Radius Arm Flip

[Shinichi]

I think both parties are right on this. Putting the control arm on top, bottom, or middle of the axle does not change the path of wheel/axle travel, but it will certainly change how the axle reacts to all the forces it is subject to...

Try this. Hold you arm down at an angle(30, 45 degrees doesn't matter) walk in to a wall with your arm and hand leading. Now do the same thing with your arm horizontal, or even 15 degrees down. Your arm pivots the same regardless, but will react to the wall very different...

 

[MYSHERPA]

My hand went through the wall in both cases.

 

[Shinichi]

You're going to fast

 

[-Spike-]

You can change the angle of the arm all you want; if you don't change the beginning and end points of the line the force follows, you don't change the geometry. Period.

 

[Ebag333]

You can change the angle of the arm all you want; if you don't change the beginning and end points of the line the force follows, you don't change the geometry. Period.

If this were true than adjusting the axle side of any link system would have no effect.

The force begins with the tire, ends with the frame.

Yet suspension design dictates that different link positions causes different behavior.

We don't have UCA's, but the principle still applies.

 

[Shinichi]

Makes senses that dropping the fixed side like the MAF brackets would actually change/correct the true angle, but do flipped control arms at least allow the fixed bushing to work better?

 

[Ebag333]

Makes senses that dropping the fixed side like the MAF brackets would actually change/correct the true angle, but do flipped control arms at least allow the fixed bushing to work better?

Flipping the arms has zero effect on the fixed bushing.

 

[LandCruiserPhil]

Flipping the arms has zero effect on the fixed bushing.

This ^^^is only true if you are under the belief control arm bushing binding is exactly the same for a stock truck and one with 4" of lift or a control arm angle change of ~7°.

More hi-jacking going on^^^

 

[Brunt Force Trauma]

I am just thinking logically here. I am not good at geometry. But by putting the arm on top wouldnt you be in effect lessening the amount it has to travel when the axle droops since you lengthening the distance from the axle to frame mount at ride height? With a panhard, as a live axle travels down on one side it also has to travel slightly left or right correct? So the farther the control arm has to travel the more binding there will be in the frame side mount. IIRC when I pull of my tires and shocks, and cycle my axle, the only thing keeping it from drooping more is the control arm binding in its mounts. It seem like being on top would allow a couple extra inches of down travel before it would bind up. Am I way off on this?

 

[Ebag333]

This ^^^is only true if you are under the belief control arm bushing binding is exactly the same for a stock truck and one with 4" of lift or a control arm angle change of ~7°.

More hi-jacking going on^^^

As I understand it, bushing binding is more a problem on the axle side than the frame side.

Since trucks with the MAF drop bracket don't seem to flex any better than trucks with, that seems to back that up.

 

[Walking Eagle]

Once again to quote MAF:

Doesn't matter how many times you quote MAF - MAF drop bracket change the point the axle rotates around, which is something different than changing the shape of the arm (what a arm flip does)

The fact is that the angle of the arms does have an effect on how it handles various forces. It's not the height of the frame bracket mount to the frame that matters, it's the angle of the arms.

Yep, the angle of the EFFECTIVE arm does infact effect handling

So as I've pointed out before, a control arm flip does the same thing that the MAF drop bracket does, just on the opposite end of the link.

Nope, one changes the point at which it rotates about, one doesn't

Look, this is basic geometry here. Here's some basic facts.

1) The length of the arm controls the radius of the circle that the end point (axle mounts) will travel around the pivot point (frame mount). Since we're not changing the length of the arm, that circle stays the same meaning that the end point (and axle, since it's attached) will always follow the same path. This has never been in dispute.

yes, and no. technically, since the axle gets moved forward slightly the radius of the circle gets slightly larger, probably not enough to worry about.

2) The angle of the arms determines at what point in that path the end point (axle mounts) exist. If you lessen the angle, the end point has to move up to 90* or 270* (assuming the end point starts below the pivot point). If you increase the angle, the end point moves down towards 180*.

Nope, the path of the axle is determined by it's distance from the pivot point (frame mount). The only way to reduce the forward and backward movement of the axle is to get it as close to a horizontal line from the axle center to the frame pivot. Less lift, or MAF brackets.

If the axle is moving forward and back, it's worse for handling, braking, etc than if it's moving perfectly straight up and down. This is why the drop arm or control arm flip both improve handling/braking/etc.

That much is correct.

 

[-Spike-]

If this were true than adjusting the axle side of any link system would have no effect.

The force begins with the tire, ends with the frame.

Yet suspension design dictates that different link positions causes different behavior.



We don't have UCA's, but the principle still applies.

Your quoted article is addressing a completely different dynamic, that of twisting the axle on its axis during suspension cycling via the different lengths and angles of upper vs. lower control arms in a 4 link setup. (Actually it's not referring to axle twist, see post #97, but the rest of this still applies, only more so.) The principle does not apply to radius arm geometry in any way. We can argue this all night, but the physics say the force travels between the two points, regardless of arm shape or position.

 

[Walking Eagle]

Yes it does move in the same path but I would think that having the arm at less of an angle would affect how it handles

Where there is some gain is the bushings mounting the axle are closer to horizontal with the pivot point (frame side). So there is a little less forward and backward movement of one side relative to the other at the bushings (not at the axle), so there may be less bind in the bushings. Though I believe much of that bind has to do with the axle trying to be twisted like a swaybar as one side tries to make it move clockwise and the other side (durring articulation anyway) tries to make it twist counter clockwise. How much bind is caused by each? I don't know, but the binding from twisting is what wristed arms alleviate, so I'm guessing that's the lion's share?

 

[Walking Eagle]

From the look of your picture by putting the arms on top of the axle it definitely decreases the angle of the arm
Why would it not make them more parallel to the frame than being under the axle?
At six inches of lift the front arm angle is pretty drastic and I dont think it was designed to run a that type of angle
I have noticed that when going to climb something that the front seems to want to walk under the vehicle and the front of the truck wants to raise up by the seat of the pants gauge
And I think that is do to the arms being at such a steep angle

It's hard for people to do, but honestly ignore the arm. Look at the axle and the pivot point. The more vertical difference there is between the two, the more the front is going to want to walk under the vehicle.

Simple freebody diagram. The force at the axle creates a moment. You calculate the moment by taking the force times the distance "y". If the force remains the same, the moment is the same if it's supported by the black line, the red line, the green line, or any other line (structure) you draw from the pivot point (the frame mount) and the point at which the force is applied (the axle). The only way to change the moment that is created for the same force is to reduce "y". The only way to reduce "y" is to drop the pivot point (MAF brackets), or to raise the axle in relation (less lift). This isn't guessing or feeling, this is straight out of any statics book.

Same deal for any force in the verticle direction, though then it's a force in the Y direction and the distance that matters is "X".

The one extreme of course would be to have the axle directly under the pivot at which point it would take very little force to create a large moment and move the axle back. The opposite extreme would be to have the axle in line with the pivot point, which no matter how much force you put on it, it would never create a moment (movement).

Take a t-square if you have one. Hold onto one end of the long side with your right hand. We'll call that the frame side. Now take your other hand and push straight toward your right hand on the long side. The T-square might try to bend, but it won't try to rotate around your right hand as long as you are pushing directly toward it. Get a little off line and it will want to rotate. Now, take your left hand and grab the short end of the t-square. Push it directly toward your right hand. It'll do the same exact thing. The shape of the arm doesn't matter if it's straight or angled. Now, flip that T-square upside down so the angled side is pointed down. You've just flipped your radius arms from the top to the bottom. Do the same thing. Same result. It works the same for generating a moment if your off center on your pushing, but I can't tell you to feel the moment it generates and see if it's more or less unless you can always generate the same force and you have a third hand to feel the moment.

 

[-Spike-]

T-square analogy is fantastic.

 

[Walking Eagle]

T-square analogy is fantastic.

Thanks. Though on this forum, I'm waiting to see who points out that I should have said framing square not t-square

 

[-Spike-]

Your quoted article is addressing a completely different dynamic, that of twisting the axle on its axis during suspension cycling via the different lengths and angles of upper vs. lower control arms in a 4 link setup. The principle does not apply to radius arm geometry in any way. We can argue this all night, but the physics say the force travels between the two points, regardless of arm shape or position.

What's even funnier, now that I reread the article, I figured out what was bothering me about it. That article is talking about upper and lower control arms on an independent suspension. Camber doesn't change on a solid axle.

 

[kidglove13]

Its framing square not a T square
That does explain it better
I guess the only real test would be to just do it and test it and use seat of the pants gauge
I am not ready to do this yet
Hopefully the Tom.Korn will have some more testing results for us shortly

 

[adventr]

Its framing square not a T square
That does explain it better
I guess the only real test would be to just do it and test it and use seat of the pants gauge
I am not ready to do this yet
Hopefully the Tom.Korn will have some more testing results for us shortly

I can already tell you that the flip does everything that I wanted it to accomplish. That is:

- Make my lifted (8"+) rig drive like stock
- Move axle back to center of wheel well
- Retain Toyota factory bushings (good quality)


Honestly, I'm not really concerned with adding flex to the front end on this rig. If I wanted more flex, I would have built a 3-link, and that would've been about the same amount of work as doing the arm flip.
Reason I didn't do a 3-link? I wanted to retain the driving characteristics of the 80 series. Some people will say that a properly setup 3-link will drive better than the radius arm setup, and that may be true, but it's not the norm. I just wanted to be able to drive this thing across the country, run some trails, and drive it back. The radius arm flip turned out to be perfect for my needs.

 

[Walking Eagle]

I can already tell you that the flip does everything that I wanted it to accomplish. That is:

- Make my lifted (8"+) rig drive like stock
- Move axle back to center of wheel well
- Retain Toyota factory bushings (good quality)

-Gained lots of ground clearance.
-Gained clearance around tie rod

And you have something really kool that no one else on mud has! Sorry there has been so much debate on this thread.