My 56 plate Blobeye WRX is ready for her first set of new tyres.

Its currently got 215-45-17 Potenza's
What I want to know is can I stretch 225-45-17 on to the same rim?

Will it affect the handling?
Will it look odd?

Sorry if its a stupid question but I havent got a clue about tyres.

 

Not a stupidd question. Firstly go here and type in your tyre sizes.
You will find you are within the recommended limits as regards speedo readouts. As for the tyre size it depends on the rim width, your handbook should tell you how wide the rim is, i do not know on those.
Changing tyres sizes - tyre size change calculator

 

The WRX runs 7J wheels (ie 7" wide) where as the STI has 7.5J running 225's.

Therefore the tyre may look a little wide for the rim, a 7J is min size for a 225 iirc.

Also, as shown by the tyre calc that Madass directed you to , the sidewall will be higher (45% of 225 is more the 45% of 215 IYSWIM..?), however this is still within tolerance etc..

One things for sure, a newage looks under tyred on a 215..!

Go the whole hog and fit some nice lightweight 18's (7.5 - 8J) with a 225/40..

<<<<<<<<<<<<<<<<< as here..