Wheel moment of inertia estimate

[uwaeve]

Is there a "rule of thumb" that can be used to estimate the moment of inertia of a wheel? The information available is: wheel weight, wheel diameter, wheel width. Doesn't have to be exact or model-specific. Just trying to get a formula that's better than assuming a solid cylinder, shell cylinder, or thick shell cylinder. Also, the same goes for tires.

Specifically concerned with aftermarket race wheels for production cars like Porsches or Corvettes. More specifically, the types of wheels made by companies like BBS or OZ Racing. Any help is appreciated, since only wheel weight is typically reported.

uwaeve

 

[Warpspeed]

About all you can do is attach said wheel to a soft torsion bar and start it rocking (lightly by hand) back and forth like the balance wheel in a watch.

Some measurement and calculation will then give you a figure for moment of inertia.

 

[GregLocock]

Get a drawing of a typical wheel and work it out. It is not rocket science.

For an even cruder estimate, obviously the 'average' radius of the material is greater than 0 and less than the rim radius. So choose a figure somewhat less than the rim radius , say 80% and work it out from there.

Alternatively if you have a solid model of the wheel most solid modelling programs will tell you the answer.

For the tyre you will not be far wrong if you think about it as a total of three rings - two sidewalls and the tread.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[NormPeterson]

Two rings for the wheel, one for the barrel and the other for the center, with an estimate of how the mass is divided between them based on the given nominal wheel dimensions?

Norm

 

[jslat]

If you have the possibility to hang the wheel as a pendulum, in two cables, knowing the length from the wheel axis to the attachment point, you can easily derive the inertia from the small angle pendulum oscillation time.
The problem is to hang the tire so the pendelum point is the wheel axis.


Jesper Slattengren

http://www.prattmiller.com

 

[mloew]

If you are purchasing this as an OEM, this information is typically on the drawings or other document. You should request this information from the vendor.

Greg gave a good suggestion to figure it out. I would take it a step further and obtain a "typical" public domain or calculated information for both the mass and rotational inertia. Because mass and rotational inertia are related to each other through a parameter called the radius of gyration, you can take a published or calculated value for this and use your mass to obtain a better estimate for rotational inertia.

Best regards,

Matthew Ian Loew


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