wheel sizes

of course you can, just make sure the stud pattern on the new rims matches the car, and get lower profile tires to avoid rubbing. keep in mind that after you change your wheel size, your speedometer will actually say that your going slower than you really are. (ex it says your going 55 but your actually going 58) so watch out and don't get speeding tickets.

if you go up 2 inches in tire size then go down 2 inches on tire thickness. your speedo wont change at all then. it might be a good idea to upgrade the brakes though depending on how good they are.

the best way to know if they'll fit and what sizes to get is go to tirerack.com when searching for tires use the upgrade a size icon and it will display the other optional sizes u can fit

Sure, you can put almost anything you want on it. Remember when choosing tires to pick one that is close to stock diameter if you want the speedo to be correct. Most any tire shop will be able to suggest alternate sizes and there are pleanty of websites that have a tire calculator.

Yes you can, but just because the wheels fit does not mean they are right. you need to check the back space (or off set) is with in tolerance. You also need to make sure that the centre of the wheel fits over the hub corectlly for example if it is to loose you will suffer from vibration or from wheels coming loose, if it is to tight it will bind up and give the same problems if they are loose you can get a thing called a PCD ring that will take up the slack, you need to remember the weight of the car sits on the wheel not the wheel studs. Generally if you go up one size in wheel you need to go wider one size to keep the rolling diameter the same but speak to your local tyre store for the correct fitment.

the offset is a very important part to look at. if its to far off, then you will wear out your wheel bearings much faster. also most cars can accommodate a wheel tire combo that is about 2 inches larger in outer diameter without rubbing. the thing to watch if your not going up much (17 is max no higher on your car) is wheel width.Example: if your car is a 5inch wide wheel go no larger than 7 wide with proper offset. a smart thing to do would be to find a forum that specializes in your car. (for Subaru people IWSTI.com is where we go) these places can give more specific info on your car. all most of us here can do is give general info that will get you in the neighborhood