A quad-bike vehicle (10) having a chassis (12), four wheels (14) rotatably mounted on the chassis (12), an engine (16) for driving at least two of the wheels (14), a seat (18) for a user, a handlebar (20) for steering at least two of the wheels (14), a tow-hitch (22), and a carrier device (24) for mounting on the tow-hitch (22). The carrier device (24) has a foldable platform (26), a back (28), and a tow-hitch attachment element (32) for releasable attachment to the tow-hitch (22). The platform (26) is foldable towards the back (28) to adopt a storage condition, and is foldable down to adopt an in use condition. Preferably, the platform (26) and the back (28) are both planar or substantially planar so that, when folded together, the platform (26) and the back (28) lie in parallel or substantially parallel with each other. With the platform folded down, the carrier device is spaced from the ground. A carrier device (24) which is specifically adapted for a quad-bike vehicle (10) is also provided.