What axle drives on tandem truck?

Answer 1

Tandem refers to the number of axles at the rear of the vehicle... there are a couple different configurations which can be used with this setup. The first is the 6x4 setup - six wheels (counting dual treads as one wheel), and four of them having power supplied to them for driving the vehicle.
This is also known as a twin screw setup, and is typically seen on North American tandem trucks... the driveshaft goes from the transmission output into a power divider.. the power divider is essentially a differential which supplies power to both of the drive axles continuously... many get under the impression that the power divider lock actually engages the second drive axle, but this is not true - the lock causes outputs to each drive axle to rotate at matching speed - in normal operation, it's unlocked, and allows the outputs to rotate at non-matching speeds... this is important to preserve tires, as you might have more worn tires on one axle than the other.
The other configuration is 6x2 or 4x2 (+2), the latter being common in Europe, where the additional axle is a tag or pusher which doesn't allow for additional weight, but is intended to decrease damage to roadways by distributing the weight over more area... in either case, this is known as single screw, and the dead axle often can be lifted.... or, there are systems which simply adjust pressure in the suspension air bags to put maximum traction on the live axle... this was intended primarily for the N. American market, as this system removes 400 lbs. of weight from the vehicle... however, the Canadians are stalling this from catching on, as they declared the dead axle a lift axle (which it isn't), and restricted the amount of weight which could be carried on it.

Answer 2

typicall both rear axles drive, some may only use the first rear axle but typically both rear axles are driven axles