id="p-0041" num="0042">Wheel carriage 200 has a forward end 202 and an aft end 204, and comprises a left sub-carriage 220L and a right sub-carriage 220R, with left sub-carriage 220L carrying a left forward axle 210LF and a left aft axle 210LA in tandem, and with right sub-carriage 220R carrying a right forward axle 210RF and a right aft axle 210RA in tandem. In the illustrated embodiment, each axle is shown carrying four trailer wheels 215. Trailer wheel sub-carriages 220L and 220R have respective left and right sub-carriage extensions 240L and 240R extending forward from forward end 202 of wheel carriage 200, with the forwardmost ends of sub-carriage extensions 240L and 240R defining respective sub-carriage extension tongues 242L and 242R, the purpose and function of which are described later herein.

Wheel carriage 200 is mountable to trailer structure 120 such that sub-carriage extensions 240L and 240R are laterally movable relative to each other and to trailer structure 120, such that wheel carriage 200 can be selectively transitioned between a laterally expanded configuration (as shown in FIG. 1A) in which sub-carriages 220L and 220R are displaced laterally-outboard relative to trailer 120, and a laterally-retracted configuration (as shown in FIG. 1B). This particular functionality is schematically illustrated in FIGS. 1A and 1B as being enabled by forward and aft telescoping struts 230F and 230A acting between sub-carriages 220L and 220R in conjunction with hydraulic or pneumatic cylinders (not shown). However, this is by way of non-limiting example only, as any functionally suitable and non-inventive means may be used for this purpose without departing from the scope of the present disclosure.

A distinguishing feature of embodiments in accordance with the present disclosure is that when wheel carriage 200 is in the expanded configuration and trailer 120 is carrying little or no load (as shown in FIG. 2A), wheels 215 on forward axles 210LF and 2102RF will be clear of the road surface RS while wheels 215 on aft axles 210LA and 210RA bear on road surface RS (as is typical for unloaded cambered trailers), but when wheel carriage 200 is in the retracted configuration (as shown in FIG. 2B), wheels 215 on forward axles 210LF and 210RF will be close to or in contact with road surface RS. As may be understood with reference to FIGS. 1A, 1B, and 3A-6B, this functionality is enabled by providing:

- a first transverse component in the form of a first cross-beam 130 incorporated into trailer structure 120 at a selected distance forward of aft end 114 of trailer 110, and defining laterally-elongate left and right “tongue slots” 132L and 132R configured to respectively receive sub-carriage tongues 242L and 242R; and
- a second transverse component in the form of a cross-beam 140 incorporated into trailer structure 120 aft of the first transverse component, and defining laterally-elongate left and right “fulcrum slots” 142L and 142R configured to respectively receive an intermediate region 244L of left sub-carriage extension 240L and an intermediate region 244R of right sub-carriage extension 240R;
  
  wherein:
- tongue slots 132L and 132R in first cross-beam 130 respectively define left and right upward-facing guide surfaces 134L and 134R for respective engagement by downward-facing contact surfaces 243L and 243R (which may be flat or contoured) on sub-carriage extension tongues 242L and 242R, with guide surfaces 134L and 134R respectively comprising:
  - outboard (upper) sections 135L and 135R;
  - inboard (lower) sections 137L and 137R at a selected distance lower than outboard sections 135L and 135R; and
  - ramped sections 136L and 136R extending between and contiguous with, respectively, outboard and inboard sections 135L and 137L and outboard and inboard sections 135R and 137R; and
- fulcrum slots 142L and 142R in second cross-beam 140 respectively define left and right upward-facing horizontal guide surfaces 144L and 144R for respective engagement by downward-facing contact surfaces 245L and 245R (which may be flat or contoured) on intermediate regions 244L and 244R of sub-carriage extension 240L and 240R.

Accordingly, when wheel carriage 200 is being transitioned from its retracted configuration (as shown in FIGS. 1B, 2B, 3B, 4B, 5B, and 6B) to its expanded configuration (as shown in FIGS. 1A, 2A, 3A, 4A, 5A, and 6A), by moving sub-carriage extensions 240L and 240R outward relative to trailer 110, contact surfaces 243L and 243R on sub-carriage extension tongues 242L and 242R will respectively move:

- outward and out of contact with inboard (lower) sections 137L and 137R of guide surfaces 134L and 134R of tongue slots 132L and 132R in first cross-beam 130;
- outward and upward along ramped sections 136L and 136R; and
- further outward and into contact with outboard (upper) sections 135L and 135R of guide surfaces 134L and 134R;
  
  while contact surfaces 245L and 245R on intermediate regions 244L and 244R of sub-carriage extension 240L and 240R respectively move horizontally outward along guide surfaces 144L and 144R of fulcrum slots 142L and 142R in second cross-beam 140.

Similarly, when wheel carriage 200 is being transitioned from its expanded configuration to its retracted configuration, by moving sub-carriage extensions 240L and 240R inward relative to trailer 110, contact surfaces 243L and 243R on sub-carriage extension tongues 242L and 242R will respectively move:

- inward and out of contact with outboard (upper) sections 135L and 135R of guide surfaces 134L and 134R of tongue slots 132L and 132R in first cross-beam 130;
- inward and downward along ramped sections