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Sept. 11, 2014, 5:23 a.m. -  craigsj

#!markdown Going through Keith's data: First, he didn't use identical wheel builds but biased the data in favor of 650B. Using identical wheel builds to 3 digits, the wheel weights should be 3830, 3990, and 4130 grams. This ignores that fact that the tubes could be the same. The relative weights are -4% and +3.5%, already different. Next, Keith botched the effective rotational radius numbers completely. He used rim diameter for wheel radius! I used 0.328, 0.340, and 0.358 meters. I also dropped the hub and spoke weight since they contribute so little to rotational inertia, yield moments of inertia of .326, .369, and .427 Km * m^2, hugely different from Keith's erroneous numbers. The percentage change is -11.7 and +15.7 compared to Keith's -11.9 and +18.9. Notice how Keith's numbers are biased against 29 and in favor of 650B? Not that it matters since moment of inertia is irrelevant… Last, physics tells us that rotational and translational kinetic energy of a rolling wheel must be the same yet Keith's are wildly different. Now we know why, he botched the moment of inertia estimate by a factor of 3.7x! His total Ek numbers should be 383, 399, and 413 Joules, not 694, 730, and 779 J. The difference is -4% and +3.5%, same as the wheel weight. Why? Because radius doesn't matter. I didn't bother to see how Keith arrived his flawed answer so perhaps he did adjust for angular velocity but just did it wrong. I'm curious, Jim, did you make the same mistakes Keith made?

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