Alfa, can you clarify what you mean by the lower offset please? What lower offset are you referring to? Since he was planning on using the stock rims doesn't the offset stay the same? I thought, perhaps mistakenly, that the offset was a function of the rim design and dimensions and not the tire.
The all rims/wheels (whatever you call them) may have different offsets.
The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types (measured in millimeters).*
Zero Offset
The hub mounting surface is even with the centerline of the wheel.
Positive
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
The hub mounting surface is toward the back or brake side of the wheel's centerline. "Deep dish" wheels are typically a negative offset.
If the offset of the wheel is not correct for the car, the handling can be adversely affected. Often, when changing the width of the wheel, the offset will also need to change to maintain proper clearances inside the wheel well. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly. We test fit thousands of different vehicle and wheel size combinations to confirm which ones work correctly. Our extensive database allows our sales staff to offer you the perfect fit for your vehicle.
*Backspacing, similar to offset, is the distance from the hub mounting surface to the inside lip of the wheel (measured in inches).
Good luck.