Something else to consider is the weight reduction, and also the reduction of rotational inertia. Generally, the rim will have more of an effect on rotational inertia than the tire.
Inertia resists movement, so rotational inertia will resist rotation. Less R.I. will mean it's easier to accelerate, so you are reducing the load on the engine. Therefore, you can accelerate to the same speed with less effort: more efficiency!
- The further away mass is from the center of rotation, the more inertia.
- The more mass, the more inertia.
Unless you are rockin custom Carbon Fiber rims, your rim is going to be the main factor for inertia. Using the aforementioned principles, best thing you can do is get a smaller, lighter rim. Then, going a step further, you can get a smaller tire. This will lower your car, pushing more air over the top, reducing drag created from the turbulence on the underside of the car (unless you have installed an effective underbody.) AND, you'll be reducing the overall weight of the car. It's a win-win-win!
