What is the maximum speed a tractor towing a trailer must not exceed outside built-up areas?

Special vehicles and combinations of vehicles, also special ones, even if only one of those making up the combination is of such a nature — if they lack brake signalling, if they tow a trailer, or if they are motor cultivators — the maximum speed at which they are permitted to travel is 25 kilometres per hour.
If they can reach 60 km/h on a flat road, their maximum will be 70 km/h, and the rest of the special vehicles will have a maximum of 40 km/h.