standard size is 17x7.5 +30 offset for the 2011-on SR5, so when you going lower, the centre of the wheel is gonna sit towards the outside of the car more. For eg.
Zero Offset - 0 Offset
The hub mounting surface is even with the centerline of the wheel.
Positive - + Offset
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
Negative - - Offset
The hub mounting surface is toward the back or brake side of the wheels centerline.
Depends if you want the wheels flush with the guards or not, or have an aggressive look with the wheels outside the guards (which will attract the boys in blue a lot more).
Hope this helps, correct me if im wrong!
Vehicle #1: 2013 SR5 - plenty of mods to come.... hopefully
Vehicle #2: 2009 CBR1000 - maxxed out.. lol