There are two kinds of spring systems. Extension springs are simpler to install. They function in pairs, stretching along either side of the door, parallel to the ceiling. They need about 10 in. of headroom.
Torsion springs go over the opening of the door.
They work by winding and unwinding in place when the door is raised or lowered. The torsion spring distributes the weight of a door more evenly than do extension springs, making them better suited for extra-heavy or wide doors. They require 12 in. While the former is perfectly serviceable, the latter gives a more finished appearance to the mechanism and can cut down on the noise of the door for just a few dollars more. On higher-quality steel rollers the ball bearings are housed in sealed races.