Are you going to rant about this every month?
http://www.xoutpost.com/bmw-sav-foru...s-bmw-etc.html
Once again, if it were me, I would go this route;
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If you want a full size spare tire that bad, just go out and buy an additional wheel and tire. There is plenty of room in the back of the X for that.
With regard to what you are supposed to do with the flat tire, just throw it in the back of the X. You can't possibly be talking up 100% of the cargo area in the X when you drive around normally. If you do, the X probably isn't the best choice for you in the first place as it does not even have that great of a cargo capacity. Let's say you do actually carry a ton of stuff everywhere you go, how would you get to the spare tire if you needed it? That is right, you would have to pull everything out of the cargo area to get to it, then reorganize and repack everything. Then you would probably be complining about why the tire isn't mounted under the vehicle.
There are plenty of solutions to this problem and I have to say that it is a pretty silly reason to not buy another BMW. Do you drive over nails and shards of glass for fun or something? Do you get a lot of flat tires?