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, Sat, 5 Feb 2005 09:51:34
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Rotational inertia works in principal the same way that linear inertia works, like moving a heavier car in a straight line takes more energy input to move it at the same acceleration as a lighter one.
The formula for rotational inertia is I=MR^2, I=Inertia M=Mass R=Radius. There is a constant one multiplies by to take in to account diffenent rotating objects (Like a thin walled cylinder, vs. solid cylinder, vs a rod rotated at its center, etc).
Inertia of a rotating object increases proportional to its mass increase, but proportional to the square of its radius' increase, so upping wheel size has a greater effect at extreme sizes than mass increase, which is whyu when going to very large wheel sizes weight is very inportant, especially ther weight of the rim itself, since the mass the furthest outwards from the center of the wheel has the greatest influence on inertia.
On the same note, thinner lighter tires make a difenerence in inertia of a rotating wheel as well, since their mass is concentrated even farther outwards than the surface of the wheel.
Hope this helps. By the way I am running 15" Inca's on my project 900T since they are smaller radius and are an extremely light alloy to start with, they weigh about 15lb by themselves with no tires, and the magnesium racing wheels on my Dad's '66 Morris Mini Cooper S are 10" diameter, and weight 7lb!
This effect is exactly why lightened flywheels have such an effect on an engines performance, less energy input is lost to changing the inertia of the flywheel so that energy is free to go to the wheels, resulting in slightly more WHP and quicker engine response.
Drew
posted by 66.74.1...
, Sat, 5 Feb 2005 09:51:34, Sat, 5 Feb 2005 14:42:33
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