stress the bold and frame in the end.
This is what we start with, after test and calculation it was not the way to go.
The force is a lot more thane you think, it is still a wonder that all the stock lower arms there.
Rust and bend metal , make it more weak thane it shoot be.
Call it what you like, as long you don,t call it Same concept.

Ed Uding
Delorean Europe

[Josh]

Any energy from the suspension moving has to go somewhere, so as was mentioned earlier, the sway bar is designed to take the energy in a certain way, as is the frame...if you force that energy to move in a different direction it could cause stress in areas not designed for it. I'm not an engineer, but the frame and suspension parts were designed to work together in a specific way, altering that can cause problems. For certain you will need to make your mounting point on the frame more able to withstand basically the energy of the whole car pushing and pulling on it during braking and acceleration.

I hope you get working and that it works out fine....just giving my thoughts on doing a radical change like that.

Wut?

The stock suspension setup is very poor, it can easily be improved upon.
Due to the sway bar triangulating the suspension (which is a stupid design) the lower control arm needs to follow an arc, adding in braces hinders this movement.

John covered this pretty well.

[Will F.]

Someone (in Germany I think?) used a similar design at one point - to use a solid tubular link between the back of the front lower control arm and the frame bolt. They went a step further and welded a bracket onto the frame to put the link in double shear at the frame. However, I believe they removed the brace again after testing.... I'll have to try and find that thread.

My only concern with making the lower control arm completely unable to deflect backwards by using a solid link like this (rather than the flexible one offered by Ed Uding), is that it would seem to me that you are introducing tension into the system.

The sway bar is mounted to the front frame extension and to each lower control arm. If you picture removing the lower control arm / spring / shock from the car, and just leaving the sway bar attached to the frame extension - as you lift it up and down it pivots on that frame extension mounting point, and the ends of the sway bar travel up and down in an arc, not in a vertical straight line.

Now put the suspension back in place, along with your solid link, which causes the lower control arm to travel straight up and down and does not allow any rearward deflection. The swaybar end is bolted to the lower control arm, which now prevents the sway bar from traveling in the arc - therefore there is now tension in the system as it goes through upward motion. So as the suspension compresses, and does not allow the sway bar to travel in an arc any longer, what is happening to the sway bar? Does the sway bar bend to mitigate (and over time will this cause metal fatigue)? Maybe the sway bar bushings are able to compress enough to take up the strain, without causing the sway bar to bend? I don't know, but I imagine this is why Ed's solution allows the braces to flex somewhat.

I'd love to see a solution which fully triangulates the lower control arm like what you are proposing here, so long as the movement of the sway bar is taken into account. On later mode Lotus Esprit's, I believe they added a very similar brace as what you are proposing, but (please correct me if I am wrong) they did this in conjunction with making a slide bushing on the end of the sway bar, so that it was able to still travel through it's natural arc while the lower control arm was prevented from deflecting backwards any longer. Maybe another solution would be a different sway bar mounting to the lower control arm using a drop link rather than a direct attachment.

Thanks,
John

John Thank you for this. This is excellent information. I wonder if the use of spherical heim joints would allow more of an arc then just a polyurethane bushing. I do however agree with Josh "
I have a project coming up this winter, which will use sway bar end links (like most cars) to get around this issue." having a sway bar with an end link is definitely a far better way to go, not to mention would add worlds of tunability. But this in turn would also require a 2nd brace on each side. At this point I would probably be easier to just make a custom lower control arm, and use the outer points of the original lower control arm mounting. That way there is a true triangular set up, and would achieve none of this arching that is cause by the sway bars attachment style.