Greetings fellow Corrado addicts, I have a set of Audi Parobols on my C and am running a set of 205/40/17s on them. I am due to replace them and wanted to replace them with 225/45/17s which is the tyre that originally came on that rim- I dont like the stretched look of the 205s and they are so low profile wise, its like riding on solid rubber- no air!!!!! HAs anyone got any experience here- I was advised that this jump of 50mm in tyre diameter from the original 205/50/15's would cause all sorts of problems mechanically...Let I know.....Thanks and remember- "The EarlyByrd catches the car in front"
The profile of a tyre (height) is calculated according to it's width (so for ex. a 205/40 would be different from an 225/40). And a lot depends on the width (ET) of the rim ("friendlier" ET for Corrado is close to et35). Since you don't have coilovers (or lowering suspension) my opinion is that 225/45 would not look that good (from the aesthetics point fo view, the tyres would look like baloons ). Most people running 17''s (and et close to 35) and don't like "stretch" choose 205/40 (or 215/40 max). I used to run 205/40 on 17''s (had coilovers and 5mm spacers though)...it looked good but was a bit harsh on bad roads. Don't also forget that 225/45 MAY rub inside the arches if you don't have pulled/rolled arches and you decide to lower the car in the future. My best bet for compromasing both looks and handling would be 215/40 but the best thing to do to decide is drive a car with similar tyre/rim spec of yours and see which one you like best
See username Piky from Slovenia for exactly the same spec as you describe (Audi TT 17''s on 225/45 with original suspension
Hope someone else from here with more experience can help you on this issue Cheers!
I'm replying a bit late, but 225/45/17 on parabols is a no-go!
The tyres rub on the inside!
You can see the pic in my profile, I just putted them on, to see how it looks.
Still waiting to buy 205/40/17 tyres for them... LoL
You can simply use a tyre calc, to see how it would roughly look:
Byrd
Tornado
). Most people running 17''s (and et close to 35) and don't like "stretch" choose 205/40 (or 215/40 max). I used to run 205/40 on 17''s (had coilovers and 5mm spacers though)...it looked good but was a bit harsh on bad roads. Don't also forget that 225/45 MAY rub inside the arches if you don't have pulled/rolled arches and you decide to lower the car in the future. My best bet for compromasing both looks and handling would be 215/40 but the best thing to do to decide is drive a car with similar tyre/rim spec of yours and see which one you like best 
Piky