Ugg... This is what happens when something tries to be explained in simple terms... Somebody will find "fault" with the explanation, because it's not completed.

It's YOUR fault I'm about to put the better part of the known world to sleep in what follows below. I hope your f*ing proud... You brought this on yourself.

Given:

Rig A:

5" leaf pack droop travel beyond the "at rest" position.
5" travel from revolver shackle opening up.

Rig B:

10" leaf pack droop travel beyond the "at rest" position, attched with a standard shackle.

Items of interest:

Both rigs have the exact same tires, open differentials, are the same make/model, have equal lift heights, and are driven by the same driver: Goofy.

So Goofy goes out and gets himself into a position where both front tires are on the ground. His rear axle, however, has a rock on the passenger side, pushing that side tire up. The driver's side is drooping into a hole, so far that the leaf suspension is completely at it's lowest position.

Here's what happens to the leaf suspension vs. traction, as the driver's side drops.

When the passenger side tire gets pushed up onto the rock, there is a traction increase (due to leverage) on the driver's side. This increase will be evident for as long as the leaf spring is in it's range of motion. The leaf spring has a particular spring rate (I'm sorry; I can't compare "progressive" springs in this explanation because they are just too complex, and too many variables) through it's range of motion.

As soon as the leaf spring passes through it's neutral point, it is subracting down force (it's pulling upwards), thereby reducing traction available.

To make life easier, we'll throw some numbers in so it makes since.

We'll estimate that there is 1000 lbs force downward on the wheel when the truck is at rest (800 lbs of vehicle weight, 200 lbs of tire/axle weight), and if the passenger side adds another 100 lbs force, then when the leaf is at it's neutral axis, it has 1000+200 = 1,200 lbs of downforce at this point.

We also know that a REVOLVER shackle will not open up unless there is no weight of the truck pushing it closed. A revolver only opens up when the weight of the tire and axle alone can pull it downwards. As TJ says, and I don't disagree, the revolver is not "spring-loaded". It doesn't unload at random; all the weight of the vehicle has to be off, and the axle/tire combination has to be in a position to PULL it downwards/open.

When a leaf spring has passed the neutral axis, it is pulling UP on the tire/axle combination. When the leaf spring has reached it's final droop point, it is pulling up on the tire/axle as much as it ever can; it has reached it's maximum negative (upwards) force.

Anybody that's ever been to this point can tell you that once a leaf spring gets to that point, that's all she wrote for traction. At this point in time, the leaf spring is pulling up at a value that negates the force from the fulcrum, and the weight of the tire. If it weren't negating that force, it wouldn't be at it's farthest droop limit; the two points coincide. And finally, the weight of the truck is completely gone at this point as well, elsewise the suspension couldn't be maxed out in droop.

So to summarize, when the leaf spring reaches it's final suspension droop limit, there is no further downwards force being applied. Force at this point equals 0.

Now in Rig 2, from the point of neutral to the point of full droop (10 inches) of the leaf spring, using our numbers means for every 1 inch of droop, there's a loss of down-force equal to 1/10th of 1200, or 120 lbs. Take in mind, the frame of reference is the SPRING.

If you look at the down-force in table format:

Droop Downforce Remaining
0 1200 lbs
1" 1080 lbs
2" 960 lbs
3" 840 lbs
4" 720 lbs
5" 600 lbs
6" 480 lbs
7" 360 lbs
8" 240 lbs
9" 120 lbs
>10" 0 lbs

But what happens in a revolver? Why is is so special/different? Because the point that it loses traction is much, much sooner than the leaf setup.

From the analysis from before, when the leaf spring reaches it's farthest droop point, it's got 0 weight of downforce acting on it. This setup loses traction twice as fast as just the leaf spring setup (in our example) becuase the downforce at the spring has to equal 0 in only 5" of droop. Looking at the revolver's table, the reduction of force is:

Droop Downforce remaining
0 1200 lbs
1" 960 lbs
2" 720 lbs
3" 480 lbs
4" 240 lbs
5" 0 lbs

But wait. What happens for the remaining 5" of traction??? It can't be 0 lbs completely, because the weight of the tire and axle is still there, causing the revolver to open up. Very carefully, read this sentence. Don't go any farther until you understand what I'm saying. The frame of reference for down-force is the spring, as the Rig 2 has a spring, and Rig 1 has two components (spring AND hinged shackle). So far, we were looking at the force at THIS point of reference. The remaining 5" of travel the revolver has only has 1 force acting on it, ever, the weight of the tire/axle. The tables are now going to be "revised" to show the force AT THE BOTTOM OF THE TIRE, and not at the leaf spring:

Droop Rig 1 Force Rig 2 Force
0 1200 # 1200 #
1" 960 # 1080 #
2" 720 # 960 #
3" 480 # 840 #
4" 240 # 720 #
5" 200 #* 600 #
6" 200 # 480 #
7" 200 # 360 #
8" 200 # 240 #
9" 200 # 120 #
>10" 0 # 0 #

Some of you will be able to read those tables, and descriptions, and realize what I'm saying. Some of you will get lost in either the explanation, or the math, or both. But my point is, a REVOLVER shackle causes traction loss far sooner than an equivalent leaf pack, because of their design for how they get their travel.

The reason why the surface makes such a big difference, is there is a fixed friction force that has to be overcome to make the rig move, and that's universal regardless of what surface it's on, because that's the friction needed from the tire to vehicle interface, and not the tire to ground interface. It's not an airplane; the moving force has to come from the tire to surface contact; not outside engine thrust. That's very basic physics. I don't know what that number is; I will be flat-out shocked if anybody even knows what that number is.

But let's look at what happens to the tables when you consider Asphalt friction (0.8 coeff.) and Dirt friction (0.3 coeff.). Below are the tables, again, only with friction forces and not just down-wards force applied:

Droop Asphalt Dirt
Rig 1 Rig 2 Rig 1 Rig 2
0 960# 960# 360# 360#
1" 768# 864# 288# 324#
2" 576# 768# 216# 288#
3" 384# 672# 144# 252#
4" 192# 576# 72# 216#
5" 160# 480# 60# 180#
6" 160# 384# 60# 144#
7" 160# 288# 60# 108#
8" 160# 192# 60# 72#
9" 160# 96# 60# 36#
>10" 0 0 0 0

Let's look at the table for just a bit, then I'll shut up about it... Here are my conclusions:

IF it only takes 60 lbs of friction force of the tire to push the truck in the dirt, then in this example, a Revolver would have no drawback.

However, if it takes, say 200 lbs, then the Revolver's extra flex is completely useless, because the slippage occurs between only 2" and 3" of droop in Rig 1. But Rig 2 droops to between 4" and 5".

I don't know what the "magic number" is for how much friction is required to get the rig to move. That depends on a lot of things; loading of the rig, wheelbase, angle of the incline, etc. But it doesn't depend on the surface; the friction required to move is something inherent in the rig, and can only change when the loading of the rig changes, or the angle changes.

The friction of the tire to surface has to supply enough traction to overcome whatever that number is. Because unfortunately, this isn't like the airplane situation, and you do have to deal with two seperate force calcs to figure out how it'll be able to move.

Personally, I think my loading values were assumed too low. I also have a hunch it takes a helluva' lot more than 200 lbs of friction force available to get the rig to move. I know this, because my own personal weight ain't gonna' be enough to move the truck up a hill if I lean on it...

The tables very clearly show, though, how important it is to compare revolvers on a PARTICULAR rig, and not assume they are worthless/good on all rigs. The lighter the rig, the better/closer they will be to a proper leaf pack in the traction available.

I realize I have to revise my thinking, slightly, now that I've ran the tables. I admit, now, that in the last couple inches of travel, the revolver actually has MORE traction available than the leaf spring alone, if all the numbers are true. However, the HEAVIER a rig is, the closer the numbers are in this particular range, and since I think my weight numbers are estimated pretty light, that differece may be a wash. I don't know. But I do have to admit that in the last little bit of travel, the revolver will have a smidge more traction.

But the thing is, though, if it takes more than just some fat-ass leaning into the truck to make it move, then you won't even get to that point of usefullness, because once the tire starts to slip, it's over...

And the revolver setup loses traction at a MUCH higher pace than Rig 2. Hell, look at 5" down... On the dirt, Rig 2 has 3 TIMES the amount of available traction.... Again, pointless information if that's not enough to make the rig move, anyways, but still significant enough to mention...

And my FINAL note:

TJ: QUIT MAKING ME AGREE WITH JEFF ON SOMETHING!!! IT'S IRATATING! THE GUY SHOOTS FROM THE HIP TOO DYAM MUCH FOR ANYONE TO FOLLOW HIS ARGUEMENTS!! SO CAN WE please ARGUE SOMETHING WHERE HE AGREES WITH YOU NEXT TIME??