The Big J4T was designed at a time when articulated tractor units and trailers were becoming commonplace. The 2-axle tractor was available as a 24-26 or 30-32 G.C.W. vehicle, and with wheelbases of 108 inches, 114 inches, and 145 inches.
The 32 ton model became the most popular 32 ton tractor unit in the United Kingdom. It could be fitted with a dual 46 gallon petrol tank to give a capacity of 92 gallons, and so was ideal for long distance use.
Like the other models in the 'Big J' range, the 'Big J4T' was built on an all-bolted frame assembly for added strength and rigidity, and had a spacious and comfortable cab, with a wide windscreen and good all-round visibility.