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Inboard shocks on burbs?????

Discussion in 'OffRoad Design' started by Muddytazz, Dec 17, 2002.

  1. Muddytazz

    Muddytazz 1 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Muddytazz
    White Beast


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    Re: Pics please of your lifts............ [re: Stephen]
    12/17/02 10:34 AM Edit Reply



    So a shock relocation kit would be a BAD idea?

    Its a Wheelbase Thing... You Wouldn't Understand
    CK5 SUB CULTURE

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    Re: Pics please of your lifts............ [re: Muddytazz]
    12/17/02 05:17 PM Edit Reply



    Stephen,
    I did a shock relocation on the rear of my suburban and it handles great. It actually rides and handles better than stock. The fact that it is a dually now may have something to do with it feeling real stable, but that shouldn't change body roll. Anyway's I haven't noticed any negative effects so far. If you could enlighten me and the others here as to why it is a bad idea in depth, it would be greatly appreciated.
    Mike

    [/ QUOTE ]
     
  2. 55Willy

    55Willy 3/4 ton status

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    Muddysub did one on his. You would need his feed back on this.
     
  3. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    OK, there are 2 basic problems with the inboard shock mounting:
    1. the shocks are mounted farther inboard and thus have less effect in body roll or articulation conditions. This effect is independent of shock mounting angle. Imagine if you had both rear shocks mounted straight up off the center of the rear axle. This is the extreme case obviously and in this situation you have no roll damping at all because the shocks will not compress or extend when the body rolls. You can have good ride damping in pure vertical bump travel since the shocks will actually move but cornering stability will seem like there is no shock at all.
    The best case is having the shock mounted as close to the wheel as possible, this will give you maximum motion out of the shock when the axle articulates (or consider the other way around and call it body roll). You can imagine a shock in this position will move a lot since any time the body rolls even a little, it will extend or compress the shock.
    All we can do when given mounting restraints is try to achieve the best shock mounting that we can, and obviously trying to mount the shock as close to the wheel as possible is the direction we want to go for effective damping in body roll or articulation conditions.

    2. Mounting angle has a lot to do with the amount the shocks travel. The factory tipped the shocks forward and backward for exact reasons that are unknown, but it did a couple things right. One is they do have a little effect on axle wrap since one shock is always in rebound (stiffest shock condition) when the spring wraps. The other is that when the body rolls the shocks lose very little of their effectiveness.
    With shocks tipped inboard at the top, you lose more motion under body roll conditions since the roll center of many leaf suspensions is a good way above the axle housing. The top of the shock moves less as the body rolls as you bring the top of the shock inboard. So again the ideal angle for the shock is straight up and down for it to be the most effective.

    Now it's pretty safe to say that all subs are top heavy since that's just the way they're built. A lot of K5's are in the same boat but at least there we have some options to lighten up the trucks.
    A top heavy truck will typically have a lot of body roll, depending of course on spring rate but in general the higher the CG and the more weight you have, the more body roll you're going to create. If you want to control this, you need effective shocks so that you don't get the truck "sloshing" around during sudden maneuvers or in offroad situations where the suspension is being excited by the terrain.

    A lighter vehicle can have decent success with highly leveraged shocks since they typically have less body roll to start with but even in that situation you're never going to have optimum damping in both vertical travel and body roll.

    Proper shock mounting has concrete rules, you can't mess with them. But, there is some gray area here as with all things. Some people's seat of the pants feel isn't good enough to tell the difference between good and bad mounting. Some people don't care about the handling drawbacks. Some suspensions are more tolerant than others, an example would be a 3/4T sub with a many leaf pack that doesn't get flexed much (leaves a little crusty) compared to a K5 3 or 4 leaf pack that's polished smooth with teflon inserts. The nice flexy spring will move more to start with and since it's polished and tuned to be smooth, it will have very little damping. Greasable bushings compared to rubber bushings fall in here also. A greased urethane bushing in the spring will let it move much more freely and offer no extra damping.

    Some examples of shock mounting I've come across (keeping in mind this is subject to my seat of the pants feel):
    My Project 'Burb. I'm running the TCI gas charged shocks in the stock location and for offroad use, it's underdamped in the rear. It rides and handles OK on the road but it could definitely use more roll damping offroad. Changing it around isn't a huge priority because it's not really meant to be a serious 4wd all the time but it may end up with the shocks mounted farther outboard to help this out.

    Project UAV. I drove the truck on a part of the Holy Cross City trail and one of the first things I noticed was it was pretty soft in roll. So I cranked up the RS9000's and then it was OK in roll but had a stiff ride. This is typical of the "tips together" mounts.

    My K5. I have soft springs and relatively soft shocks but it has good body roll damping without too much overall roll because the springs and shocks are mounted as far outboard on the axles as they can be without interfering with something more important. The thing has plenty of articulation and doesn't use up all of a 16" travel shock mounted in the best possible position.

    Toby Erwin's K5. We changed the rear shock mounts from the "tips together" method to outside the springs. Overall difference was huge. Much better feel in corners and no more feeling like the rear was uncontrolled. With the "tips together" mounts, the shocks moved 5-6" under articulation. With the new mounts, they moved between 10 and 11 inches. Nearly doubling the shock travel makes a big difference.


    The goal for everyone has been to stick as long a shock as possible in the chassis and use as little of it as possible when really the goal should be to mount a long shock and actually use all of it. And in the real world, I think you're going to find very few rear suspensions that will use up all of a 14" travel shock mounted near the wheel with a bit of forward angle and if you do there are now 16" travel shocks pretty commonly available. If you think you need more than that, you may need to re-think what you're trying to achieve.

    Now that I've nearly written a book on this, if you have questions, throw them out.
     
  4. zakk

    zakk 1/2 ton status

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    and THAT, ladies and gentleman, is why i call him DR. WATSON!!! /forums/images/graemlins/thumb.gif

    wow. info overdose...going back for second reading of your disertation /forums/images/graemlins/cool.gif


    **EDIT**

    Ok, now that i have read and understood at a basic level, i want to run my idea by you Dr. Watson:

    I have a Springer Suspension and obviously want to maximize my set up. I was thinking of using a set up like this:

    [​IMG]

    What are your comments on a set up like this? IMHO, it is still pretty far out, and you could angle them slightly to get them closer to the tires. I have a set of the new rancho RS99036's with 15" of travel.

    thanks! /forums/images/graemlins/thumb.gif
     
  5. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    I'd have to say that's a pretty ideal setup for a stock body vehicle, and really clean too. The tires often rub the vertical surface of the fenderwell so you really can't go outside of that. Mounting the bottom of the shock closer to the wheel would help but at that point you may have to notch the fenderwell for clearance. I'm sure the bottom mount of that shock is on the ubolt plate so it's directly above the spring which is why it's sticking through the floor so far. If it was dropped down lower on the tube you'd have much less shock in the interior.
     
  6. zakk

    zakk 1/2 ton status

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    thank you for your comments. Do you think it is better to have it on top of the u-bolt plate? or on the tube?

    Thank you again! /forums/images/graemlins/thumb.gif
     
  7. Desert Rat

    Desert Rat Fetch the comfy chair

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    Excellent information Stephen. I have a question. Given that the severely angled inboard shock setup will give me grief on body roll, I want to keep my shocks as far outboard as I can. But I am in a dilemma. My rear driver side mount has cracks in the bracket and my passenger side mount hole has several cracks radiating out from it. Now, I could simply weld them up given my recent purchase of a Millermatic 175. However, I was considering relocating the shocks using a crossmember setup like many have done. But, I want to keep them much farther outboard than others have. This will effect the length of the shock which could be a problem. I would also lose the benefit you describe of the stock setup of having one forward and one rear. Would a possible solution be to fabricate two crossmembers, one installed forward and one rear? Then I could maintain a forward angled shock and a rearward angled shock. Or, should I simply install kicker shocks to reduce axle wrap and just mount the shocks to a single crossmember? Or perhaps two crossmembers with four shocks, 2 forward and 2 aft? Anyone find a good compromise that elminates the stock mounts while keeping body roll to a minimum?
     
  8. zakk

    zakk 1/2 ton status

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    Running them through the bed.

    If you have a body lift, some have used F-150 shock towers in the rear. If you do not go inboard as much as possible, you will not be able to use the 9012's or 99036's or atleast not in a way i have seen. Dr. Watson would be a better help than I.

    the dual crossmembers could work, but they would have to extend outside the frame rail to mount them in a "factory" like position. Maybe make the angle a bit more and use the f-150 shock towers, as mentioned previously.
     
  9. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    You might be able to look at mounting them near the stock location but not actually use the stock mounts. Or repair the stock mounts and brace up the outside of the shock. One of the most effective mounts we've done on a stock body vehicle was actually outside the spring and outside the frame. But the truck had a wide rear axle so the tire wasn't close to the spring.
    I'd look at the wrap damping as a secondary concern, since we have a lot of packaging problems already.
     

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