Tractor unit explained: difference from a truck, 4x2 to 6x4 axle configurations, fifth wheel coupling, cabs, engines, manufacturers and a used-buy checklist.
The tractor unit is the engine of European long-haul transport: it has no load space of its own, but a fifth wheel coupling on which a semi-trailer with a 13.6 m load length rests. Together they form the articulated truck (Sattelzug) with a permissible gross combination weight of 40 t. Which axle configurations, cabs and engines exist, what fifth wheel load and kingpin mean, which manufacturers and models dominate the market, and what matters when buying and selling used tractor units.
A tractor unit (also called a truck tractor, or Sattelschlepper in German) is a commercial vehicle with no loading platform of its own that carries a fifth wheel coupling behind the cab. The semi-trailer rests on this coupling via its kingpin; part of its weight – the fifth wheel load, 10 to 12 t depending on the vehicle – is thus carried by the tractor unit, the rest by the semi-trailer's own axles. Together the two form the articulated truck.
The difference from a rigid truck in the narrower sense: a rigid truck has a fixed body – box, flatbed, tipper – and, where applicable, pulls a trailer as a drawbar combination – for example with swap bodies in general cargo transport. The tractor unit has no body and cannot move any load without a semi-trailer. Its advantage lies in the separation: the semi-trailer can stay at the customer's site for loading and unloading while the tractor unit pulls the next one.
Cab: long-haul cabs with a flat floor, two bunks, storage space, parking air conditioning and a parking heater (Mercedes-Benz GigaSpace and BigSpace, MAN GX and GM, Volvo Globetrotter XL, Scania Highline and Topline, DAF Super Space Cab) as opposed to low regional-haul and construction cabs. The cab is a major price factor when buying used, because it determines suitability for long-haul use.
Engine: inline six-cylinder engines with 10.5 to 16 l displacement and 360 to 680 hp; 420 to 510 hp is the common output in long-haul transport, 600 hp and above in heavy haulage. Transmission: automated 12- to 16-speed gearboxes (Mercedes PowerShift, Volvo I-Shift, Scania Opticruise, ZF TraXon) are standard; manual shifting is now found almost only in older construction vehicles. Auxiliary brake: retarder or intarder – in demand for Alpine and heavy-haulage transport and a significant value driver.
Emissions standard: Euro 6 has been mandatory for new registrations since 2014 and today shapes the used market; the Euro 6c, 6d and 6e stages differ in their limit values. For German tolls, the CO₂ class is also relevant. For export, the emissions standard is often decisive, because many destination countries require minimum standards – the guide Exporting used trucks lists the rules by country.
The fifth wheel coupling (usually Jost or Georg Fischer) receives the semi-trailer's kingpin, which is a uniform 2 inches across Europe – so any tractor unit fits under any semi-trailer. Sliding fifth wheel couplings allow the axle load distribution to be adapted to the semi-trailer. The permissible fifth wheel load is stated in the Zulassungsbescheinigung Teil I (vehicle registration certificate part I) and, together with the axle loads, limits how heavily the vehicle may be loaded. Further interfaces: compressed-air couplings (red and yellow), ABS/EBS connectors, lighting connectors to ISO 7638, and increasingly telematics.
Seven manufacturers share the European market: Mercedes-Benz (Actros, Arocs for construction), MAN (TGX, TGS), Volvo (FH, FH16, FM), Scania (R, S, G, P), DAF (XF, XG, XG+, the new XD), Iveco (S-Way, Stralis) and Renault Trucks (T, T High, C, K). Added to that is Ford Trucks (F-MAX) with a growing share in southern and eastern Europe. The most liquid segment of the used market is the Actros, TGX, FH, R-series and XF in 4x2 with Euro 6, automatic transmission and long-haul cab – they sell fastest across Europe and in export.
Tractor units lose value faster than semi-trailers or low-loaders, because the engine, emissions standard and mileage age, and fleets replace them wholesale after three to five years. But that is exactly what makes the market liquid: three- to six-year-old 4x2 Euro 6 tractor units find the most buyers across Europe. Value is determined by make and model series, year of manufacture and emissions standard, mileage, transmission and retarder, cab size, axle configuration, tyres and maintenance history; from around eight years old, export takes over price formation. A concrete figure for your vehicle is provided by the free valuation based on real sales; verified dealers from 35+ countries then submit binding offers – sell your tractor unit with truckoo.
A rigid truck has its own body and can load itself. The tractor unit has no loading platform, but a fifth wheel coupling on which a semi-trailer rests; only the two together form the articulated truck.
The first number states all wheels, the second the driven ones. 4x2 means two axles with one driven, 6x2 three axles with one driven plus a trailing or leading axle, 6x4 three axles with two driven.
In Germany, 40 t permissible gross combination weight, 44 t in combined transport and for zero-emission vehicles. The payload is 24 to 27 t depending on unladen weight.
Class CE. In commercial freight transport, the professional driver qualification with code 95 is also required.
Mercedes-Benz Actros, MAN TGX, Volvo FH, Scania R and DAF XF in 4x2 with Euro 6, automatic transmission, retarder and long-haul cab – they have the highest demand in Europe and in export.
Gabriel Böhm is Managing Director of truckoo GmbH, the digital platform that is redefining commercial vehicle trade in Europe. With a passion for innovation and efficiency, he shapes the strategic direction and drives operational excellence to connect sellers and buyers smarter, faster and more transparently.
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