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Thread: Spring rates

  1. #1
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

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    We all know that these trucks are rated at 5/4 ton. That means that the rated payload for these trucks is 2,500 lbs (cross-country, we're allowed 3,000 lbs highway)

    Spring rate? This is the rate of deflection per amount of load. It is expressed as lb/inch (how may pounds of loading will it take to deflect the spring 1 inch)

    Our front springs are rated at 515 lb/in.

    The rear springs are rated at 715 lb/in (cool, huh?)

    Here's the good part - (515 x2)+(715X2)=2,460
    Now, Payload/2,460 = 1.02 inch = the amount of total "squat" the truck would experience at rated cross-country payload capacity!
    Even at the rated highway laod capacity of 3,000 lbs, the truck would only squat 1.22 inch!

    Thus, if you load an M715 with stock suspension to the point of visible squat - you're probably overloaded.

  2. #2

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    and here's the bad part: your back will feel all of that capacity!

    that is pretty cool about the rear rate. Here's a question. Are those spring rates the rate of the unloaded spring, or the rate of the spring w/the weight of the truck on them?
    **I heart Bump_r **

  3. #3

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    with over 4000 lbs in mine it rode VERY smooth.

  4. #4
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

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    That is the rating of the spring. Likely as manufactured. Leaf springs a naturally progressive (the farther you get into their "travel", the stiffer they get), thus the "real" rates are slightly higher than the theoretical in the original post. I don't have the rate curve handy, but we may be able to come close if we really wanted to pick nits. Gunk between leaves, and in shackles will add to he ride stiffnes, too. A lot of variables, here.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  5. #5

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    so you're saying that the springs are built to carry the weight of the truck as the starting point, and then they factor in payload? If not, those rates would be just enough to hold the truck off the axles.

    suntin ain't clear ta me
    **I heart Bump_r **

  6. #6
    Join Date
    Dec 2003
    Location
    West-central Ohio
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    The capacity of the springs is unknown. The deflection of them is the topic of discussion. The gross weight rating of the truck will be significanly less than the capacity of the springs. At GVW, the springs are "squatted" an inch. Driving down the road, the inputs will GREATLY exceed the static loading, hence wheel travel.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  7. #7

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    "Here's the good part - (515 x2)+(715X2)=2,460 "

    If that's the rated capacity of the springs, period, it won't be enough to carry the 6,000lb truck PLUS the 2500lb payload. See what I'm getting at? I understand what you mean in your post. I think they must factor in the weight of the truck FIRST ie, that 715lb rate is in addition to whatever it takes to hold the truck up. Make sense? lol..
    **I heart Bump_r **

  8. #8
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

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    I'll say this one more time. At the 2460 lb laoding, the springs will deflect an inch. If you laod it htat much again, they will (theoretically) deflect another inch. The springs will accept a huge load before failure, maybe more than the gross weight of the truck. We just don't know. The whole issue at hand is spring RATE as in rate of deflection, not RATING as in "how much they can hold" Get your head around the difference and it'll make a ton more sense.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  9. #9

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    well i have a picture of mine with 4000+ pounds in it. i took a picture of the bump stop to axle on level ground..... its on, or was on my site

  10. #10
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

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    I've hauled 5300# of crushed limestone aggregate (gravel), myself. There is not an issue of capability of the truck or the suspension to haul loads in excess of the rated capacity. The entire dissertation was over deflection of the springs at a given load. NOT what is the absolute maximum these things can haul.

    If your truk squats more than an inch or so, your springs are shot or you are overloaded. Period.

    Those that will get it got it, those who haven't just won't.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

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