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      10-08-2012, 08:33 AM   #217
jerseygirl
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Drives: 2010 e92 m3
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Quote:
Originally Posted by swamp2 View Post
Still disagree. Getting way OT but...

Consider two equal masses m, a distance d apart, say equal to a wheelbase. This is an idealized two point mass "car". This results in 50:50 weight distribution and the polar moment I(about cg) = m d^2/2. Alter the weight distribution radically so 100% is on one axle. Weight distribution = 100:0, total weight unchanged. Now here I(about cg) = 0. For the more general case you can solve for the generalized I about the cg for any value of m1 and m2.

I = (m1 m2 d^2)/(m1+m2)

Again even though m1+m2 is fixed change their ratio and you can compute exactly how I changes.

Through this simple example you should be able to see that axle weight distribution and polar moment are intricately linked. You can extrapolate to the case of a continuous variation in mass along the length rather than two point masses. In both cases though change one and you change the other. In the simple cases there will be an analytical solution, in the general case certainly not.

Good book by the way!
thanks for clarifying that. now its so simple