Wheel Balance

[catiaguy12]

Guys! I need help...

How can I calculate the static unbalance of a wheel from the cad data?

Thanks!

 

[Fabrico]

What imbalance? The valve stem hole?

 

[GregLocock]

Nice catch, just multiply the radius of the calculated CG from the nominal axis of the wheel by the mass of the wheel.

I suspect Fabrico is implying that your CAD model will not show any signifiant out of balance, as it is primarily due to thickness variations away from nominal. Plus the valve hole.



Cheers

Greg Locock

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

 

[NormPeterson]

Or it could be for an unusual wheel design with nonuniform spoke spacing and/or unequal spoke mass/mass distribution. The so-called "Teddy Bear" wheels that were available a few years ago come to mind.


Norm

 

[catiaguy12]

Hi Greg -did that. but the amount was too large.

e.g.

mass of the part 18.4 kg
C.G. X=57.93mm
Y= 0.227mm
Z=-0.019mm

Geometrical axis is "x", which is going thru the pilot bore.
Radius of C.G.=0.228


Static unblance= 4.19kg-mm

Is this correct?

Now, I want correlate this with a static balancer using a correction radius of 230.00mm, any ideas?

Thanks! Greg

 

[Fabrico]

Sounds like you either need to re-align point "A" in the machining process, increase the number of surfaces machined, or re-evaluate the casting.

 

[catiaguy12]

Good idea! Thank you

 

[Xwheelguy]

Fabrico,

It's a 3D model, not a physical part. The numbers he has would be from a perfectly nominal wheel if it were cast and machined, so there really isn't much he can do to improve these numbers, unless the wheel is an asymmetric design or he really screwed up while modeling, or his material properties are way off in the CAD software.

Greg,

An 18.4 kg wheel???? Is this an aluminum wheel???? What's the diameter? Has to be over 20 inches and quite beefy, I would think, unless you're analyzing a casting or making a wheel for a large vehicle like an aircraft, dump truck, diesel semi-truck, etc. or your chosen material density is way off base in the CAD software.

Are you making this calculation with the valve hole removed from the model? If so, then remember, the imbalance will be checked with a valve stem installed at the assembly plant (if the wheel is going to an automaker), so either supress the valve hole subtraction or add a valve stem to your part for the sake of accuracy and more "real world" numbers.

We typically just ask for the weight of the valve stem from the customer, then model a sphere with the center of the sphere being at the center of the valve stem (intersect the centerline of the valve hole with either the angled surface on the tire side of the rim where the valve is drilled OR the spotface on the tire side of the valve). We increase the diameter of the sphere until we reach the same mass as the valve, then unite the sphere with the wheel for the added weight. Optimal conditions would be to have a model of the actual rubber valve stem or tire pressure monitor/valve stem combination. Feel free to email me if you need clarification on the area I'm describing.

This isn't to say our chosen method is perfect or the best way to do it...it just works for us and has resulted in decent quality in terms of predicting physical part balance in a mass production situation.

I hope at least some of this info proves useful. Not enough information on wheels and tires is publicly available and I feel it would greatly improve the industry if we were to share techniques for things like this, including anything related to FEA simulations for rotary fatigue, radial fatigue and impact analysis.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[NormPeterson]

I think that using units involving kg instead of g are making things sound much worse than they are.

Static unblance= 4.19kg-mm
Is this correct?
Now, I want correlate this with a static balancer using a correction radius of 230.00mm, any ideas?

4.19 kg-m = 4.19 g-m = 5.8 oz-in
About 5/8 oz on a 9" radius unless I've done something rather stupid.
17" wheel? Steel?


Norm

 

[GregLocock]

That's right, 4190/230= a 10g weight on each flange. The smallest we bother with!

Cheers

Greg Locock

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

 

[NormPeterson]

On edit for the obvious stupidity . . . failure to correctly copy that which was right in front of my eyes. Arrrghh.

4.19 kg-mm = 4.19 g-m = 5.8 oz-in

 

[catiaguy12]

Thank you guys!

Here is my problem, I'm working on a wheel that will be fitted with a presure sensor on the drop-well area, and after the part is fitted with it the balance goes up. So, I'm thinking about a counter-weight at specififed radius.

With the explanation you guys have given me, now I’m confident enough to calculate the counterweight mass.

Thanks!