Hhhmm I've been thinking about all this - Giovanni I reckon you are on the right track. It is all about reducing inertia.
And Willy-RS4 I think what you heard about the reduced torque is also right. But in a good sense. Follow my argument. Hey I'm no exepert I'm just thinking out loud and trying to put my school phyisics to use.
If an object that is free to rotate about an axis it is difficult to set into rotation, its moment of inertia about that axis is large.
Inertia = Mass x Radius^2. (squared) Therefore, you can have two different flywheels, rims etc that weigh exactly the same but their mass is distributed at different radi resulting in significantly different values of inertia.
Torque = Inertia x Angular acceleration (i.e. rotational acceleration)…. (2)
Therefore, from equation 2 above, any reduction in inertia (e.g. reducing the weight of a flywheel or rim of the same radius) would result in a reduction in torque.
But this is a GOOD reduction in torque!
This is a reduction in the torque required to accelerate the inertia. In other words, the engine has to exert less torque to the flywheel, rims etc in order to produce the same angular (rotational) acceleration.
Therefore, leaving more torque to accelerate everything else like the gearbox, drive shafts, wheel bearings, basically anything that is being put into motion.
But before you all go mad buying the lightest flywheels or have your stock ones machined etc.
a flywheel by definition is designed to have a high value of inertia. An engine needs a method of storing its rotational energy. A four stroke engine only produces a power stroke every forth cycle. So something has to keep the crankshaft spinning to keeping the piston stroking, the camshaft rotating to push the valves open against their springs, the water, oil, power steering, AC pumps rotating etc etc until the next power stoke 3 cycles later in a 4 stroke engine. The inertia of the flywheel is the specific device for maintaining this rotation.
So hence at low RPM there is a potential for the engine to stall if you reduce the mass of the flywheel too much.
I've heard of examples of lightened flywheels where the engine runs ok until high load is put on the engine at idle. For example, by the alternator caused by switching on the rear heated window, turning on the lights, operating an electric window in combination with the AC unit while turning (power steering). Resulting in the engine stalling unless higher than idle rpm is maintained – Clearly too much inertia, usually in the form of mass has been removed.
So given the above I would have thought the single most effective and practical uncompromising mods to reduce inertia and increase acceleration times would be to fit lightened allow wheels and a lightened flywheel.
