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Jumping your truck

Discussion in 'Center Of Gravity' started by Paxx, Nov 25, 2004.

  1. Paxx

    Paxx 1/2 ton status

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    I did a search and got into posts from over a year ago without finding any good info so I thought I would start a thread.

    I am interested in knowing what it would take to safely jump a leaf sprung truck without mass carnage ensuing. Off the top of my head I can think of the basics such as trussing axles, good bumpstops, limiting straps, quality springs, sturdy shock mounts, and good shocks but is there anything else? I'm sure that I haven't thought of everything.

    I do not plan on regularily jumping the truck or going abnormally huge off of big jumps but I have had the truck completely airborn before and can forsee it happening again, as well as it is quite common to have the front end jump up in the air a few feet getting throttle happy "bumping" up small ledges etc. I just want the piece of mind knowing that I am somewhat prepared and that the truck leaving the ground does not signal the death of my rig.

    Thanks
    ~Max
     
  2. zcarczar

    zcarczar 1/2 ton status

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    You need to make sure the frame is also properly braced. I know my frame is trashed due to blasting through the desert and jumping my blazer.

    Hydraulic or Air bumpstops dont hurt either, they are basically a progressive rate bump that gets a lot stiffer as it compresses.

    Don't forget about making sure your driveshafts are in top condition, cause if your shafts are too short and you driveshaft falls apart in mid air its bad [censored] cause it will kill your truck on landing.

    Dont forget that unsprung weight is a bad thing. That is all the weight not sprung by the springs, stuff like this is axles, tires and wheels.
     
  3. ntsqd

    ntsqd 1/2 ton status

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    First you need a cage that not only protects you, but also picks up the landing loads and distributes them thru-out the whole vehicle.
    Well gusseted hard points (damper mounts, spring mounts, etc.) are crucial and the cage should tie into all of them. So are good bumpstops. I've yet to see a urethane bumpstop work well and live. The darling of the older Class 8 dezert trucks is the rubber bump found on first gen Pathfinders. They're figure 8 shaped and appearently work very well.

    If you've got the $$ for them you can not beat going to Hydro-bumps, but these should not be the final limiter. The truck should also have normal bumpstops on it, but they can then be of the small pad variety rather than a big block. Figure $150 per corner and up for hydro-bumps. Search "Marvin Shaw" for the maker of the most affordable hydro-bumps.
    Here's one shot of a King Hydro-Bump. The shaft is fully retracted (not charged with Nitrogen) otherwise it would stick down 6"-8" from the blue ano'd sleave.

    See if this link doesn't take you to the "Skunk Works" page on rdc. Each thread is a photo essay on a dez racing vehicle.

    As a side note, here's a really nice '68
     
  4. Paxx

    Paxx 1/2 ton status

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    So for example, say the family cage design that is so popular nowadays ie. Steve Fox's, would this type of cage give the distributing qualities that I would be looking for or will the design be different.

    I am set on using a family cage because I quite often bring passengers with me. Not that I would do much jumping with passengers because of the weight issue but for the other types of wheeling it would be necessary.
     
  5. Paxx

    Paxx 1/2 ton status

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    zcarczar - Have you done any of this highspeed desert type stuff since you did the 52" swap? I am curious how the longer springs would handle it. I know that some of the desert racers I have looked at use up to 63's in the rear but are they stiffer than what we use?
     
  6. bablazer73

    bablazer73 1/2 ton status

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    The cage is a good idea anyways.
    I did some jumps with my old 76, and it bent/tore the frame on the drivers side, just in front of the front spring shackle. On the 73, we boxed that section of the frame and ran an extra plate on the outside. I have heard from other people that this is a weak area.
     
  7. ntsqd

    ntsqd 1/2 ton status

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    I haven't seen Fox's cage so I can't comment on it.
    Typically 'Family Cages' are designed only for roll over protection and not load distribution. A load distributing cage has a LOT more tubing in it. It includes an engine cage that is part of the whole structure and is not just a pair of shock hoops. At the extreme things like radiator(s), shocks, bumpers, spare tire(s), etc. are also mounted to it.
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    And that extra tubing is primarily for additional triangulation to transfer suspension loads into a "space frame" type of cage. Remember, rectangles can "diamond" with loads at the vertices where as triangles are will hold shape and transfer the load. As already said, distributing the forces evenly is the primary concern.

    And of course jumping implies higher speeds and a MUCH greater likelihood of multiple rolls and high load impacts, so a cage is much more important for safety. This is where you move into better alloys, processes, and a very high degree of structural design. Much different than the rock crawling or trail running world…
     
  9. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    zcarczar - Have you done any of this highspeed desert type stuff since you did the 52" swap? I am curious how the longer springs would handle it. I know that some of the desert racers I have looked at use up to 63's in the rear but are they stiffer than what we use?

    [/ QUOTE ]

    You have to tune the shocks to properly control the spring movement. This is why it is important to invest in quality shocks. You really can't buy a shock off the shelf and expect it to do it's job properly when you start using a vehicle in such an extreme manner. Even the experienced race teams are always messing with the shocks so the suspension acts properly.
     
  10. Paxx

    Paxx 1/2 ton status

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    How difficult is it to tune the higher end shocks? Say I had my set-up dialed in for rockcrawling but was heading to the dunes, what would it take to change it up? I know that most of the high end shocks out there don't have a dial like the new rancho's etc.
     
  11. Paxx

    Paxx 1/2 ton status

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    Also, how much extra weight are we talking in the cage? It's gonna be heavy enough anyways and the thought of going nuts with more tubing seems like it would be going backwards in the flying department. /forums/images/graemlins/deal.gif
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    [ QUOTE ]
    Also, how much extra weight are we talking in the cage? It's gonna be heavy enough anyways and the thought of going nuts with more tubing seems like it would be going backwards in the flying department. /forums/images/graemlins/deal.gif

    [/ QUOTE ]
    That's where alloy and size selection come into play. Since most of the extra pieces are not intended to take impacts, and they should have no bending loads if set up properly, they can be smaller diameter and thinner wall. Even small, (relatively) thin wall, common 1010 HREW tube is VERY strong when loads are applied along the length of the tube. It's the bending strength that really suffers. And the extra supports can help eliminate unsupported spans, so some of the perimeter tubes might be made smaller too when they don't need to support weight on a span "in bending".

    And for those who really want to air it out, the cages aren't really made to take impacts at all without deformation. Basically, "use once" disposable cages. They might be cut an pieced for a minor bump or two, but one good roll and it's pretty much done. A cage can be made much lighter and still stay safe if you don't want it to survive a few rolls before rebuilding it. The problem comes in for a multipurpose rig that rock crawls and does the high speed stuff, and is expected to survive a few seasons in spite of hard use.
     
  13. ntsqd

    ntsqd 1/2 ton status

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    [ QUOTE ]
    How difficult is it to tune the higher end shocks? Say I had my set-up dialed in for rockcrawling but was heading to the dunes, what would it take to change it up? I know that most of the high end shocks out there don't have a dial like the new rancho's etc.

    [/ QUOTE ]

    I'd be surprised if many could tell the difference btwn dampers dialed in for krawling and those dialed in for high speed stuff while krawling. The other way around would not hold true. Dial them in for the speed stuff and then krawl them. I'm betting the difference is not worth trying to change unless you are competing - and maybe not even then.
     
  14. Paxx

    Paxx 1/2 ton status

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    Ok so I can use long springs as long as the proper dampening is there, how about rear shackle flip? Will this cause any negative effects or would it be safe?

    Also what shocks would you choose. I expect them to be probably $200-$300 each so I want to make sure I get the right ones. Are there any major differences I should be aware of between the shocks in this range?
     
  15. 85mudblazin

    85mudblazin 1/2 ton status

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    why not just go coils?? by the time you spend all the money for dampening with the leaf springs I bet you could just go coils, just a thought /forums/images/graemlins/thumb.gif
     
  16. Paxx

    Paxx 1/2 ton status

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    Just because of how much easier leaves are to work with. I understand how they work and how to set them up but all that 4 link crap has my head spinning. I would have to pay someone to set it up for me as well which I don't like the idea of. I also think they are a bit less likely to leave you stranded if damaged. /forums/images/graemlins/dunno.gif

    I'd like my build to be simple, functional, and stout. /forums/images/graemlins/waytogo.gif
     
  17. Paxx

    Paxx 1/2 ton status

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    Oh and one more thing for the shocks, will they make up for the lack of a sway-bar?

    And as long as I'm not missing anything the standard anti-wrap bars such as the a-tron etc. should work just fine right?
     
  18. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    Ok so I can use long springs as long as the proper dampening is there, how about rear shackle flip? Will this cause any negative effects or would it be safe?

    Also what shocks would you choose. I expect them to be probably $200-$300 each so I want to make sure I get the right ones. Are there any major differences I should be aware of between the shocks in this range?

    [/ QUOTE ]

    Scroll down a little bit.

    Those look like they may bring bling to the ring........................ /forums/images/graemlins/screwy.gif
     
  19. ntsqd

    ntsqd 1/2 ton status

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    [ QUOTE ]
    why not just go coils?? by the time you spend all the money for dampening with the leaf springs I bet you could just go coils, just a thought /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Leaf Springs have internal damping built-in. If look at the damping rates for coils vs leaves you'll see that the coils need more damping. The very internal friction of leaves that makes them not ride as nice as coils works to dampen them.

    Interesting Fox's there, BRB. Put a metering valve on the displaced fluid. Wouldn't have thot there'd be enough volume movement to have a large effect.
     
  20. Paxx

    Paxx 1/2 ton status

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    Hmm, travel length could come into play when selecting shocks. How much travel would you want for a 63" rear spring? I would most likely run the shock through the floor and down to the top of the spring perch unless there is any reason to mount it somewhere else. I'm assuming straight up and down is best.

    I would guess at least a 16" travel if not 18". What do you guys think?
     

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