Dont know about Ifor/trailers but sometimes its the weight legals that limits how many you can put in - our small horsebox would fit in about 50 but to be stable and legal its only about 38. . Im sure someone will give a max bale figure (depends on size of bales a bit too)ure but do then also calculate weight versus your trailers load capacity.
i can get 30 in my Rice Beaufort
Which doesnt help you much,,,
But!
to start off filling the trailer - Bales on 'Sides' making an A shape to fill the front of the trailer - then 2 bales - on 'ends' to fill in the 'A' gap.
When my boy was off work for a few months and we weren't using the trailer (ifor 505) we stored our hay in it, i think we managed to get around 20 bales in it but could have got more in if we needed! We never towed it with the hay in it though! Hope that helps
Internal dimensions of a 506 are apparently 3.16m x 1.67m x 2.26m which is 124" x 65" x 89" or 717340 cubic inches.
An average bale will be 14" x 18" x36" or 9072 cubic inches. Weight 20kgs?
So dividing one by t'other you could, in theory, get 79 bales in a 505 (assuming it is the same size as a 506 and no allowing for the curved roof). Weight about 1.5 tonnes.
we got 33 small straw bales (could have got a couple more and slammed the top doors on them) in our 505 the other weekend. Def wouldn't have got 40 in though even with expert packing.