Curb weight is an irrelevant number, interesting only to calculate payload (which many ignore, albeit at their peril). The number of interest for regulators is Gross Vehicle Weight Rating (GVWR), as that's the manufacturer's specification of the heaviest the vehicle can be in as-sold configuration and still drive down the road safely.
Thanks for the clarification. The lowest GVWR among the f150s is about 6010 lbs which makes the IRS' apparently minimum weight make more sense.
> Curb weight is an irrelevant number, interesting only to calculate payload (which many ignore, albeit at their peril).
Not just their peril, also any road users or others nearby. If you've ever seen an overloaded pickup, they tend to drift around their lane as all the extra weight in the back reduces the steering authority on the front. Double so if it's pulling a badly loaded trailer that puts a lot of weight on the hitch
