RE: Re: anti-wrap via radius arms (was RE: JPOR: Bigger lift options.)

[Larry Soo <lars@xxxxxxxxx>]

Ed, I'm cc'ing this to the Joffroad list since I'd like to get others'
opinions on this...plus I want to get as much mileage as I can from the
ASCII "art" I made.

At 05:16 PM 2000-02-24 , you wrote:

>Okay, now I'm _really_ confused. :-)

Then I'm probably the last person you should turn to for an explanation.  <g>

>Since the radius arm (unlike a 3 or 4 link system) will keep
>the axle housing from rotating in relation to the arm, it will
>change the pinion angle (in relation to the t-case yoke) upon
>compression/droop.  So the only advantages I see by duplicating
>the arc/movement described by the driveshaft are that if you're
>running a CV joint at the t-case side of the driveshaft, the
>pinion angle will remain neutral throughout the travel of the
>axle.

I'm running a CV joint.  If you want to keep the angle the same at all
times, then you're looking at some kind of parallelogram type of setup,
like a 3- or 5-link.  And even then, the arm placement is critical: the
vertical & horizontal distance between the two links' (assuming four links
and a panhard rod, when I talk about "the two links," I mean the left pair
or the right pair) frame mounts need to be the same as their axle end
mounts'.  Some difference is ok since the resulting change in pinion angle
might be neglible for our purposes.

>Additionally by locating it as close as possible to the
>center of the axle housing, you also reduce the amount of total
>travel necessary for the arm.

Yes, you're right.

>Is there another reason that I'm
>missing?

I think so.

Top view of axle:

w = wheels
t = axle tube
D = diff
R = radius arm mounted to axle
r = radius arm
f = radius arm mounted to frame

f
w              r  w
w             ar  w
wttttttttDtttttRttw
w                 w
w                 w

In this example, the angle, "a", is 90 degrees to the axle tube, measured
against the horizontal plane.

Now, when the right hand wheel droops, the radius arm must continue to
point at "f", the frame mount.

Angle "a" can no longer be 90 degrees because the axle is no longer
parallel to the ground.  Hence, the radius arm needs to be able to twist so
it can continue to attach to the frame.

f
w            r    w
w            ar   w
wttttttttDtttttRttw
w                 w
w                 w

In this example, we attach the arm so that angle "a" is more acute and lets
the frame end of the radius arm to attach closer to the center of the
vehicle.  Now, when the right side droops, angle "a" can stay closer to its
original value because the distance between radius arm mounts "f" and "R"
stays relatively consistent.

Does that make sense to you?

Now, I don't know how important this is.  All I know is that it should
reduce the amount of lateral bending required of the arm.  That, in turn,
should result in less resistance to articulation.  But whether or not we're
talking about amounts that we will notice, well, I can't answer that.


...lars

http://www.bc4x4.com Canada's biggest 4x4 site