ORIGINAL: Lees07GT

It is also important to consider overall tire/wheel height. If your new combo has a taller height than what you started with, you will have reduced the engine rpm at a given speed. This has thesame effect as reducing your rear end gear ratio. Anytime you go to a larger wheel, you should go with an appropriate lower profile tire to maintain your overall gear aspectif, in fact, you want the effective gearing to remain unchanged.

ORIGINAL: CrazyAl

1. Speedo error: Only the outside diameter of the tire affects your "gearing" and speedo error. Rim size (16, 17, 18, 19, 20, etc.) has nothing to do with this.

2. Larger rims are worse for acceleration even if the total package is the same weight as what you had before. Inertia is derived from the product of mass and radius. Larger wheels carry most of their weight at a larger radiust. For example, suppose your stock 17" wheel and tire package weighs in at 50 lbs. You switch to 20s, and suppose those also weigh 50 lbs. (which means very light 20s). The 20's have higher inertia than the 17s because even though the weight is the same, the 20" set carries that mass further out from the center of the wheel. In order for a 20" wheel & tire package to have a the same inertia as a smaller-wheel-diameter package, the 20" combo would have to be lighter, which is extremely unlikely.

3. Technically drilled brake rotors are lighter, so switching to them would save some weight. However it is a TINY bit of weight. I'd be suprised if it was more than 2 or 3 ounces per disc. The only truly effective way to save weight is to buy race-oriented wheels which are actually designed for light weight, not looks like most wheels are.