Re: Wheel and trye experiance?
your owners manual should list all the tyre sizes availabe from Alfa just stick to these to be safe and comply with insurance.
if this is not available you may need to base the rolling radius on the stock smallest wheel as there may be a difference from your current set up already. i know that it does not quite work on the gtv as the base wheel is a 15" steel wheel for the european 1.8 i guess.
the 215/45/17 and 225/45/17 don't provide the same rolling radius although this should not cause a problem. if you go for a 225 try a 40 profile as this should be a closer match [although i know alfa supply a 225/45 as standard on some models]
rule of thumb is if you go up in wheel diamter 1" you go down one profile size ie 50-45 or 45-40. this is modified if you increase the tyre width significantly as well.
if the rolling radius is bigger than the original it just means that the speedo will read a 'truer' speed. most speedos read 5-10% low so just be aware of this regard speed traps etc
If ignorance is bliss, why arenít more people happy?