There are two ways to look at this.
1) Lose 100lbs./inch
2) (Capacity x LC)/new lc

Now, which formula do you think many operators will find easier to figure out? Load center gets removed by 6"=600lbs. lost, from 5000=4400lbs. The guys I train even freak at these simple formulas, nevermind having them figure out 5000x24, divided by 30= HUH?

The usual "de-rating" formula is; A truck with a 4000lb capacity @24" load centre is lifting a load with a 30" load centre -
Multiply 4000x24 (our capacity x load centre) =9600. Divide 9600 by new load centre (30) = 3200lbs our new capacity

Thanks for the info, this helps to clarify the issue as most people only talk about counter balance load centers.

I ran across a salesman that had a factory downrating graph fo the specific model that allowed me to see when I should consult the factory for a revised spec plate.

IMPORTANT NOTE: As previously stated these caculations should only be applied to situations where the load is not being handled at anywhere near full height as their are other factors that need to be considered near full height including side stability, the fact that the floor may not be flat and level (a slope of up to 2% is allowed), et cetera.

Firstly you need to read and reflect on all the issues mentioned above in respect of counterbalance forklifts, and take heed of advice about getting a rerating from the manufacturer because ratings are complex.

For a reach truck you need to measure the load distance L from the outrigger wheel centres to the rated load centre with the forks fully extended - the overturning moment related to the load is then the rated load by L.

Then determine the new distance L distance = L1 at 30 or 36 inches load centre.

The adjusted load is then the RL * L / L1.

As an example a Clark NPR 22 is a single stroke reach truck and has a rated load of 2000 kg at 24 inches. The distance from the load centre to the centre of the outrigger wheels when the forks are fully extended is 28.6 in.

For a 30 in load centre that distance becomes 34.6 ins and the rated load = 2000*28.6/34.6 ~= 1650 kg.

And for a 36 in load centre that distance becomes 40.6 ins and the rated load = 2000*28.6/40.6 ~= 1400 kg.

Similarly for a Clark NPR 15 D, a double stroke reach truck (and because of the greater fork extension has a lower rating even though the reach truck is heavier) has a rated load of 1350 kg at 24 inches. The distance from the load centre to the centre of the outrigger wheels when the forks are fully extended is 50.67 in.

For a 30 in load centre that distance becomes 56.67 ins and the rated load = 1350*50.67/56.67 ~= 1200 kg.

And for a 36 in load centre that distance becomes 62.67 ins and the rated load = 1350*50.67/62.67 ~= 1090 kg.

Does anyone know the formula to calculate the downrating on a 30-36 inch load center for a reach truck? I would apreciate your help.

Sorry, I forgot. Go to rightline dot com and you will find one.

Most of the attachment manufacturers have easy to use online capacity calculators. You just plug in the numbers. I've used them all and they all come out the same. Go to www.rightline.com and there is one right on the home page. I use it a lot and it is pretty accurate.

You can roughly do it in your head, 2000x24 divided by 78.This gives a slightly lower number than the true capacity.You should always work on the capacity at the maximum lift height.This also gives a safety margin.

Johnr-j is correct in his advice.

However if you are only going to carry the load at a low height - that is much lower than the maximum lift of the mast - then the formula is as follows:

Rated load x (rated distance plus the distance from the fork face to the centre of the drive axle) = modified rating x (modified distance plus the distance from the fork face to the centre of the drive axle).

For example a 2000 kg @ 24 in forklift plus 16 in from fork face to centre of drive axle would have a revised rating of 2000 x (24 + 16) = revised rating x ( 78 + 16) giving a rating of 850 kg.

Note that this revised rating includes the effect of the carpet prong on stability. Assuming the prong is supported on the forks, and the prong weighs 100 kg then conservatively the device can carry a roll of carpet 850 - 100 = 750 kg.

It is still recommended that the manufacturer be contacted re a new rating as they can give the rating at full mast height.

There are many factors that determine the rated capacity of any lift trucks beyond simple mathematical calculations of inch pound ratings, etc., etc. Other factors that determine the capacity are:

1. Amount of mast tilt
2. Physical limits of: a.) mast & carriage bearings b). Tilt cylinder strength, c.) Tire compounds & tire sizes d.) fork section (W &T) as well as length. & type (std. taper or full taper) used, e.) limitations of any attachment, f.) lift cylinder column strength.

Best advise let the manufacturer do the work & the lawyers won't get more $$$$.

4 metre carpet boom.......LC now 78"
Truck rated capacity 2000lbs@24"

LC extended by 54"

reduce capacity 100lbs/per inch.....5400lbs

Its only a 2000lbs rated truck to start with!

A fork truck is basically a ratio & proportion machine. Therefore , I don't see the formula you offer working very well. It can reasonable be said that each time you double the Load Center the capacity is reduced by about 50%. This is not perfect, but, it is close enough for rough calculations. One must also take into consideration the extra weight of any special forks or attachment above the weight of normal forks. As said above, this is not perfect but it will help you from making a gross capacity error.