just a stupid question which I need an answer pls

Hi, dont laugh,

I just want to know, you guys know the mag on my car, the tyres for front and back are different sizes, 225 in front and 245 in back, does this mean the rim is also a different size, reason im asking is I was thinking of putting the one back rim in front, will swap tyres if possible

Let me know,

Its the normal sport rim to those who don't know my mag, on the e90

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Another stupid question, does both back wheels turn by the diff, or does the diff only turn one back wheel.