Never thought of it quite that way until a buddy of mine told me about a student replacing his factory steel wheels with lightweight Weld wheels. He said the kid could 'light them up' after the wheel change but couldn't before. Same tires, just lighter wheels.The same thing applies to the flywheel, and anything else that spins / rotates.
The 7075 T6 Aluminum flywheel with steel ring gear, 8 inch disc, floater plate and pressure plate in my racecar weighed 11.6 pounds total.Reducing rotating mass does indeed make a big difference!
I experienced this on my Yamaha 700 Grizzly Atv. I switched my Pitbull Growler tires from a traditional staggered set up of 26x9" fronts and 26x11 rears to my current 26x9 Growlers at all four corners . Well that shed 18 lbs of rotation mass of the rear axle. This made a HUGE difference in acceleration and overall fun factor on my quad!!! I can easily drift the rear end around up to 40 mph now.
Heavier wheel and tires will always need lower gearing to compensate... That's a Fact... Less rotation mass, means less need for more torque multiplicationWhen it comes to HP/torque loss, such articles are pretty useless as they never quantify the losses. Example: In computing up the HP loss for reducing a small block V8's internal rotating mass by around 5 lbs (easy to do with modern parts), the result varied between <1 and 2 HP. That's all it is ... out of 400-500 HP.
I've never worked up computation on wheel/tire masses to see what the effect is. Keep in mind that it is all related to gearing too..... the higher the gear, the less the acceleration rate of the cars and the wheels/tires, and so the less this particular effect becomes.
I agree with RallyBob, less rotational weight is better for accelerating and braking too. The powerband of your engine and drivetrain plays a big part. Racing with a stock geared transmission, build a high torque engine.Lighter wheels make a huge difference IMO.
Lighter engine parts...definitely, but you get more from large diameter things than small things. 5 lbs off a flywheel is far more noticeable than 5 lbs from a crank.
Similarly, lighter pistons and pins are more noticeable than lighter rods.
But I’ll take all lightweight parts over heavy parts any day. I suspect at sustained high rpms you’d want a heavier crank at least.