It's not strictly mass, it's moment of rotational inertia of the rim+tire combo, that matters during speed change. Mass at the center hurts you less than mass at the rim. There is a correlation, but a poor correlation between total mass and rotational inertia. I wish rim makers would publish an inertia figure, but they don't.
At constant-ish highway speed, rim aerodynamics is a much bigger factor. The more closed the rims are, especially at the outer edge, the better. The edge is where the airspeed of the forward rotating part of the rim is 2x your ground speed, and could have 4x the drag of the rim passing through 3 and 9 o'clock positions...
At constant-ish highway speed, rim aerodynamics is a much bigger factor. The more closed the rims are, especially at the outer edge, the better. The edge is where the airspeed of the forward rotating part of the rim is 2x your ground speed, and could have 4x the drag of the rim passing through 3 and 9 o'clock positions...
