It is not being anal about 2 axle or 3 axle, it is the correct description of the truck on the REG. along different braking dynamics, you go to BUY a 3 axle truck, but only has 2 axles, do not think "oh no big deal, I dropped 1 axle, but things are ok because the reg. states it is a 3 axle" is going to go far. 2 or 3 axle has a lot to do with the allowed GVWR, some states look at 2 or 3 axle as the amount of ware an tare on there road ways (3 axle more ware then a 2 axle) so the truck is taxed accordingly. When they ask for the unladen weight, and how much you want to load, they are going on the assumption that the load weight legal window is inside of the GVWR (axles, length, ect) and that you know what is legal, the weigh station and DOT may have a different idea.
The number of axles and length are a major IMPORTANT component of the GVWR,
Yes, I agree with you that the number of axles and length are major factors in a vehicle's GVWR. But as I mentioned before GVWR means little to
most states when it comes to registration/tags. They know a heavy truck is going to create more wear and tear on the roads and that's why the registration fee is based on the total weight you want to haul and not the vehicle's unladen weight (except Alaska), number of axles, or amount of tires touching the road. That's why they have weighted tags in the first place. The key words in my statement though are "most states". Are there a few states that are more picky and want to know how many axles a vehicle has? I wouldn't doubt it, but they are few and far between and not the norm. The rest of the states don't care how many axles you have as you can have a 26,000 pound rated truck with three axles or a two axle truck rated at 38,000 pounds. The DMV people mainly care that you pay for the amount of road damage you might do based on that weight. But yes, a few states might want to know the amount of axles a vehicle has but as I said that is not the norm and I did specify "most states". I know a few states may be different so I know better than to say "all states".
Anyhow, it's mainly the DOT people that might stop me for a random inspection that are going to care what the data plate says in regards to GVWR and that my loaded weight does not exceed it or my registered weight. They are the ones that would ticket me for excess weight if I put the suspension and axles from a 10 ton truck under a five ton and exceed the 5 ton's GVWR that's on the data plate as that's where the GVWR means the most. But as long as the registered weight is not exceeded DMV in most states doesn't care. It's mainly the DOT people that are going to come after you.
But as I said you are correct that the number of axles has a major effect on a vehicle's GVWR. If you convert a truck from a tandem setup to a single rear axle then the GVWR on the data plate is no longer valid. That I'm not challenging. Yes, you should get the truck inspected to have a new weight rating assigned to it due to the change to CYA but if you're driving an empty bobbed deuce and a half or 5 ton then the GVWR on the data plate means nothing as you aren't any where near that number, though you may get in trouble if you are driving a bobbed 5 ton without a CDL due to the data plate indicating you might need one. Now if you get stopped with the bobbed truck at or near it's original GVWR then expect all heck to break loose as you will most likely receive a nice pile of tickets due to that GVWR being invalid.
As far as my comment about CA being anal that was in regards to how they have a requirement for anyone driving a tandem axle truck to have a CDL, even a WWII 1.5 ton Dodge 6x6 even though it's GVWR is well under 26,001 pounds, just because it has tandem axles. The Feds, along with most of the U.S., only require a CDL if the GVWR exceeds 26,000 pounds. They don't care if it has 2, 3, or 4 axles. It's the GVWR that matters to most states, not axles. So for CA to say all drivers of tandem axle trucks must have a CDL even if the GVWR is under 26,001 pounds is just anal to me as even the Feds don't have this requirement. I have no problem if they want to list the number of axles on the registration. It's the CDL required based solely on having 3 axles and not based on GVWR that I was talking about as they are the only state I know of to do this.
The main reason I was bringing up converting a 6x6 with tandem rears to a 4x4 was in regards to your comment about how doing so means the vehicle is no longer an antique truck. That I've never heard of and that's what my question was about as I have never seen a state issue a new build date for a vehicle just because a person replace a set of tandem axles with a single. That's all I was trying to clarify as your comment didn't make sense to me.
Changes to the vehicle's status on the registration as far as 2 or 3 axles (if that state lists that on the registration but as I said most don't) is a separate issue and not related to the vehicle's antique status. Changing a 6x6 to a 4x4 does not mean the vehicle is no longer an antique and not eligible for antique plates as the year it was built didn't change. That's all I was trying to point out. My apologies to the OP if I'm to blame for taking this thread off on to a tangent.