Off @-@ site , the new brake wheel and fantail were made . The original brake wheel was too rotten to repair , and showed evidence that it had been altered from the original one installed in 1819 . The original brake wheel was 6 feet ( 1 @.@ 83 m ) diameter to allow the Common sails to run at their optimum speed . When the mill was modernised in 1832 it was necessary to alter the gear ratios within the mill , as Patent sails run at a slower speed than Common sails . The great spur wheel was increased in diameter and the stone nuts reduced in diameter . The brake wheel was also rebuilt , with a cast iron segment ring fitted in place of the original cogs , resulting in a wheel 7 feet 2 inches ( 2 @.@ 18 m ) in diameter . The opinion of professional millwrights was sought , and it was decided that a scaled @-@ up version of the original brake wheel would be made , but retaining the cast iron teeth segments . The remains of the original brake wheel were retained as an exhibit in the mill . The original iron segments were all broken , so a pattern was made and new segments were cast in heat @-@ treated malleable cast iron . When the brake wheel was completed it was dismantled and transported to the mill ready for reassembly .