[MVF4Rrider]

Originally Posted by Dodge2Dub

It does make sense and I understand the example of adding a passenger vs. being a lonely driver...but...if you change the mass of an object (wheel) that you want to rotate (we'll say decrease it) against a surface, then it becomes easier to rotate it (less force). So, doesn't it stand to reason that if less force is needed to rotate that object ,the translation of applying the same input power is that the object (wheel) will spin faster (increased acceleration)? If so, then if we draw a line on the ground, the power measured when the vehicle crosses over that line with the heavier rotating object (wheel) will be less than the power measured when the vehicle crosses over that line with the lighter object (wheel). Essentially, you are at a higher RPM when you cross the line with the lighter wheel (screw the object reference) then you were with the heavier wheel.

You're not adding/increasing power, you're freeing up some normally lost power (perhaps too little to notice in most cases). Keep in mind also where the wheel weight is located makes a difference to rotating mass efficiency. The outer most area is most important in terms of mass/lightness than the center. Switching too an overall lighter wheel helps (as it's probably well engineered and lighter in the rim area over stock). So does switching to a lighter tire. Tires can vary considerably in weight. PS2s are very light. Some alternatives can be several pounds heavier each. Something to consider when replacing tires. But anything toward reduced unsprung wight has many benefits (acceleration, braking, cornering). Ceramic brake discs only weigh 1/4 the weight of OEM. That's a huge reduction. Too expensive to add on but reasonable as an option extra for cars so equipped. Lighter wheels are hard to feel in a road car. On a motorcycle, carbon or magnesium (or forged aluminum) make a gigantic difference vs cast aluminum in terms of performance. Extremely noticeable.

As for reducing weight of engine parts such flywheels and clutches, there you would feel an appreciable difference in how fast the motor builds power. The downside is the power is not stored as easily due to less rotating mass and the power can be somewhat of a light switch, making it harder to apply power in bends. On a Ducati I once had, I replaced a 4 lb. flywheel with a 8 oz one. Power delivery was incredible, and so was the engine braking! Off throttle was like applying the brake. It was also difficult to keep the front wheel on the ground. I had also replaced the clutch with a considerably lighter one. So the rotating mass was incredibly affected.