On Sat, 08 Dec 2012 01:38:45 -0600, Vic Smith wrote:

Only thing I disagree with is one spring vs two.
Too many advantages make 2-spring well worth the extra little cost.

I corrected that assessment in a subsequent detailed response to
rightfully recyclebinned who also disagreed as you did.

The advantages of two torsion springs are (summarized):
1. When one spring breaks, the door goes down softer.
2. When one spring breaks, the door goes up softer too!
3. Balanced spring forces are gentler on the cable drum flags.
4. With each spring doing half the work, you have greater spring choices.
5. Winding two springs is only half the work per spring.

The disadvantages weren't listed, but some of them a
1. Two springs generally costs (slightly) more than one spring.
2. Two springs are generally (slightly) longer overall than one spring.
3. Two springs are generally (slightly) heavier than one spring.
4. Two springs are (slightly) more effort to install than one spring.
5. Converting from one spring to two spring has to be done correctly.

Let me know if I missed any pros and cons.