[Twix]

I have the stock 421 sport line wheels. No idea what the specs on them are besides they're 18x8J. I believe the offset is 34. I use the original wheels for the winter.

The wheels you're looking at won't work. The fronts, they would stick out 8mm further. They would most likely rub and you'd need to roll your fenders. The rears, see if you can get et 27-29.

The most you would want to do on the front would be 8.5 30et. Anything else might rub at full lock or rub the fender on compression. Especially if you're lowered.

Outer diameter matters, for two reasons. They must match. Otherwise you'll destroy your xDrive unit. If you go too big or too small, you'll run into your speedo not reading correct and your odo will lie. I think my tires are about .3" bigger than stock.

I don't really know what you're asking about in regards to if I replaced my original setup or not. I went from stock BMW wheels to aftermarket.

If you can, see if you can get that front to be somewhere around et 26-28. See if the manufacturer makes it, they probably do. Also, make sure the centre bore is for E9X BMWs or you'll have to use hub centric rings.

So try to see if this works for the wheels you want:

Front: 19x8.5J et 27
Rear: 19x9.5J et 28

That would be about the same extremeness as my setup. No fender rolling or trimming the rear liners.

Look up willtheyfit. com, that place you can mess around with dimensions to see what will give you a good fit. Keep in mind, going with a smaller number et than what I have and you may experience rubbing. Anything larger would be ok, but you lose the flush to the fender look.