Jumping off the Diesel Bandwagon - UPDATED
Well, after two Cummins diesels that I thoroughly enjoyed, I am going to place a factory order for a RAM 2500 with the 6.4L Hemi, 4.10 gears, rear air suspension, Laramie and plenty of added options. ...
Forum Discussion
...
Nice pic of the rear suspension, ib516. I did discuss it back here earlier, and it nice to actually see it.
Now it can be plainly seen how the third anti-wheel-hop shock works. It is needed because the rubber bushings in the 4-link set-up have (and must have) enough give to allow some arm-twist rotation as in when the truck leans around a corner. This give also allows some fore-aft in link length that can permit an axle rotation oscillation known as wheel-hop or axle tramp.
Those critical of coils over leaf springs may need to rethink stability as there is considerable undesirable lateral movement in hotchkiss type leaf suspensions. The typical leaf set-up is just barely stable enough to furnish reasonable lateral axle placement and moderately resist hop by itself. This Ram set-up is undoubtedly quite a bit superior and does cost the OEM a bit more to manufacture. Leaf suspensions are popular because they are cheap with a low part count (leaves are merely cut out), not because they are better. As ib516 mentioned, nearly all modern railroad rolling stock and locomotives use coils exclusively, so there is proof that no inherent weakness exists in coil use.
From the picture we can see that there are two vertical links seemingly going up nowhere behind the axle. I would surmise these go to sway bar ends, the center of which is allowed to rotate in a pair of brackets mounted solidly on the frame. Directly behind the axle is a horizontal, classic Panhard Rod that is called something else by Ram when they previously used it on the front steering axle. This type bar is also on the front of both my 3/4 ton "live axle" Ford 4x4's and is called a track bar by Ford, I believe. Note that the front springs are cheap leaf springs, and these typical leaves are nowhere near enough stable to insure steady steering without the axle going somewhat side-to-side with the pitman arm, thus the track bar.
I am intimately familiar with the 4-link coil suspensions since my 5.0 Mustang used a similar system. Instead of parallel with the lower, Ford moved the rear of the top 2 links inward towards the pumpkin to form a triangle. The intent was to make them keep the axle placed laterally without using a Panhard Rod set-up. It worked, but not as well as a Panhard Rod would have. Lower part count cost less. Ford used a pair of "axle dampers" near each tire to control axle wrap/wheel hop/axle tramp for the same reason as Ram, that of rubber bushing give.
The triangulated upper arms did provide a measure of axle placement, but the angle created a bind in the rear suspension when in a hard turn. This problem showed up as inside wheel lift which caused the outside tire to do all the work. When one tire does all the work, there is a loss of traction making the rear end naturally a little loose. Believe it or not, a soft compliant rear end provides equivalent tire loading and better traction.
I think Ram has largely avoided this traction loss by using parallel arms and a Panhard Rod. I salute the Ram design team.
I could go on about roll centers etc, but rest assured that Ram has done a better job than Ford in the potential handling department. And they are worlds ahead of the low cost spring leaf crowd.
Wes
...
Nice pic of the rear suspension, ib516. I did discuss it back here earlier, and it nice to actually see it.
Now it can be plainly seen how the third anti-wheel-hop shock works. It is needed because the rubber bushings in the 4-link set-up have (and must have) enough give to allow some arm-twist rotation as in when the truck leans around a corner. This give also allows some fore-aft in link length that can permit an axle rotation oscillation known as wheel-hop or axle tramp.
Those critical of coils over leaf springs may need to rethink stability as there is considerable undesirable lateral movement in hotchkiss type leaf suspensions. The typical leaf set-up is just barely stable enough to furnish reasonable lateral axle placement and moderately resist hop by itself. This Ram set-up is undoubtedly quite a bit superior and does cost the OEM a bit more to manufacture. Leaf suspensions are popular because they are cheap with a low part count (leaves are merely cut out), not because they are better. As ib516 mentioned, nearly all modern railroad rolling stock and locomotives use coils exclusively, so there is proof that no inherent weakness exists in coil use.
From the picture we can see that there are two vertical links seemingly going up nowhere behind the axle. I would surmise these go to sway bar ends, the center of which is allowed to rotate in a pair of brackets mounted solidly on the frame. Directly behind the axle is a horizontal, classic Panhard Rod that is called something else by Ram when they previously used it on the front steering axle. This type bar is also on the front of both my 3/4 ton "live axle" Ford 4x4's and is called a track bar by Ford, I believe. Note that the front springs are cheap leaf springs, and these typical leaves are nowhere near enough stable to insure steady steering without the axle going somewhat side-to-side with the pitman arm, thus the track bar.
I am intimately familiar with the 4-link coil suspensions since my 5.0 Mustang used a similar system. Instead of parallel with the lower, Ford moved the rear of the top 2 links inward towards the pumpkin to form a triangle. The intent was to make them keep the axle placed laterally without using a Panhard Rod set-up. It worked, but not as well as a Panhard Rod would have. Lower part count cost less. Ford used a pair of "axle dampers" near each tire to control axle wrap/wheel hop/axle tramp for the same reason as Ram, that of rubber bushing give.
The triangulated upper arms did provide a measure of axle placement, but the angle created a bind in the rear suspension when in a hard turn. This problem showed up as inside wheel lift which caused the outside tire to do all the work. When one tire does all the work, there is a loss of traction making the rear end naturally a little loose. Believe it or not, a soft compliant rear end provides equivalent tire loading and better traction.
I think Ram has largely avoided this traction loss by using parallel arms and a Panhard Rod. I salute the Ram design team.
I could go on about roll centers etc, but rest assured that Ram has done a better job than Ford in the potential handling department. And they are worlds ahead of the low cost spring leaf crowd.
Wes
...
