Quote:
Originally Posted by swamp2
Fair enough. I will respectfully disagree back, but this time with a wealth of evidence to make my case.
Have a look at the table below. I have made a nice spreadsheet (and even attached it for the real nerds) to calculate wheel moment of inertia (among other things). As you can see in your particular cases colums D vs. E and F vs. G the larger wheel (despite not being quite apples to apples in terms of widths) uniformly have MUCH larger moments of inertia. The moments are larger because of the effect of the wheel, not the tire. The larger wheels have a much higher concentration of mass at a large distance away from the center of rotation. I can't quite follow/decipher your "reasoning" above but it is not correct and does not arrive at realistic numbers, trends nor conclusions. Your insight here is simply flawed.
Once again (for the E9X M3)....
18s for performance
20s for looks
19s for a decent compromise
And of course the driver will be an even bigger factor than these differences.

What if you are going to 20's and the wheels are actually 34 lbs. per/wheel lighter than the stock 19s. How does that factor into your inertia equation?