Five
A typical tandem axle tractor has 6 brake chambers.
Tandem by definition is two. So tandem axle is two axles. Example would be a tractor trailer having two axles next to each other is a tandem axle.
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.
That depends on what the configuration is.. is it a single axle, tandem, tri-axle, quad, centipede, etc.?
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...?
In idle? The configuration of the tractor has nothing to do with determining that. It's the motor which does, and the consumption rate in idle for a motor would be the same for a tandem axle dump truck as it would be for the same motor in a road tractor, box truck, quad axle dump truck, cement mixer, etc.
I've always heard 10 HP for every 1 ft of implement
The most common North American 6x4 tractor and tandem trailer combinations have a total of five axles, as do the most common European/Asian/North African configurations of 4x2 tractor and tridem trailer.
It depends on the commercial vehicle, how it's licensed, the state it's running in, and a lot of other things, but a tractor-trailer combination with tandem axles on the tractor and the trailer can generally carry 80,000 pounds--12,000 on the front axle and 34,000 on the tractor and trailer tandems.
Depends on the truck and configuration (e.g, tandem axle dump, tractor-trailer end dump, etc.).
They come in many sizes and configurations. They could be single axle trucks, tandem axle trucks, tandem axle truck with additional lift axles, tandem axle trucks with a twin steer setup (and these may also have additional lift axles, as well), and even tractor-trailers with mixer trailers. You'd have to be a little more specific as to which one you had in mind.