TBD was design for a much smaller monitor resolution and before responsive design took over the modern web.
Here are our desktop stats for the forums:
Screen Shot 2016-04-23 at 1.56.09 PM.png 92.1KB 2 downloads
and for mobile:
Screen Shot 2016-04-23 at 2.00.22 PM.png 87.57KB 1 downloads
I'm thinking max width should 1200 to 1366.