44 air passage 43 connects tire 41 and bore 46 provided in axle 44 to the bore 46 there is connected a pivoting air connector 45 through which pressurized air is supplied to inflate tire 41 at will the axle is supported by bearings 47 which are connected to swinging arms 48 as can be seen in fig1 and 14 these arms 48 are fulcrumed by pin 50 which enables them to swing up and down pin 50 is supported by the base structure 51 which is rigidly connected to the base of the floor frame 38 a spring 52 is mounted intermediate swinging arm 48 and support 51 when tire 41 is inflated via conduit 37 contact will be established between the tire 41 and pallet 3 fig1 when air valve 36 is open air from tire 41 will escape thus the tire will be pulled downwardly by spring 52 and disconnected from pallet 3 the said spring would also resist the force created by motor 54 and belt 55 on axle 44 as seen in fig1 the propelling system is in contact with pallet 3 when tire 41 is inflated when motor 54 is activated its rotation is transferred by belt 55 to wheel 42 and by tire 41 to pallet 3 the engagement of tire 41 and pallet 3 is disconnected when the air is released through valve 37 and the spring pulls the wheel downwardly pressurized air being supplied via conduit 37.