There was a lot of speculation on TFW2005 that the hot rod car mode actually goes nose-first into the trailer and the back wheels of the hot rod car are what form the cab wheels of the truck.

The truck cab mode is completely different to the car mode and some of the unpainted prototype pics show that the windshield section and hood of the truck cab are actually attached to the bottom of the trailer and would likely be pulled down over the rear section of the hot rod car.

That theory seems to hold up pretty well looking at the painted pics.

Its an ingenious if a little unconventional transformation.

I am in love with the toy. True engineering genius!!!!

It would be an added bit of coolness if the Rodimus Prime robot mode is slightly taller than Hot rod. It certainly looks that way in the pic but I can't see if the limbs elongate or not.