I'm going to be prototyping a single pivot conversion adapter. It will bolt through the factory lower ball joint holes and move the control arm pickup as far out as possible so as to affect scrub radius as little as possible. It will also use a double shear connection. This would allow the fabrication of a one piece lower control arm and allow for caster adjustment.

What're your thoughts?

Here's a simplified version of what I'm talking about:

This was discussed in the 2g k member build.

It starts at post #115

https://www.dsmtuners.com/threads/2g-tubular-front-k-member-build-share-ideas.455822/page-5

lasthope05 said:

This was discussed in the 2g k member build.

It starts at post #115

https://www.dsmtuners.com/threads/2g-tubular-front-k-member-build-share-ideas.455822/page-5

Click to expand...

Thanks, indeed it was, but the discussion was dropped in that thread after Paul found the ball joint that works. My concept differs in that it eliminates the need for a separate compression arm and that it moves the pivot as close as possible to the brake rotor.

Well if it works I'm intrigued. I hate that weird complex setup down below.

So one major issue with running a 1-pc a-arm is that it requires a custom k-member because you'll need the inboard pick-up point of the compression arm moved quite a bit to be inline with the LCA pick-up point to avoid binding.

As well, I remember Andrew Brilliant making some good points about the benefits of the double lower balljoint for road racing and autocross, but it's been so long, I'm a little hazy on the subject. I could see this being a pretty great weight savings idea for a drag car though.

99gst_racer said:

So one major issue with running a 1-pc a-arm is that it requires a custom k-member because you'll need the inboard pick-up point of the compression arm moved quite a bit to be inline with the LCA pick-up point to avoid binding.

As well, I remember Andrew Brilliant making some good points about the benefits of the double lower balljoint for road racing and autocross, but it's been so long, I'm a little hazy on the subject. I could see this being a pretty great weight savings idea for a drag car though.

Click to expand...

Not if you use a heim where the shaft travels horizontally through. Think something like this:



You could adjust caster by adjusting the spacers on the back heim as you lengthen/shorten it.

TSiAWD666 said:

Well if it works I'm intrigued. I hate that weird complex setup down below.

Click to expand...

Indeed. Not to mention shaving some weight from the big forged steel parts.

RWD4G63 said:

Not if you use a heim where the shaft travels horizontally through. Think something like this:

Click to expand...

Thise inboard pick-ups look to be inline with each other in that pic. Try moving one outward 6" and The arm wont articulate without binding.

I know someone who built such a 1-pc arm with heims and it just didn't work with the OE inboard pick-ups.

99gst_racer said:

Thise inboard pick-ups look to be inline with each other in that pic. Try moving one outward 6" and The arm wont articulate without binding.

I know someone who built such a 1-pc arm with heims and it just didn't work with the OE inboard pick-ups.

Click to expand...

Are you saying the arm won't articulate enough, or at all? This would definitely be for stiffly sprung cars with limited suspension movement anyway. I feel like there has to be a way to orient the heims so articulation is available.

https://www.dsmtuners.com/threads/2g-suspension-analysis-and-testing-rig.521843/

RWD4G63 said:

Are you saying the arm won't articulate enough, or at all? This would definitely be for stiffly sprung cars with limited suspension movement anyway. I feel like there has to be a way to orient the heims so articulation is available.

https://www.dsmtuners.com/threads/2g-suspension-analysis-and-testing-rig.521843/

Click to expand...

There is little articulation. Not enough to be useful or road worthy. It binds badly.
You'd have to move one of the pick-up points to be inline with the other, and then you're good to go. (Either the LCA pick-up out, or the compression arm pick-up in) Not a simple undertaking, but certainly possible.

Anothet thing I'd be leary of is running a heim instead of a balljoint. Being that the axial capacity of most any heim is only 10-15% of it's radial load capacity, and given that the shock and spring attach directly to the LCA on the 2G, that's quite a bit of axial load on that heim. I'd personally only feel comfortable with such a set-up when the suspension is attached to the spindle rather than the LCA. Just my opinion, of course.

99gst_racer said:

There is little articulation. Not enough to be useful or road worthy. It binds badly.
You'd have to move one of the pick-up points to be inline with the other, and then you're good to go. (Either the LCA pick-up out, or the compression arm pick-up in) Not a simple undertaking, but certainly possible.

Anothet thing I'd be leary of is running a heim instead of a balljoint. Being that the axial capacity of most any heim is only 10-15% of it's radial load capacity, and given that the shock and spring attach directly to the LCA on the 2G, that's quite a bit of axial load on that heim. I'd personally only feel comfortable with such a set-up when the suspension is attached to the spindle rather than the LCA. Just my opinion, of course.

Click to expand...

That does make sense now that I picture the movement in my head. Seems like it would be easiest to space out the inner control arm pivot with a simple bracket or welded extension of the subframe. I do have the equipment to measure bumpsteer and camber change over suspension travel, so I can confirm whether this will be helping and hurting haha.

Also, I'd definitely want to use a spherical bearing and cup welded to the arm in the outer pivot. The way I would design the bracket it would be in double sheer. I definitely understand that a rod end in bending is no good. It would be similar to your current lower arm design, just a bit shorter than the ball joint you have on the end.

What your gaining in caster you will loose in caster or more when turning as you will no longer have a virtual pivot and your pivot now alters. You will loose some corner grip as you wont get the camber gain the pivot gives you throughout its range, 1 piece arms can be lighter and stronger sure but its not always the best way depending on end goals.

You also wont some positive scrub radius. It works alot better for our cars, at least it will help with the steering side of things for you.

Yes, there will be some positive scrub radius added. I don't think it's the end of the world. The dual pivot definitely helps with torque steer. With this done right you can either add additional caster trail into the design or add static caster with the arm. I doubt it's going to be detrimental to turning. If you need more camber gain on the outside wheel, run more static negative camber by shortening the upper arm. Lengthening the arm while keeping the shock mount in the position it is will also increase the motion ratio, meaning spring rates might need to increase slightly.

Trying my best to approximate what I'm saying with the stock parts.



You could try it this way with a ball joint:



Or double shear:

This is hard to line up perfect, but the inner pivot would need to move out about this much (which is close to the amount the mount on the knuckle moves out):

Have you thought about the whole car as a whole with the adjustments your wanting to do?

Your going affect the camber, bumpsteer, toe, roll center and those are just some of the ones im thinking of as i just woke up. Some of it is counter fixable but some need other items made to go along with the lower arms.
If your wanting the BJ or spherical that low then i dont agree as your going to hate handling and its effects and screw up the rear of the car also

ec17pse said:

Have you thought about the whole car as a whole with the adjustments your wanting to do?

Your going affect the camber, bumpsteer, toe, roll center and those are just some of the ones im thinking of as i just woke up. Some of it is counter fixable but some need other items made to go along with the lower arms.
If your wanting the BJ or spherical that low then i dont agree as your going to hate handling and its effects and screw up the rear of the car also

Click to expand...

My two main concerns are bumpsteer and suspension travel. Bumpsteer is relatively easy to change with spacers or physically moving the tie rod pickup. Roll center is only affected by half the amount that you move the lower pivot, so not a major deal there. The camber curve will definitely change, but increasing the change under bump seems like it would be advantageous.

Why do you say I'm going to "hate handling"? Do you already have information on how this will turn out? The factory arrangement is definitely not God's gift to awd cars or anything, it leaves a lot to be desired in a race environment.

The only thing I'm affecting that has to do with the rear is roll axis inclination, and it will change minutely. I don't understand how you think this will mess with the rear suspension. It will definitely affect the front grip, which may mean some changes to the rear alignment or roll resistance, but that's actually the goal. I have the equipment to test camber and toe change (bumpsteer). I won't go through with it if it doesn't represent an advantage besides weight, as we all know there's more to it than that.

RWD4G63 said:

My two main concerns are bumpsteer and suspension travel. Bumpsteer is relatively easy to change with spacers or physically moving the tie rod pickup. Roll center is only affected by half the amount that you move the lower pivot, so not a major deal there. The camber curve will definitely change, but increasing the change under bump seems like it would be advantageous.

Why do you say I'm going to "hate handling"? Do you already have information on how this will turn out? The factory arrangement is definitely not God's gift to awd cars or anything, it leaves a lot to be desired in a race environment.

The only thing I'm affecting that has to do with the rear is roll axis inclination, and it will change minutely. I don't understand how you think this will mess with the rear suspension. It will definitely affect the front grip, which may mean some changes to the rear alignment or roll resistance, but that's actually the goal. I have the equipment to test camber and toe change (bumpsteer). I won't go through with it if it doesn't represent an advantage besides weight, as we all know there's more to it than that.

Click to expand...

I do have reasons for the front to upset the rear. I have a custom rear subframe maxed out to help speed up the rear towards the front and it still wont. The front is just too sharp and makes the rear roll too much for my liking.

Lower arm adjustments move the R/C alot more then the upper arms do and has a greater effect. On the front it works alot more then the rear does from what i know thus far.

Moving your lower arm out or spacing it out without the upper arm will throw some results i think will shock you, camber gain will be drastic per 1/4" the motion ratio will alter too so bare that in mind when shoosing springs since the shock mounting will now be different.
I wish i had my setup in my software so i could do a before and after but everytime i go to do it i get something else in the way so i have to stop that. But i need to do this and then its done

ec17pse said:

I do have reasons for the front to upset the rear. I have a custom rear subframe maxed out to help speed up the rear towards the front and it still wont. The front is just too sharp and makes the rear roll too much for my liking.

Lower arm adjustments move the R/C alot more then the upper arms do and has a greater effect. On the front it works alot more then the rear does from what i know thus far.

Moving your lower arm out or spacing it out without the upper arm will throw some results i think will shock you, camber gain will be drastic per 1/4" the motion ratio will alter too so bare that in mind when shoosing springs since the shock mounting will now be different.
I wish i had my setup in my software so i could do a before and after but everytime i go to do it i get something else in the way so i have to stop that. But i need to do this and then its done

Click to expand...

You need more rear roll resistance dude. The upper and lower arms are the only things that determine roll center, so they affect it equally.

Also, moving the rear arm position is going to affect anti-squat, which is probably some of what you're feeling as well.

RWD4G63 said:

You need more rear roll resistance dude. The upper and lower arms are the only things that determine roll center, so they affect it equally.

Also, moving the rear arm position is going to affect anti-squat, which is probably some of what you're feeling as well.

Click to expand...

anti squat is not what I have as its the rear thats the issue not the front but the front is upset and cas caused the rear to become more noticed.

I already have alot of resistance, more then mst infact its still not the issue and i knw the cause and working on it, im just letting you know the effects will be similer to what you will see

ec17pse said:

anti squat is not what I have as its the rear thats the issue not the front but the front is upset and cas caused the rear to become more noticed.

I already have alot of resistance, more then mst infact its still not the issue and i knw the cause and working on it, im just letting you know the effects will be similer to what you will see

Click to expand...

Anti-squat is a property of all automotive suspension, it's just called anti-lift or anti-dive in the front and anti-squat in the rear. It is usually given in a percentage. I'd be interested in seeing where the 2G sits when lowered. I'll have to check that out tonight actually, it's been a while.

What's your rear spring rate?

Theory confirmed:



My moving the rear arms up and not the rear trailing arm, you've massively decreased the anti-squat of the rear suspension. This will make it feel soft, especially on corner exit.

RWD4G63 said:

Theory confirmed:

My moving the rear arms up and not the rear trailing arm, you've massively decreased the anti-squat of the rear suspension. This will make it feel soft, especially on corner exit.

Click to expand...

corner exit is not my problem, its corner entry. its rolls on its side sets and then sits fine on exit but the initial set has too much roll, raising the rear arms up did help hugely but not enough (close though)

RWD4G63 said:

Anti-squat is a property of all automotive suspension, it's just called anti-lift or anti-dive in the front and anti-squat in the rear. It is usually given in a percentage. I'd be interested in seeing where the 2G sits when lowered. I'll have to check that out tonight actually, it's been a while.

What's your rear spring rate?

Click to expand...

i have 784Lbs in the rear which is 14kg they use here. when i did the bacis drawing of the angles it only seemed to upset the toe more, it still has a raised arm so its still acting like its going through its motion range but i get its the only arm thats not altered and i likely can alter it soon and add some extra holes

My point is you've decreased the suspension's resistance to compression forces. Raising the roll center will help, but you've gone one step forward and two steps back. Drop that lower arm back down and dial in the bumpsteer and I think you'll be pleasantly surprised.

RWD4G63 said:

My point is you've decreased the suspension's resistance to compression forces. Raising the roll center will help, but you've gone one step forward and two steps back. Drop that lower arm back down and dial in the bumpsteer and I think you'll be pleasantly surprised.

Click to expand...

so what your saying is lower the rear roll center. i had it one lower then the rear toe arm once but did not feel that but i did not have it back in the stock hole right at the bottom.

see in my mind im always visualizing the system, but this rear roll center dropping does not seem to compute it will also mean my arms will be now below the outer mounting or just about so any compression will result in camber loss

It's all a balancing act. Any amount you move those arms is only moving the roll center roughly half that amount anyway, as you have to take the upper arm into account. If you could move the upper control arm up as well, now we'd be talking about some serious roll center correction. In fact you could probably angle it as well to dial in some more anti-squat. There will always be some compromise, you just have to find out which is best for performance. I'm just trying to get to the root of your soft rear issue.

Here is a very crude and not accurate approximation of the anti-squat lines of a 2G rear suspension. Looking at them you can see that in factory position, the 2G has a pretty neutral amount of anti-squat, and it goes farther pro-squat when it's lowered. I can say with almost perfect certainty that your rear-suspension is now pro-squat.