Since the AP2 front OEM RE050 have particularly narrow treadwidth 6.7" compared to other brands of that size. If I replace the front OEM size 215/45/17 with an identical size Kumho SPT (no tread width listed on tire rack or on Kumhousa.com), more than likely it will have a larger treadwidth than 6.7" of the front OEM RE050, can I go with Kumho SPT 255/40/17 in the rears since the fronts treadwidth will likely increase?

You may ask, well why not just go 225/45/17 and 255/40/17 on the SPT?
I have reservations of going to a Kumho SPT 225/45/17 fronts since the OEMs we're particulary narrow, and don't want a dramatic increase in treadwidth, in addition the weight increase is almost 2 lbs per tire!

I hope you understand my question. thanks