The rear differential is geared so that the rear half of the propeller shaft turns 8% faster than the front half to ensure that no drive goes to the rear wheels in normal road driving when the only the front wheels drive and the rear ones get dragged and rotate the rear propshaft/VC just slightly faster. The VC is not activated by this small speed difference, for if it was, it would try to slow the rear wheels, which wud be a braking effect on the car.
Technical References:
Landrover Workshop Manual (Description and Operation) 47.6, states:
“The rear wheels are 0.8% under driven, so in most conditions the vehicle is effectively front wheel drive, with the rear wheels turning the rear propeller shaft slightly faster than the IRD drives the front propeller shaft. Since the speed differential is low, the increase in viscosity of the silicon jelly is marginal and there is little resistance to relative rotation of the slotted discs."
However, the rolling diameter of worn tyres on the rear compared to new one on the front could adjust the 0.8%, hence the advice to fit new tyres to the rear in preference to the front. Wrong tyre pressures and conflicting rolling diameters can create a braking effect in the VC and have an impact on fuel consumption.
One on front and one on rear would seem to be theoretically the best solution for VC issues but there may be a conflict with braking balance across axles although I imagine that ABS would counter such a problem?
This is a shame, because since the front tyres do more braking than the rears, it would normally be a preference to have the best tyres where they are needed more.