I did a quick and dirty 4x4x4 in order to test some things and the test was good, but portal hubs was not. We all know Ackerman steering, pivot points and such terminology when it comes to steering techniques. I think - but I would love to be proven wrong - that the geometry is all wrong. no way a vehicle would have this kind of geometry that the portal hubs give you, right? the LEGO Part 11949 - Technic, Steering Portal with 2 Pin Holes and 2 Ball Joint Arms from the 42000 is a good way to go. But from what I heard it could be a bit wobbly on a heavier machine? Anyway, here are some pics on my trial!