I'm going with weight and diameter.
Diameter will alter the calculation for MPG. OP really hasn't said much about the new tires/wheels so I can't offer much in the way of how much error.
Thought I'd made a thread discussing tire diameter errors, but I can't find it.
Rotating weight is always in play, even at sustained speeds. It takes more power to keep it at speed.
121,000 members and still no sponsored racing.