Dolly Trailers
Dollys for road trains
A dolly is an auxiliary axle equipped with a fifth wheel that allows coupling a conventional semi-trailer as a trailer via drawbar. It is the key component in megatrailer (25.25 m) and ecocombi road train configurations, combining rigid truck + dolly + semi-trailer.
Common configurations
- Rigid truck + dolly + semi-trailer: Up to 25.25 m and 60 tonnes (in authorised countries).
- Tractor + semi-trailer + dolly + semi-trailer: Double trailer. B-Double configuration common in Australia and Nordic countries.
Single-axle versus twin-axle dolly and fifth wheel
A single-axle dolly is lighter and cheaper, suitable for moderately loaded semi-trailers in light EMS configurations. The twin-axle distributes the load better and allows a higher combination GVW, essential to approach the 60 t of Nordic mega-trains. Check the fifth-wheel condition (play, slide plate, king-pin lock), the drawbar, the eye coupling and the BPW/SAF axles. Coatrucks states the number of axles, fifth-wheel type and towing capacity on every dolly listing.
Dolly homologation and registration in Spain
The dolly is registered as a standalone trailer and needs its own type approval and MOT. To run in megatrailer (25.25 m) or ecocombi configuration in Spain you need special DGT authorisation and approved routes, since the ordinary limit is 18.75 m. For intra-EU import it's worth confirming the dolly has a COC or documentation that allows its homologation. Coatrucks handles the import and Spanish registration of the dolly and advises on the requirements of the road-train configuration you want to build.
Used dollys
Dollys for ecocombi and road trains.
Frequently asked questions
How much does a used dolly cost?
Price depends on the number of axles, fifth-wheel condition, suspension (air or leaf spring) and brand. Coatrucks publishes ex-VAT prices with real photos of the fifth wheel, drawbar and axles.What is a dolly and what is it for?
A dolly is an auxiliary axle fitted with a fifth wheel that lets you couple a conventional semi-trailer as a trailer, via a drawbar and eye coupling. It's the key part of megatrailer (25.25 m) and ecocombi road-train configurations, combining rigid truck + dolly + semi-trailer, or tractor + semi-trailer + dolly + semi-trailer (B-Double). Coatrucks advises on the optimal configuration for your operation.Single-axle or twin-axle dolly: which to choose?
The single-axle is lighter and cheaper, suitable for moderately loaded semi-trailers in light EMS configurations. The twin-axle distributes the load better on the ground and allows a higher combination GVW, essential to approach the 60 t of Nordic mega-trains. The choice depends on the weight you'll tow and the country's regulations. Coatrucks states the number of axles and towing capacity on each listing.How do I inspect the fifth wheel of a used dolly?
Check the fifth-wheel play, the slide plate condition, the king-pin locking mechanism and the jaw wear. Also check the drawbar, eye coupling, BPW/SAF axles and suspension. A worn or loose fifth wheel is dangerous and costly to replace (€800-2,000). Coatrucks verifies the lock operation and the fifth-wheel condition before delivering each dolly.Do I need a special permit to run a dolly in Spain?
Yes, for megatrailer (25.25 m) or ecocombi configurations in Spain you need special DGT authorisation and approved routes, since the ordinary road-train limit is 18.75 m. The dolly must be registered as a standalone trailer with its own MOT. Coatrucks handles the dolly's registration and advises on the legal requirements of the road-train configuration you want to build.How often does a dolly need an MOT?
In Spain a dolly is registered as a standalone trailer and undergoes an annual MOT from the first year. It inspects the axle(s), brakes, suspension, lights, tyres, drawbar, eye coupling and especially the fifth wheel and its locking mechanism. A fifth wheel with excessive play is grounds for rejection. Coatrucks delivers each dolly with a valid MOT and the fifth wheel inspected.Is there warranty and financing on used dollys?
Sale between professionals, with no warranty: the vehicle is sold as it stands, and you can come to Lleida to see and test it before buying. Coatrucks performs a full pre-delivery inspection of the fifth wheel, drawbar and running gear. Financing through BBVA Autorenting, Santander Consumer and BNP Paribas Leasing, with 24-60 month terms and a 10-30% deposit. We also handle intra-EU import and Spanish registration.What other names does this type of vehicle go by?
It is also known as dolly, converter dolly. They all refer to the same vehicle — you'll find them all here.