Bifold Doors

[John D v2.0]

You can have as much deflection as you like in the beam as long as the gap above the door is within manufacturers tolerances. In theory you could have a beam like a banana, or an arch, or going like a trampoline, and put a fillet in to make the top level enough, then as long as you use straps and no packers at the top, the door would be fine. However in reality your SE won't allow much deflection not least due to the masonry etc above.

 

[chappers]

absolutely and then additional to that most bifolds are then fitted with a slight upward camber so they stay put when opened.
there will be no std the mechanisms on each will have different tolerances before they start binding