Tires: 1992 Bronco 4w tire size, differential problems, rotating tires

Question
The tires on my Bronco are slightly larger than what came on the car. My front tires are nearly new, but I need to replace my rear tires.
I would like to move my front tires to the rear and the rear wheels to the front using the correct tires size. It isn't much of a difference but the larger tire size had cut my turning radius down.
The tire company says this isn't recommended by Ford as the different size tires (front to back) would cause differential problems down the road.
My manual says that when rotating tires, should the front tire be different from the rear then rotate side to side. This seems to be contradictory.
Thanks for the advice.
RD Welts

Answer
Richard,

I've noticed that vehicle manuals don't seem to cover 4X4's very well - and you've stumbled on it, too!

Clearly, when a 4X4 is in 4WD mode, the diameters of the front and rear tires need to be the same.  Otherwise, the drivetrain will bind up.  Something has got to give.  While it might be the tires that slip, it could also be some component in the drivetrain - and when those break - well, let's just say it's very expensive.

So your tire dealer is warning you in the only way he knows how.  

To take this a step further, in order to insure that the drivetrain does not break, the front and rear tires have to be identical - same size, make, model, and state of wear.