Quote:
Originally Posted by nikitopo
Math do not lie, but you have to model the problem correctly. You asked twice about total weights and diameters. A total weight and diameter is enough ONLY for the solid pulley. On the OEM pulley you have two different pulleys the one inside the other joined together with a rubber. You need the diameters of both and the weights of both. No one can really provide these numbers, unless someone takes apart the pulleys and measures the two weights. Then you have to create a model that the inside pulley is rotated by the center hub and the outside pulley is rotated by the inside pulley. With such model you would find that the rotation inertia is MUCH BIGGER and it not only relevant to the weight difference. As said before it is a complex problem and there are unkonwns in the equation (i.e. the weights of the OEM pulleys). It is much easier to make some measurements and see how the car behaves with standard tools like the virtual dyno app.
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Are you trying to imply that the inside and outside parts of the crank pulley rotate at different rates? The angular velocity and acceleration of all three pieces (inside metal, outside metal, and rubber gasket) are the same. They can be treated as a single item for this purpose.
I'll tell you what, I'll even pretend the pulleys are thin-walled cylinders of the outside diameter to give you the maximum possible inertia improvement. I still feel modelling the pulleys as solid disks is the best approximation for a comparison, seeing as aftermarket can't actually change much about the inside hub or outside surface without compromising function, but whatever.