Has anyone ever put 225/45 on their 17" wheels? I'm currently running 215/45 but would like to add a little sidewall. I want to make sure 225/45 will fit.

 

It is possible to put 225/45-17 tires on stock MINI 17x7 wheels and use a MINI with stock suspension.

However the 225/45-17 tire is too tall at 25" to be a good fit for clearance.
Stock tire diameter is 24.4" and would be a better choice although you can use tires that are slightly less in tire diameter.

If you want to use tires with more sidewall then-

215/45-17 gives you a little more than stock 205/45-17.