Friday, November 23, 2007

Wheel Rotational Inertia Testing - 1

The day before Thanksgiving was one spent with our wheels, since we SOO had nothing else to do. Getting a break from the university can also be a boring time for students.

A friend of mine, Dave Kina, and I sought out to investigate what the moment of inertias would be for some rear wheels we had. We raided his grandma's basement, which is sort of Dave's cycling playground, with couple of bikes, a pool table with hundreds of cycling items, weights, shoes and what not. The overhead pipes gave us a nice support from which we could do the tests.

We chose rear because, well, we didn't have time for the front ones, and we aim to test them at a later time.

The test setup was a simple pendulum, we hung our wheels from the ceiling using a rope for hanging clothes. The setup is described on analytic cycling in the wheels and inertia section, so I'll spare you the details.

We weighed the wheels with the Ultimate Digital Scale. The wheels had everything on them in as ridden condition except for the QR skewers since that's not rotational.

We timed 100 swings with two stop watches, a Suunto and a Polar. We then averaged those two times out, and divided it by 100 to get the the average time per swing, or the TIME period of the pendulum. This is our Tau or T in the equation :

We measured the vertical distance from the ceiling and that was our r0, or r not.

We then simply solve for Io, or Io, which is the moment of inertia of the pendulum about the ceiling support. The second equation relates the rotational inertia about the ceiling with that about the CG of the wheels which is Ic, so we used that to arrive at what we wanted. Instead of plugging in all the numbers on our calculators, we just saved time and plugged it into the calculators on analytic cycling. The results are on Part 2.

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