A rope tow consists of a cable or rope running through a bullwheel (large horizontal pulley) at the bottom and one at the top, powered by an engine at one end. In the simplest case, a rope tow is where passengers grab hold of a rope and are pulled along while standing on their skis or snowboards and are pulled up a hill. The grade of this style of tow is limited by passenger grip strength and the fact that sheaves (pulleys that support the rope above the ground) cannot be used.