Hi Sid, I am not an engineer, but I do believe that drivers of performance cars, should not move too far away from essential parts of the design of their car as it left the factory. The specification for the x type AWD, which I checked up on when I had one, was 16" and 17" wheels, although I was reliable informed that 18" wheels would fit perfectly well. I am also reliably informed that you get a more comfortable ride on 16" wheels rather than 18" wheels. My S type 2.7D, which is a much heavier car that the x type AWD petrol, has 18" wheels which is the mid point between the wheels specified by Jaguar of 17" 18" and 19" wheels. With that in mind, I think that 17" wheels are ideal for the AWD x type. My Rover Sterling 2.5 litre automatic was a slightly lighter car than the x type ran on 15" wheels and fave a very comfortable ride over the 11 years I had it. But it was not a performance car, and rather good for passengers. I would be inclined to keep the 16" wheels on through the winter and see how they perform on the road on a car that holds the road extremely well. Trying something out is often a bit better than investing in something that might not work as well. Regards, Peter.