The highway department does it by using scales which are just large enough to accommodate one set of wheels.
What type of truck and trailer? For all I know, you could be talking about a Ford F650 and a single axle utility trailer. If you're referring to Class 8 vehicles, something like a single axle tractor towing a single axle trailer would be allowed an interstate GVW of 52,000 lbs.
Depends on what type of truck it is. It could be a single axle truck, a tandem axle truck, a tractor-trailer. You'd have to narrow your question down a bit. Tare (empty) weights will be affected by make and model of the vehicle, frame length, construction of the body, etc.
Five
Your tractor drive tandems could weigh in at 34,000 lbs, but you could only have 20,000 lbs. on the single axle of the trailer.
A ten foot spread axle trailer is allowed 20,000 lbs. per axle, for a total of 40,000 lbs.
25,000 - 40,000 lbs. or more, depending on specifics. When you say "tractor-trailer", you're citing an all-inclusive category which would include everything from a single axle tractor pulling a 28' single axle trailer up to heavy haul units of over 20 axles... I've personally run combinations which have weighed in excess of 250,000 lbs. empty.
Yes
You need to be more specific about the configuration. Is a single axle straight truck, a tandem axle straight truck, a tandem axle straight truck with additional lift axles, a tractor trailer...?
An 18 wheeler consists of a tractor (meaning something that pulls) and a trailer (meaning something that follows.) A semi tractor-trailer rig has a trailer that sits on top of the frame of the tractor on a coupling device called a "fifth wheel." The tractor has ten wheels with two on the front axle and four on each drive axle in the rear. The trailer has two axles with 4 wheels each. The tractor and trailer together are informally called a rig. Is that what you were after?
what kind of lorry? a 7.5 tonner will weigh around 4-5 tons empty, a four wheel rigid 18 tonner will weigh around 8-9 tons empty. add an extra ton for each additional axle. a solo tractor unit will be around 7-8 tons, coupled to a tri-axle curtainsider the weight empty will be around 15 tons, coupled to a fridge trailer closer to 18 tons empty. subject to design weights/taxation class, a 4 wheel tractor coupled to a tandem trailer can be loaded up to 33 tons, a triaxle trailer up to 40 tons, a six wheel unit coupled to a triaxle trailer can go up to 44 tons
A tandem truck usually refers to the amount of axles on the trailer or tractor. A single drive axle on a tractor would be referred to as a single, or the same for one axle on the trailer. I have seen it referred to the amount of tires on the end of an axle. When there are two tires on the end of the axle, that would be referred to as a dual, not a tandem.
Some companies put the tare weights on the side of their vehicles. Otherwise, could get a scale ticket, from which you'd deduct the weight of the fuel and payload. Or you'd have to contact the manufacturer's of the tractor and trailer (or a dealership may be able to provide you with this information). Typically, for a standard five axle unit, tare weight will be between 30,000 - 36,000 lbs. (approx 13,600 - 16,330 kg.).