I just finished building The Globe (set #21332), and I'm curious what the purpose of the four rubber tires on the interior of the model is (highlighted with red box):
I had hoped that towards the end of the construction process their purpose would somehow be revealed, but sadly that didn't happen.
My best guess is that they are some sort of counterweight to prevent the globe from always settling into a certain orientation, but due to the tilted axle and the overall weight of the rotating part there seems to be enough friction to prevent the globe from moving by itself. Also, the tires, though somewhat heavier than regular Lego parts, don't seem to be adding a significant amount of weight.
My second guess was that the tires are some kind of assembly aid that would help with handling the (admittedly somewhat unwieldy) globe in a later construction step. However, I did not encounter any point in the assembly process where those tires would have been helpful in some way.
Does anyone know what the actual purpose of these elements is?