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Old 04-21-2010, 09:38 AM
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PaleMelanesian PaleMelanesian is offline
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Join Date: Jan 2007
Vehicles: 2009 Fit, 2004 Odyssey, 96 Civic retired
Location: Longview, TX
Posts: 14,035
Re: One reason for the 2011 Cruze’s excellent fuel economy is its wheels

I'm ignoring the spokes vs rubber sidewall tradeoff. The rubber is likely slightly lighter than metal alloy, but I'm not sure how much.

Think of where the mass of the rim is. It's mostly out on the edge, like a donut, away from the centerline. The rotational inertia for a donut is a function of the radius CUBED. Looking at just this rim, changing from 16" to 17" is 20% worse inertia. In addition, there's the extra mass needed to create the larger rim.

6% more rim mass, but probably more if it's wider as well.
20% more rotational inertia, resisting any acceleration/braking efforts.

compared to a 14", it's 79% worse, or nearly double.
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