Tires: Tire balance, center hub, static balance

Question
I have a static bubble balancer. Do I have to put weights on both sides of the tire. When I put weight on just one side, the bubble is centered, but the tire shakes about 60mph. Also, why do you have to put weight on both sides and how do you determine where to put the wight on the inside of the tire?

Answer
Sophie,

There are many things that can cause a wheel end vibration, but only two of these are directly related to tires - balance and uniformity.

Before we get into the tire items, let me list some of the other items:

Off center mounting of the tire to the rim
Off center mounting of the rim to the hub
Off center hub.
Out of balance rotors and other rotating components
There are others

Balance (which is really both a tire and a rim item) is merely distributing the weight so it is even around the circumference.  In effect, the balance weight is sized and placed such that it compensates for the uneven mass distribution of the rim and tire.

Static balance (bubble balance) only compensates for the circumferential component.  My estimate is that this takes care of 50% of the problem.

Dynamic balance also compensates for the side to side (or off center) component.  I think this takes care of 30% more (for a total of 80%)

So when you use a bubble balancer, putting half the weight on one side and half the weight on the other side compensates for mass in the center.  Putting the weight all on the outside (or inside) is like compsenating for the mass being highly off center (an unlikely situation).

But what if the wheel is slightly cocked?  Then dynamic balancing will compensate for this and the weights would be placed accordingly.

The last tire related item is uniformity, which I think is the last 20% - split 5% wheel, 15% tire.  The best way to look at this is "out of round", however this term isn't 100% accurate.  Uniformity is more closely related to deflection variation of the loaded tire.

This means that even a perfectly balanced rim and tire assembly might cause a vibration.  Since the tire is mounted on the rim:  the rim could be the cause, the tire could be the cuase, or it could be a combination of the 2.  In fact some vehicle manufacturers require the tire and rim manufacturers to mark their components and then the vehicle assembly plants match these marks to produce a more uniform assembly.

Since all you have is a bubble balancer, you have a limitation of what you can do.  So the best thing is to split the weight even inside to outside, as though the offending mass is in the center of the tread.

Hope this helps.