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i want to find the equivalent mass of a car rotating parts and i came across this site which provides some cars formula : http://www.thecartech.com/subjects/auto_eng/car_performance_formulas.htm

So far i understand almost everything until i get to the part where inertia resistance is calculated as an equivalent mass of rotating parts. Here is the quote :

meq= equivalent mass of rotating parts [kg]

= [Iw (1/rw)2 + Ip hf (if /rw)2 + Ie ht (if ig / rw)2]

where:

Iw= polar moment of inertia of wheels and axles ≈ 2.7 [kg m2]

Ip= polar moment of inertia of propeller shaft ≈ 0.05 [kg m2]

Ie= polar moment of inertia of engine ≈ 0.2 [kg/m2] + polar moment of inertia of flywheel and clutch ≈ 0.5 [kg m2]

hf= mechanical efficiency of final drive

ht= mechanical efficiency of transmission system (hg x hf)

ig= gearbox reduction ratio [ig1 or ig2 or ………….]

if= final drive reduction ratio

rw= tire radius [m]

Now what i dont understand is the first part :Iw (1/rw)2 ???

Why do we divide 1 by the wheel radius?? is this a mistyping mistake??

Can someone explain this to me please?

Thanks !!

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# I Equivalent mass of rotating parts

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