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Old 09-11-2009, 04:33 PM   #41 (permalink)
orange4boy
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Sorry to be a killjoy but...

I've read some physics threads on the subject of rotating mass and those factors you guys are quoting are really high. They calculated more like between 1.5:1 to 4:1 but so much depends on how far from the axis the weight is. ie. One lb of tire weight has more effect than 1lb of rim weight etc. It also depends how fast you are accelerating. If you are drag racing then it makes a big difference.

Physics thread:

Rotating Mass when keeping a minimum weight Text - Physics Forums Library

Tuner thread:

Reducing Rotating Mass: Ditching Dead Weight [Archive] - Bimmerforums - The Ultimate BMW Forum

Quote:
I ran similar numbers for the M3 flywheel just to see how they'd come out. I'm calculating a 1% acceleration difference in 1st gear going from a 26lb fly to a 12 lb fly, ignoring all other rotational mass (gearbox, wheels, driveshaft, accessories, etc). In this case that's like dropping 31.5lbs off the car's weight, or 2.24lbs for each pound of rotational mass drop. This doesn't seem like the dramatic difference that people seem to feel.

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