garf, going with a larger diameter rim will have no/minimal effect on the braking of the car provided you stick with roughly the same diameter tire (ie, the two tires are the same height). So, for example, you can go from say 225/45R17's to 225/35R19's and be just fine. If you go with a wider tire (ie, the first number of the tire size), you may run into a rubbing issue depending on how much wider you go. I have an X-type, so, just how wide you can go, I am not sure.

You can go with a larger diameter tire too, but again, you may run into a rubbing issue. On my truck, I went from a 30" tall tire to a 37" tall tire without changing anything in the brake system. yes, the truck takes longer to stop. But, as long as you know it is going to do that, you can plan accordingly. While this is an extreme condition relatively speaking with your car, it goes to show that modern day braking systems can handle a much larger tire. Now, I will admit, I do go through pads a bit faster now because I do end up stepping on the brakes a bit harder.

Keep in mind that normally going with a larger diameter rim while keeping the overall tire diameter the same will result in a net increase in the tire/rim weight. This means you have more rotating mass, which will lead to slightly less mileage and slightly increased braking distances. But, I don't think you will be able to really notice this.

 

You probably have your own plans, but I think going from 17's to 19's is the biggest 'jump' I would make, and it will make a positive difference in the appearance of the vehicle. I would also keep the overall diameter and width as close to the original as possible, maybe just one size wider perhaps...no need to test the fender wells too much.

When I got my larger tires on the stock wheels on my Jeep (little wider, 2 sizes taller), the tire installer obliged my request to install them on the front real quickly so I could check the clearance in the wheelwell in a full turn of the steering wheel. I liked being able to do that.

good luck