06 Shelby

Need some advice on this one. We have an 06 V6 mustang with factory 16 inch wheels, we are thinking about installing 17" x 9" wheels on it. We where told that if we went with a 17"x9" wheel we would have to install the steering stop 4R3Z-3932-BA. And if we went with an 18" wheel we would have to install the steering stop 6R3Z-3932-CA.

Could anyone out there tell us if this is correct steering stops to use or do we really need them.

Thanks