If I have stock 18inch wheels should I have an 18inch space saver?

looking to source one for the levorg and the one on fb is 17inch. The seller says its correct but I'd rather be safe than sorry.

I do plan to go to 19inch once @prodrive come back to me.

 

pretty sure the Levorg uses similiar 315mm front brakes to the Legacy SpecB and so shouldn't be an issue

 

I wasnt sure if a 17 would effect the 4x4 system

 

its the overall diameter including the tyre NOT simply the rim size.........