When I worked for ITSSAR, I came across the pivot-steer truck for the first time and I tried to interpret the stability triangle theory to the truck, and expressed my doubts as to stability to George Coates, then Director General of BITA. He later claimed that I had ruined his Christmas as he played with two triangles of card on the dining room table to try to understand the issue.
The main problem is alignment of the fork arms when entering a load or picking a load from a rack cell, particularly at height. This is confused when normal instruction is that a truck should be positioned for a straight entry or load destack before using the hydraulics to maintain maximum stability, yet the pivot steer design means that steering is necessary in both stacking and de-stacking manoeuvres.
The perceived method for stacking with a pivot steer truck is to position the truck to the opposite side of the aisle, stop and rotate the mast in the aisle. Then, move forward and reduce the steering lock to maintain the load in a straight entry into the cell.
The reverse is true when de-stacking. Here, however, the fork arms enter the load and need to be steered in by reducing steering lock as you go in, straightening the truck. Once in position and with the load lifted, steering lock has to be reapplied as you extract the load. However, the problem is that the far corner of the load is invisible to the operator, and side shift might need to be applied to ensure that that outer corner of the load remains clear of the cell uprights. This effect may be magnified as rear tilt may be limited, particularly on higher-lift masts. The effect of this is to finish the extraction with the truck on full lock. To maintain maximum stability, the truck should be stopped while the steering is returned to the straight-ahead position. Once that has been completed, the load may then be lowered to a safe travelling position. This means that the load is turned when it is raised, but this may be necessary to ensure that the load can be lowered completely clear of any lower obstruction.
One aspect of stability on a pivot-steer truck is that the counterweight and battery pack are often heavier and set further back and lower than in a conventional counterbalanced truck, thereby increasing the counterbalance effect.
I have seen some scary moments with pivot-steer trucks, but I do have an operator certificate having received training on both main types available at the time (Bendi and Flexi). I was responsible for BITA classifying the truck as a separate type, for ITSSAR developing a separate test and I wrote the original RTITB Trainer's Guide. It is now several years since my operator's certificate was refreshed as I have no further need of it, being retired.