Holden VF, WN accessory Installation Manual has the install instructions for the genuine superlift shock absorbers under chapeter 5. Within this section, the instructions recommend to always have a
minimum of 100kpa (14.5 psi) at all times (unstated but its to avoid damaging the air bladders).
Since there is also the choice of 1600kg or 2100kg towbars listed within the Accessory installation manual, i guess there would be different recommended ball and draw weight depending on the towbar package installed. Adding to confusion, Holden also made available a 1200kgs tow option which is likely still available from some dealers. In all cases, the maximum weight of an unbraked trailer is max 750kg.
Note that the
ball weight is taken as being between
5% to 10% of the total trailer weight but is limited by the towbar design which should list a max ball weight and trailer weight on the towbar compliance label stuck to the drivers b-pillar.
Again, note that the ball weight must be subracted from all the weight of the passenger and the weight of accessories and luggage that is loaded into a vehicle. All this crap must not
exceed the axle load. A sedan has a 1300kg max rear axle load and the only way to really check axle load is to go to a weighbridge. Everyone who tows big things in loaded cars should go to a weighbridge at least once if not twice.
So I'd guess the ball weight (actually the total axle load) would have a direct impact on the pressure needed to level the vehicle while any superlift maximum pressures specified would be related to the safe maximum working pressure before blowing up the bladders. You will be somewhere between these minimum and maximum limits if things aren't out of kilter.
Obviouslyit's a given that you need to stay within all weight restrictions (GVM, tow ball weight, axle weight, etc). Then you'd simply pump up your shocks until the vehicle and trailer are level. The resulting shock pressure should be somewhere between the recommended minimum and maximum shock pressure.
Why you were given two maximum pressures, who knows, but as the shocks are genuine Holden superlift shocks, first ask your installer for some supporting documentation to clarify the air shock lable 1030kpa (150psi) and vehicle owners manual 620kpa (90psi) discrepancy. If not joy, ring and ask the same from HCC.
If you haven't towed big rigs and plan to do such, go do a course or be prepared to be pushed around and have the smelly stuffing scared out of you.
