Quote:
Originally Posted by Johnny Danger
I disagree with you assertion . Ultimately, it comes to reducing unsprung weight and rotational mass. If the overall circumference is consistent, regardless of diameter the the lighter wheel will create less inertia .
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Disagree or not, physics shows that with all else being equal (same tire circumference, same width, same rim style & density), the larger rim setup will have a larger rotational mass.
Most of the tires mass is on the tread (which diameter & weight doesn't change with rim size). Most of the mass of the rim is the on the circumference of the rim (which does change with rim size). Moving this large weight farther from the axis has an effect on the rotational mass. More of the weight differences comes from the metal rim vs the rubber tire changes.
I have enclosed a simple display of this from a 3D modeling program. The units are converted to simple rotational mass, but they show the comparison of an 16x8 rim with a 25" diameter tire to an 18x8 rim with a 25" diameter tire. This is a good test for our Boxsters.
The 18" rim setup shows a 23% increase in effective mass of the wheels, even though the overall circumference of the wheels stays the same.
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