I think they cut them and reseal the rubber with glue
You can even see the seam in the video
But that´s 4 tires to cut and glue! Easier to cut and glue the one post...
Well, when a post-daddy and a tire-mommy love each other very much, and the tire-mommy has a cuckquean fetish . . .
This is done by turning the tires inside-out and pushing them through horizontally. You need a machine to do it though because that rubber is very stiff.
why are people downvoting this amazing answer, lol
How does turning then inside out solve the problem of getting them on the post? I can't picture it in my head
Because the tire is topographically a radially flattened torus, when you turn it half inside out, it becomes a 2D möbius strip. At this point it effectively has only one side. When you push such construct horizontally against a solid, because the z-axis perpendicular to the strip has no negative values (it only has one side), if that coincides with the orientation of the ∇Np of the solid, the z vector wraps around the solid. When the tire snaps to its rest state (inside in), it's easy to see why it ends up around the pillar.
This 3D animation demonstrates the concept:
