Ford Falcon: Tyres for XR6

You could fit the 235/45/17 tyres, but to be legal they would have to have an "Extra Load" rating to match the load rating of the 245/45/17 tyres, and that might make them more expensive. If you did make the change and used "Extra Load" rated tyres you would have to run a slightly higher inflation pressure to bring them up to the load carrying capacity of the 245/45/17 tyres. In the view of our tyre specialist, Russell Stuckey, making such a change as you are   contemplating would be a backward one.