Originally posted by rodneyk
From what I've heard, people use the largest rim necessary solely for the purpose of clearing brakes. Even when you go to a larger rim of the same weight, the increased rolling diameter still requires more torque to spin compared to a smaller rim.
I'm no expert in this, so i'll let someone explain the details 
i think up until 18" it doesnt really matter. i mean if you have a 15" wheel and tire, and a 17" wheel and tire, and both wheel tire wheighs the exact sameit wouldn't make an difference, because the rim is taller, but the tire is shorter, making them still the same size together.
sorry for all the commas and if this doesnt make sense.