Is offset the the distance between the outboard rim flange and the mounting surface?

Yes, offset refers to the distance between the outboard rim flange and the mounting surface of a wheel. It can be measured in positive, negative, or zero terms, depending on the position of the mounting surface relative to the centerline of the wheel. Positive offset means the mounting surface is closer to the front of the wheel, while negative offset indicates it is closer to the back. This measurement affects the wheel's alignment and overall vehicle handling.