As others have said, you got 4 things to consider:
1.
The nameplate rating by the manufacturer.
This is basic! If the person that built it says it can only carry a certain amount of weight and you exceed that, you are overloaded.
Now, there are many trucks that are underrated so car drivers can run them, and if you want you can sometimes get the manufacturer (or another vehicle completer) to re-rate it for you based on the actual mechanical capacity (in which case they also make a new nameplate for the truck), but then they are opening themselves up for liability so don't count on it.
2.
Fed/State DOT max axle weight/max group weight/Bridge Formula
For the truck you are talking about, you don't need to worry about this as much because you are so light. In CA they will let you across the scales with 20K on a single axle and 34K per set of doubles, but that doesn't mean that if the CHP inspector checks he won't look at axle ratings and bridge formulas.
3.
Tire Sidewall rating.
This rating is predicated on having the correct tire pressure for max weight.
I ran a tiltbed pintle hitch trailer that is rated at 52,600 lbs GVWR and the spec sheet says it can handle a 42,000 lb load, so the boss assumed that they could slap a 38,000 paver on there no problem.
I started working there and the first time I loaded the paver on I knew it was overweight just from looking at the tires.
Took it to the nearby quarry scales and found that it was putting 42,000 pounds on the trailer axles.
The max DOT allowable for the set is 34k, and the combined sidewall rating was only about 40K, so there's 2 tickets right there! (and a safety issue)
I tried loading the paver further forward but the rears on the 10-wheeler went over 34k before the trailer got under 34k, and then the steer tires hardly had any weight, and then I was exceeding the Bridge Formula because the wheelbase wasn't long enough to have both sets a 34K.
My point was you have to make sure your tires are rated for the load carried, despite what any tag might say!
4.
Mechanical capacity of the vehicle.
If you have a truck rated at 25,500 with hydraulic brakes, I wouldn't care what the axle weight ratings are or what the tires are rated for, I would be worried about the brake ratings!
Most of the other things mentioned are mainly paper violations and might be able to be easily reasoned away in your mind (although not so easily in court!), but if you are overloading the design capacity of the truck or any components of it, you are endangering your life. Never mind, I don't care about your life, but I do care about the life of my family and everybody else on the road!
Note I didn't mention registered weight in there. That's because in many states (such as CA) that is a declared number. I can register a truck at the unladen weight, and if I have a fat driver in it with full tanks get an over weight ticket.
(I had something like that happen a few years ago at United Rentals when they changed to the declared weight system. They registered an F550 flatbed at the unladen weight, and I got pulled into the scales and written up as overweight with just a generator in the bed. Had to wait for them to fax the Owner Responsibility paper over... Don't leave home without it I learned that day!)
I see large trucks with very low stickers because all they haul is insulation or corrugated drain pipe.
So, basically you have to look at the GVWR, the individual axle ratings, the tire sidewall ratings (and air pressure), and the registered weight, and make sure you don't exceed any of those. If you are towing a trailer, then you got to also think about the Bridge Formula, hitch rating, GCWR rating on the truck, over 10K=license class jump, etc.
In the Mack 10 wheeler I am driving right now (~24K empty), I can get 12 tons in without overloading anything if it is stacked all the way in the front of the bed. If the pile reaches the tailgate my drivers will be overweight (DOT 34K), and if I go over 12 tons the front axle will be over it's rated weight (14K). I even have flotation tires on the front rated at 10K+, but the nameplate on the axle is only 14K, so...
You basically got to try different loads and check each axle weight separately to find what is legal and safe.
Ya, it sucks not being able to get a "Full Load", but it's a lot safer, and your truck will last a lot longer too! (not even counting the damage from the tree and minivan full of kids that gets taken out when the brakes go out)
Ben~
