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Gas Tank in front of rear axle???

Discussion in 'Center Of Gravity' started by Greg72, Dec 14, 2003.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I did a little calculating, and I can build custom tank that follows the lower profile of the frame and that gives me about 40 gallons of capacity.

    The tank would basically start where the rear t-case output is (so the tank will need a U-shaped cutout to provide driveshaft clearance) and the tank will extend to about where the 14BFF yoke is...


    So here's my REAL question:

    Moving the tank will provide an obvious departure angle improvement, but it is also moving about 240Lbs (when full) from behind the axle, to a position BETWEEN the axles.

    It seems like it would help provide better balance, but it IS shifting the front/rear weight bias around. Any insights about whether this is a step in the right direction or not???


    /forums/images/graemlins/thinking.gif
     
  2. sled_dog

    sled_dog 1 ton status

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    I've been wondering the samething, I removed my tank from the back and was planning on placing it where you are talking about. I've just been hoping it won't mess with the weight but I don't know.
     
  3. Sandman

    Sandman 3/4 ton status Author

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    I have looked at the same thing. I think moving the weight forward would be a huge improvement in climbing abilities. Bqasically it would move the center of gravity forward in a front to rear perspective. I have also considered cutting a hole in the floor behind the seats, dropping the stock gas tank into it and then building a cover over the top. The only concern would be the driveshaft concern but a loop could solve that issue.
     
  4. juanblzer

    juanblzer 1/2 ton status

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    I'm also looking at this but I want my custom cell to be no deeper than the frame rails to the floor.
    I'ts been a while...
    How does one calculate volume for a fuel cell?
    Base X Height X3?
     
  5. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    I'm also looking at this but I want my custom cell to be no deeper than the frame rails to the floor.
    I'ts been a while...
    How does one calculate volume for a fuel cell?
    Base X Height X3?

    [/ QUOTE ]


    L × pi × r^2


    Once you have the total cubic inches....divide by 231 to get the gallons.

    1 Gallon = 231 Cu in


    /forums/images/graemlins/cool.gif
     
  6. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    It's a bit more complicated than must moving weight. Having it located behind the axle actually multiplies the weight on the rear axle and reduces it on the front. So, as a WAG, a 240 lb tank in the stock location might add 260 lbs to the rear axle and reduce 20 lbs from the front axle due to leverage.

    As for exactly what that means for any given truck, as usual, that depends... Lots of things to consider, mostly what weight bias you started with. My truggy is so light in the back, doing what you propose would likely have a dramatic negative effect on performance for me. With a full bodied K5 with lots of gear in the rear (like theRobzilla) would be less affected.

    Remember, you can move the trank forward some without going in front if you have enough lift. That’s effectively what I did when I put the K5 tank in my K30 frame. But I also added a bumpstop to keep the axle out of the tank.

    I hope to soon add rear links in the rear so I will need to build a tank for my truggy to clear the suspension. But, but it will keep as much weight to the rear as possible.
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    [ QUOTE ]
    L × pi × r^2

    [/ QUOTE ]
    That's assuming a cylindrical tank. For a standard square cell it's simply:

    L x W x H = V
     
  8. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    i plan on doing this sometime soon also. AFA balance goes, seems to me that when full or close to it the gas tank being in the far back of the rig would help counter balance the heavy winch/engine/tranny etc that is up front.. but moving it to the middle ya arent gonna have much weight at all in the rear of your rig. I dont think its a problem necessarily, just something to add to the calculations when buying rear springs and driving down steep grades. /forums/images/graemlins/wink.gif

    j
     
  9. Triaged

    Triaged 1/2 ton status

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    From a vehicle dynamics standpoint the tank should be at the CG. That way you won't have the balance of the car changing as the tank empties. Shifting around 240# of weight is a large amount but with a truck you also have to figure in all the crap you have in the back. I think moving the tank forward would be a good thing to do but other stuff (like dual batteries and whatever else can be moved) should be moved to the back to help balance it out. For me I have been thinking of a comprimise of keeping the tank in the back just a bit below the frame (I have no body lift) with 2 kickers going forward along the driveshaft to be able to get the volume up. I think alot of the vehicle dynamics crap goes out the window with a truck /forums/images/graemlins/crazy.gif The balance will never be too good...and corners will almost never be taken "at the limit". One other thing to worry about is it you will be able to work on the drivetrain with all that gas tank around it?
     
  10. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I just finished my rear tank and am about to begin construction of the mid tank. Just like you said in front of the axle is where my mid tank will be. Wouldn't all of the weight of the tank in the rear be removing weight from the front bias and adding to the rear? Kinda like a teeter totter setup. Our rigs are already front heavy. Is there a computer program out there that will figure weight percentages front to rear by pluging in locations of components or something like that. Go weigh in and get a baseline and then you can move some weight from here to there and see where the percentages went?
     
  11. az-k5

    az-k5 1/2 ton status

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    Also keep in mind that as the takk empties new center of weight will lack most of it's positive qualities. You can always slope the tank so the fuel is more often in a given location. Rake it down if you want the weight towards the middle/front or rake it up if you want the weight to stay right above the axle.
     
  12. TONYP

    TONYP 1/2 ton status

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    Greg, with the tank always changing weight from full to empty I don't think it would be a concern, think about if you have people or gear in your rig and what thats doing to the balance of things...If you have your rocker boxes out I have two side tanks that bolt up in there, I could get you the dim. from then and you could put them on the sides...then add fuel doors to both sides...

    [​IMG]
     
  13. 77ChevyK10

    77ChevyK10 1/2 ton status

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    i put a 31 gallon K5 tank in my k10 and it is centered over the axle. but it sits on the top of the frame rails the bottom is not lower then the frame at all.
     
  14. crwln73

    crwln73 1/2 ton status

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    I havent noticed any problems in weight transfer.I did baffle the interior of the Fuel cell with two baffles that go side to side to prevent fuel slosh.My biggest problem is fuel starvation when on extreme upward inclines.I do have a 1gal.sump in the front of the tank.Im thinking of putting another fuel line feed in the rear of the tank.
     
  15. DaveCowley

    DaveCowley 1/2 ton status

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    I moved my stock tank to up there but just cut a hole in my floor so it sits just slightly higher than what you are talking about but is in the same location and I climb better than most rigs but I have eliminated a whole lot of other weight too so who knows but my K5 was the only full bodied one to climb the rock pile at BB03 so it seems to work ok. I don't notice it being really dumpy on downhills but I am not too proud of being able to go down something. I'd rather say I could go up it. It is just what you are building it for right. I don't really think you could lose with that location though.
     
  16. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I think Gregs idea won't work too well given the fact that he is moving the entire engine/trans/T-case forward 5" from stock. /forums/images/graemlins/ooo.gif Also he is raising the whole set-up as well about 2" I think.
     
  17. chvyhs

    chvyhs 1/2 ton status

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    I don't see any problem with it. Like someone else said "it would be like driving around with an empty tank. Also, think about a pick up with saddle tanks. All of that weight is in the center of the vehicle regardless of whether the bed is loaded or unloaded.
     
  18. unclematty

    unclematty 1/2 ton status

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    I read through the thread amd it spounds like someof you have allready done the move your tank thing, my?? is can i move my stock tank straight up to the floor of the body,? I hava 3 inchbody lift,looks like there is plenty of room to make the move, I just want the pro's and con's of this before I go and rip the (darn) out of the blazer. /forums/images/graemlins/thinking.gif /forums/images/graemlins/whistling.gif
     
  19. sled_dog

    sled_dog 1 ton status

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    you could do it. I was planning to but without the body lift I would have been hitting crossmembers so I just went with a smaller fuel cell. Advantages, uh gets the gas tank out of the way of rocks, thats about the only one I see. Moves the center of gravity up, all be it how much who knows but it still will. Lose cargo space.
     
  20. unclematty

    unclematty 1/2 ton status

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    exactly what Iwas thinking, thanx! /forums/images/graemlins/waytogo.gif
     

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