The center dowel is completely, totally false security. If your cake starts gong sideways, the dowel will stay firmly implanted in the bottom board and tear right thru your cake. And as a final insult the cake will be so messed up you will not be able to fix it.
After discussing this with my DH, we decided that a single central dowel is really just a rod on which a cake can rotate 
, so...............
I now put in 2 full length stabilizing dowels. I use a diameter that seems reasonable for the size/weight of the cakes.
This weekend, I did a shopping bag cake that was 14 wide x 9 high x 4.5 deep--tall & thin. I used 2, 3/16" dowels thru the height, with 3 bubble tea straw supports in the bottom tier.
I make a template from parchment when I place my support dowels so that when I insert the stabilizing dowels there is no chance for me to hit the supports.
Nothing can rotate on 2 dowels. Yes, with extreme movement, cake can tear away from them, but with that kind of force, tearing cake is the least of my worries.
HTH
Rae
Quote by @%username% on %date%
%body%