An Effective Rotational Mass Database for Wheels

moiThanks to Adrien Gontier of Roues Artisanales and David Linke, I am able to provide you with a unique database of moments-of-inertia and effective rotational masses of a large number of wheelsets. The data allows greater accuracy for VE, a virtual elevation perl script I wrote.

The big surprise is that the larger wheels contribute more than 2kgs to the inertia of the rider and bike. While it’s not going to make or break the VE calculation, it will add an increment — however small — to the accuracy of the calculation.

For Virtual Elevation work, the database can be used to provide the effective rotation mass of the wheels, ERM,   to correct the inertia term in Newton’s Second Law, thus:

F – Crr m g cos(theta) – CdA * rho v^2 / 2 – m g sin(theta) = ( m + ERM ) a

MOI in itself may have limited impact on climbing or time-trialing consideration, but may be useful in teasing out more useful elevation data to estimate Crr and CdA.

[Edit: Thanks to Dan Connelly for providing a correction to the spreadsheet in column E, and for adding a rotation to translation ratio in column J. ]

Download the spreadsheet here.

In a subsequent post, I’ll try to quantify the impact of effective rotational mass on the virtual elevation profiles.

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