By better, I assume you mean more efficient. The smaller the width of the contact patch (tire), the more efficient.
http://en.wikipedia.org/wiki/Rolling_friction
http://en.wikipedia.org/wiki/Low-rol...sistance_tires
http://www.treehugger.com/files/2005...olling_res.php
When I had 175 MM contact patches at each corner, I had better average fuel economy than my current 185 MM width tires. (I do a lot of highway driving)
My technical knowledge regarding about diameter not impressive, but big tires take more energy to get moving. Smaller tires take less. Think of those little go kart tires. Easy to get them moving, but you are more limited in speed and are more dependent upon changing gears.
Forged rims are very lightweight, but cost a lot of money. If you are lucky, maybe you can find some small, discontinued set for $100 per rim. Usually the aerodynamic profile of these rims are the complete opposite of aero hubcap covers. These rims will be much stronger than steel rims. Good brands that i know of are BBS & SSR.
http://www.tirerack.com/wheels/Wheel...All&sort=Brand
http://www.tirerack.com/wheels/Wheel...All&sort=Brand
Use google for more. (not entirely sure those links will work)
Hope that helped
