If you look into
http://www.dunloptire.com and search for 245/50/15, they measured rim width is actually 7", while the approved range is 7" to 8.5".
225/50/15 all around is a good size for drifting, I think with a wider contact patch in the rear you get sharper handling and more traction.
In that case, maybe 225/50/15 front & 245/50/15 rear is more ideal.The only tire that has these sizes is SP8000, what do you think of this tire?