A method of operating a tufting machine to form tufted articles, comprising: - moving a backing material through the tufting machine; - feeding a series of yarns (Y1, Y2) to the needles arranged along at least one needle bar (11, 11') for forming a series of tufts in the backing material; - characterised by: - reciprocating the at least one needle bar (11, 11') carrying a series of spaced needles therealong toward and away from the backing material with a plurality of drive assemblies, each drive assembly comprising a series of drive gears, a pair of cam arms (65, 66), each cam arm (65, 66) connected to one of the drive gears of the series of drive gears so as to be moved in a substantially linear reciprocating motion by the rotation of the drive gears, a rocker arm extending between and moving with cam arms (65, 66), and a push rod pivotally mounted along an intermediate portion of the rocker arm and connected to the at least one needle bar (11, 11') for imparting the substantially linear reciprocating motion of the cam arms (65, 66) thereto; - varying a rate at which selected ones of the series of drive gears are rotated, said varying the rate comprising operating drive motors coupled to a first drive gear of the drive gears at different rates; and - in response to varying the rate of rotation the selected ones of the drive gears, reorienting the rocker arms of the drive assemblies with respect to the pusher rods mounted thereto so as to adjust a stroke of the at least one needle bar (11, 11'). - moving a backing material through the tufting machine; - feeding a series of yarns (Y1, Y2) to the needles arranged along at least one needle bar (11, 11') for forming a series of tufts in the backing material; - characterised by: - reciprocating the at least one needle bar (11, 11') carrying a series of spaced needles therealong toward and away from the backing material with a plurality of drive assemblies, each drive assembly comprising a series of drive gears, a pair of cam arms (65, 66), each cam arm (65, 66) connected to one of the drive gears of the series of drive gears so as to be moved in a substantially linear reciprocating motion by the rotation of the drive gears, a rocker arm extending between and moving with cam arms (65, 66), and a push rod pivotally mounted along an intermediate portion of the rocker arm and connected to the at least one needle bar (11, 11') for imparting the substantially linear reciprocating motion of the cam arms (65, 66) thereto; - varying a rate at which selected ones of the series of drive gears are rotated, said varying the rate comprising operating drive motors coupled to a first drive gear of the drive gears at different rates; and - in response to varying the rate of rotation the selected ones of the drive gears, reorienting the rocker arms of the drive assemblies with respect to the pusher rods mounted thereto so as to adjust a stroke of the at least one needle bar (11, 11'). - reciprocating the at least one needle bar (11, 11') carrying a series of spaced needles therealong toward and away from the backing material with a plurality of drive assemblies, each drive assembly comprising a series of drive gears, a pair of cam arms (65, 66), each cam arm (65, 66) connected to one of the drive gears of the series of drive gears so as to be moved in a substantially linear reciprocating motion by the rotation of the drive gears, a rocker arm extending between and moving with cam arms (65, 66), and a push rod pivotally mounted along an intermediate portion of the rocker arm and connected to the at least one needle bar (11, 11') for imparting the substantially linear reciprocating motion of the cam arms (65, 66) thereto; - varying a rate at which selected ones of the series of drive gears are rotated, said varying the rate comprising operating drive motors coupled to a first drive gear of the drive gears at different rates; and - in response to varying the rate of rotation the selected ones of the drive gears, reorienting the rocker arms of the drive assemblies with respect to the pusher rods mounted thereto so as to adjust a stroke of the at least one needle bar (11, 11').