## Saturday, November 24, 2007

### Wheel Rotational Inertia Testing - 3

The wheels we tested had a pretty close range on inertia's so I doubt its going to make that much of a difference. Yet, I have to say that Dave is a CAT 3 racer and he has had some solid results for the past 4 years with the FSA's. So I'm wondering what the test results show for those wheels. How to Interpret the Resulsts : Since we have only the rear wheels, you might be thinking what the number represents. Rotational inertia or moment of inertia is the rotational analogue of mass in the linear F = m.a equation.

So according to what I believe (I could be wrong), more inertia means more of the mass of the wheel is concentrated around the rim as opposed to the center. When that happens, the wheel can be a little more sluggish at acceleration than a wheel with a considerably lower inertia. But again, only starts, stops and accelerating while racing count, otherwise I don't think moment of inertia hardly makes a difference. On flats at constant speed, aerodynamics has far more advantages than wheel weight. On long climbs with a grade of 3% or higher, wheel weight can factor into the speed you can attain for the same power input, so unless you're doing super long steep climbs on races, one doesn't have to worry about inertia.

Besides, when you take something on a climb that rolls, its generally agreed that its just overall mass that matters, not really on how that mass is distributed. One can do as much number crunching as he or she wants, but I warn you that you'll be dealing with extremely low numbers and you'll at once understand why the differences are so small as to be negligeble.

What's Next? I hope to test the corresponding front wheels, retest the Jets, and also form some kind of error analysis, because I fully understand this is not the most accurate way. For example, the final result could be affected more due to error in some parameters (as opposed to others) such as the distance from the ceiling to the center of the wheel. Again, if time allows me to do this, I'll come up with something. Sayanara!