Whats the deal with fly wheels anyway

[10clock]

i thought the whole i dea of a flywheel was momentum
so why do they offer a "lighter" flywheel

I WANT good answers on this one

[ASUFocusSVT]

I think about it like this, with a lighter flywheel you allow the motor to spin up faster, by allowing less drag on it. If you can allow the motor to spin up faster you are in the heart of the power faster. Also, think of it like this could you personally run faster dragging something that is 25 pounds or something that is 12 pounds?

[dwtalso]

Energy storage in the flywheel is for drivability. On a road car a heavy flywheel stores some momentum, holding the motor at speed when the clutch is released, and making for an overall smoother ride. A light flywheel in such a car allows the motor to drop speed very fast. This causes surging and bucking during shifting. Also, a heavier flywheel smooths out the motor's idle.

On a high performance car weight is evil. The light weight fly wheel makes less drag on the motor, saves overall vehicle weight, and allows for faster rpm changes. The latter means that turbos spool quicker and it's easier to manipulate the throttle setting during heal-and-toe shifting.

For a car that spends a great deal of time WOT the drivability stuff doesn't matter. For mild performance cars most drivers accept the compromise and adjust for the idle and shift conditions required during normal commuter driving.

[Euro_SVT]

Lighter revs faster, but stalls easier on the low end...

Flame suit on:
I also have a 4 banger Jeep - some guys add an "inertia ring" a weight to the flywheel. Revs slower, but ya won't stall it in the rocks!
(Yes, I have a red neck)
Flame suit off:

It's all about momentum - the lighter flywheel is easier to get moving but it's also easier to stop/slow down... the heavier takes more energy to get moving, but it's harder to stop/slow.