Hi Frank,
I agree with all the comments you've received so far, but cant emphasise enough the importance of the offset. I have gone through a wheel changing exercise myself on my Audi and it took me months and months to find wheels I liked and that would fit. The offset can determine where on the hub the wheel will sit and whether its likely to fowl any brake or suspension components. Fortunately there are easily accessible websites that can give you a guide indication of how your new wheel will fit, they will ask you for your existing wheel fitment and the new wheel fitment your proposing. They will ask you for the existing and new wheel radius and width, and also existing and new tyre sizes. They will also ask you for the offset of both existing and new wheels. The offset is often referred to as the 'ET' followed by 2 numbers and this is usually stamped in the wheels casting on the back of the rim. Just as an example my existing wheels had an offset of ET31 (stamped on the reverse of the rim) and the new wheels I was proposing had an offset of ET40. If you want a smooth and not so bumpy ride, try and and avoid tyres with a profile of less that 40.
Hope this is helpful