Keep in mind that the cables lift the door. If the door is sitting on the ground and it is not level to the bearing plates then your door will not be level and may fall out of the tracks when raised. Here is a link to a web page that may help:http://www.truetex.com/garage.htm
So many people worry about the springs torsion but forget about the rest of the dangerous things associated with it. An unlevel door or a cable jumping off can lead to someone pinned under the door or the loss of a finger or two.