[torarne81]

Biggest reason that there may be used 6x2 vs 6x4 is that there is less tire wear on empty running. Here in Norway it's mostly trucks running volume transport that uses this combination.

Here we run with a maximum of 50 tons without dispensation, this can be done with combinations. 3 axles on the truck and a 3 axle trailer.

Maximum permitted total weight of truck with 3 axles is 26 tons regardless of whether it's a 6x2 or 6x4.

There are many different rules about this in Europe. For example, in the EU countries the maximum weight is 44 tons. And on top of this, there are special regulations in various countries.