Hi all

Pity you can't put diagrams on here.

There are a limited numbers of concepts trainees need to understand:
Firstly there is the seesaw concept where the seesaw fulcrum is the drive axle of a counterbalance forklift - the relevant distance is the rated distance plus the extra distance to the drive axle - if you double that distance then you have to halve the load. For example if the forklift has a 24" load centre and a 16" distance from the fork face to the drive axle the relevant distance is 40'. Doubling that to 80" halves the rating with the load centre than being 80 - 16 = 64" from the fork face.

Secondly there is consideration of the forks themselves. I have nothing in writing from any fork manufacturer but have evidence to support that forks fitted to forklifts are often, or maybe rated higher than the forklift, and that forklifts rated individually at a certain rating may be downgraded as a pair presumable to allow for the fact that loads are supported offcentre be typically 30 mm on average. Hence a pair of forks individually rated to 4000 kg at 24" may be rated as a pair at 7500 kg at 24" and may be fitted to a forklift rated at 7000 kg at 24" (this is the actual situation in an investigation I am involved with into a case where two forks failed completely and concurrently at the heel after three years use). For forks the allowable load halves as the distance from the fork face doubles. So in the case above the load centre goes from 24" to 64" and hence the allowable load on the forks is reduced to 24/64 = 37.5% of its rating at 24" or a little more than a third of the forks original rating.

Thirdly there is consideration of any attachment being used, its rating with load distance, and the impact its weight and the degree to which it alters the actual load distance affects the forklifts rating. For example fitting a third party side shift adds weight and usually also means the forks are further from the drive axle so the two factors combine to reduce capacity.

Finally there is the serious matter of side stability. No forklift manufacturer I'm aware of provides customers with information as to whether side stability(rollover) or forward stability (tipover) is the controlling factor in rating the forklift. If it is side stability that is the issue then in rare situations all the calculations above may be irrelevant when the forklift is being operated at or close to maximum height.

So my advice is and always will be that the manufacturer should be invovled in determining the capacity of the forklift at different load centres and/or with different attachments. Every forklift should be fitted with a laminated chart that shows the actual capacity versus attachment and load centres for all situations likely to be encountered in the workplace, that all loads have mass estimates shown on them, and that at least one forklift (preferably the largest or one of the larger ones) is fitted with a load measuring device so that where the weight is not known that forklift can weigh the item to determine which forklifts can safely handle that item.