First of all, the motor will make the same amount of torque, regardless of the weight of the flywheel, the gearing or the weight of the vehicle. Torque is merely the amount of rotational force the motor can generate. Period.

The Flywheel Stone: A Fable by Neo

For this example, let's take a massive 500 lb. granite grindstone. That's going to be our flywheel. Now, let's say it's hooked up to a large crank with a long handle. There's 10 guys standing there turning that handle and spinning the grindstone. (From this point on, the grindstone will be known as the "flywheel stone") On the other side, we're going to take another 200 lb. disc, the same diameter as the grindstone, and it will later press against the face of the grindstone. This other disc is going to represent the clutch and we will put a load on it, say, a large arm that goes into a vat of molassas. So there's going to be a lot of resistance to keep this clutch disc from rotating. Ok, we have the situation set up, right?

Because the flywheel stone is 500 lbs., once it's in motion, it's gonna want to stay in motion. That's the law of inertia and momentum. When that clutch disc is pressed against the flywheel stone, it's going to 1) slow down the speed at which the flywheel stone is spinning by putting a load on it, and 2) accelerate to the speed at which the flywheel stone is spinning because of the momentum of the weight of the flywheel stone. The ten guys spinning the flywheel stone won't have to work as hard to keep it in motion and the molassas begins to get mixed.

However, now we have a new problem. The arm going into the vat of molassas is moving slowly, and instead of mixing it, it's only gently stirring it. So now, we need the 10 guys to speed up the stirring arm by increasing the speed of the flywheel stone. Easier said than done. Whereas the momentum of the heavy flywheel stone worked to their benefit when the clutch disc was dumped on it, it's now working against them when they're trying to accelerate the flywheel stone. It's just so darn heavy that it takes them much more effort to get it to accelerate.

A lighter flywheel stone would have been harder to keep in motion when the clutch disc was "dumped" on it, however, they could have compensated for that simply by spinning the flywheel stone a littler faster before dumping the clutch disc on it. There still would have been a drop in velocity, but it would have made accelerating the mixing arm a lot easier after the initial "clutch dump" because less weight would have resulted in less load, which would have translated to less rotational resistance.

So, after this long winded story on how weight affects the rotational speed of the flywheel stone and it's ability to turn the clutch stone and mixing arm, what have we learned?

We have learned that, in both processes, we had the same 10 guys, making the same amount of power and torque, to rotate the damn flywheel stone.

The power output never changed. Now, the important thing is to find a balance. Where the flywheel has enough weight to carry enough momentum on the launch (Which can be accomodated for by spinning it at a higher rpm to begin with.), and where it's light enough so that it takes less effort to increase the speed of it's rotation...