Forklift capacity at various load centers
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  1. #1
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    Default Forklift capacity at various load centers

    Everybody knows that forklifts are rated for X lbs at X from the face of the forks, but what do you do if you are outside those parameters? My standard equation has always been to figure the forklift rated capacity distance from center of front wheel. Then divide the rated distance from the center of front wheel by the distance of the load you want to pick. Then multiply that number by rated capacity.

    For example, our Hoist 60/80 is rated at 80,000 lbs at 36” load center. The distance from the center of the front wheels to the 36” from fork face is 69”. If I wanted to find out the capacity at 48” I would do this-
    69+12=81
    69/81=.852
    .852 X 80,000=68,160

    Luckily, I have the load chart for this particular lift, all the way out to 72”, and the 68,160 number is awfully close to the factory load chart.

    The problem I’ve ran into is other calculators and formulas for figuring this that I’ve found on the web. These sites say I’m wrong. They say you should just divide the rated load distance by the actual load distance, then multiply that number by the rated capacity. Using the same figures above, it would go like this-
    36/48=.75
    .75 X 80,000=60,000
    This is vastly different from the factory load chart that I have. Like I said, I have a factory load chart, all the way out to the tip of the forks, for the 60/80, but I need to know that I’m figuring it right for other lifts that only have the one rating at a certain distance.

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    I use allowable moment at the apron. 80k @ 36" would be 240,000ft-lb.

    69" is 5.75', so 240k/5.75= ~41,800lbs.

    This is very conservative, it makes no accommodation for elements of each exact lift truck.

    Also, you cannot move backwards from the stated capacity and expect the capacity to increase beyond the rated lift. IE- you cannot observe this lift to do 80k @3' and then expect it to do 160k at 1.5'.
    Last edited by Cole2534; 04-20-2020 at 03:14 PM. Reason: because zeros are important

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    It depends on the failure mode. You're calculation is correct for tipping. The more conservative (i.e. 36/48 style) is going to be better if the limiting factor is bending moment at the fork root (e.g. fork bending or the rollers).

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    I suspect most online calculators are so conservative as to avoid liability. I just wanted to make sure I was doing it right with my calculations.

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    height of load can effect capacity. and steering ability is a concern. many a person going fast and trying to turn fast have
    .
    1) tipping problems
    2) steering not responding cause back wheel lightly loaded (this often a problem before near max lifting load)
    3) heavy inertia loads resisting sudden direction changes
    .
    ..... and raising load if rear wheel goes up in air and you lower load fast than truck rear wheel comes down fast. get a bit of whip lash and most fork trucks dont have much shock absorbing ability (truck not suppose to bounce on springs or soft tires)

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    Common youtube failure mode is lowering a load close to capacity when the mast is tilted back. As the load comes down it also moves away from the lift CG and things get ugly.

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    Quote Originally Posted by tomjelly View Post
    Common youtube failure mode is lowering a load close to capacity when the mast is tilted back. As the load comes down it also moves away from the lift CG and things get ugly.
    Yeah, most the times I needed to check my shorts was trying to set something down that was too heavy, but easy to pick off a deck over trailer.


    Sent from my SM-N960U using Tapatalk

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    Quote Originally Posted by tomjelly View Post
    Common youtube failure mode is lowering a load close to capacity when the mast is tilted back. As the load comes down it also moves away from the lift CG and things get ugly.
    If you know that's an issue like you are close to the ragged edge via numbers, one can block the lower channels of the mast with steel or hardwood.

    That puts the pivot point 12-16" farther toward the load and you'll be able to be stable.

    That doesn't get it moving forward but there's opportunity to use skates or rollers, or pallet jack to assist on the outboard end.

    I knew I was close with my Fadal VMC on the goose with a 7k forklift, due to the distancing required by the machine's splash guarding so I setup to use the blocking to prevent a bad day. In the end I didn't need it, there's some additional counterweight that's "undocumented". Verified with other machines known to pass 9k.

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    Quote Originally Posted by DanielG View Post
    It depends on the failure mode. You're calculation is correct for tipping. The more conservative (i.e. 36/48 style) is going to be better if the limiting factor is bending moment at the fork root (e.g. fork bending or the rollers).
    Well, I would submit that the load is the same on mast, regardless of the weight on the forks, if the back wheels are off the ground. In other words, if you have a 5,000 lb load at 24” center and it raises the back wheels, and you can also raise the back wheels with 4,000 lb at 36” center, the mast is seeing the same load on both. The counterweight is the limiting factor, and you can’t put more weight on the mast or front axle than the counterweight can counterbalance.


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