Static balances top to bottom as the tyre appears on the car and can be done using a bubble balance. It will correct balance problems that cause the wheel to bounce up and down and it is the most common problem.
Dynamic balances side to side/top to bottom error that can cause the tyre to wobble. That is the top of the wheel may have more weight on the inside and the bottom more weight on the outside. It is generally less of a problem but it is still a real problem. (If you want to have fun with this idea, try adding weight to on the top right side of a yo-yo and an equal weight on the bottom left. It will remain in static balance, but if your try to let it spin you will quickly see the problem.
What seems to be lacking or not fully appreciated in this conversation is that not all balancers (both human and mechanical parts) are created equal.
I was thinking that this thread had died - but I guess not.
Allow me to add my experience - which seems for some to be the only important thing.
I am an engineer for a major tire manufacturer. I used to be involved with what we called “Vehicle Senisitivity Studies”. These were studies - generally done with the cooperation of a vehicle manufacturer - that would explore what level of a particular property - like balance - would cause vehicle vibrations. Here’s what I’ve learned over a decade of doing these:
Most (emphasis on the word “most”) vehicles (and drivers) are tolerant of imbalance of 1/4 oz or 5 grams - the smallest balance weight increment available. This means that most of the time, the round off error built into balance machines doesn’t result in a detectable vibration difference. I have seen situations where 3/4 oz has not been detected.
Most vehicles are insensitive to lateral forces - relative to the tire’s footprint, this is side to side. This means that dynamic balancing generally has a minimal effect.
Some vehicles (and some drivers) are more sensitive than the norm - some much more!!! This means that some vehicles (and drivers) are going to need more than just static balancing in order to produce an acceptable ride. Some sre going to need more than dynamic balancing. And some of going to need more than can be done at the store level.
There are certain parts of the country where there are more ride complaints than others. Florida seems to be most sensitive. I don’t know if this is because of the population (age being a factor), the types of cars that are driven there (age might be a factor here as well!), or the smoothness of the road (the roads don’t experience freezing and the subsequent “ripples” and pavement break up). Clearly certain parts of the US generate very little complaints. When these sensitivity studies are conducted in the Detroit metro area (which is where many of the cars we borrowed were located), our ride evaluators sometimes had to search a while before they found a suitable road.
Even dynamically balanced tire and rim assemblies could generate ride distrubances due to “non-uniformity” - the term we tire guys use to describe the combination of “out of round” and “stiffness variation”.
I’ve concluded that if you are “in the business”, you have to have a Hunter GSP9700 Road Force machine - or an equivalent. The new version with the 14" diameter road force wheel are better than the old ones with the 7" diameter wheel. But they have limitations. For example, they are low speed machines, and tires can develop high speed vibration problems that aren’t detectable at low speeds.
But if you are doing it yourself - and are willing to put up with the occasional vibrating assembly - then bubble balancing is fine.
But when making generalizations based on your experience, you have to be very careful. If your experience doesn’t include places like Florida, or you don’t encounter cars or drivers who are sensitive, then you could, incorrectly, think that dynamic balancing isn’t needed - not to mention road force and those more exotic issues.
Bubble balancer = static balance only; sum of the forces about the wheel axis = 0. This only works well for skinny wheel/tire combos (like the old model-T’s or bicylce wheels)
Dynamic balancer will force the sum of the moments about the wheel axis to be zero. This is why weights are placed on both the inside and outside of the wheel. This is the only way to properly balance a modern wheel/tire.
The one thing I am is a major nitpicker. Speaking for myself, I DO notice a 1/4 ounce imbalance very easily and will not tolerate it.
As you mention, weights are in 1/4 ounce increments and if the balancer shows that 1.3 ounces is needed in a certain point then what? This means the guy doing the balancing SHOULD be pruning a bit off the end of a 1.5 to get it as close as possible to 1.3.
How many of you have ever seen any “snipped weights” on any of your wheels? Ever?
Your weights are always in 1/4 ounce increments; as in “close enough”. Right?
I snip weights down to the point I may take a 1/4 of the amount off of a 1/4 ounce weight (1/16 ounce basically).
The fact still remains I use a bubble balancer to rebalance many previously computer balanced tires and no, I do NOT put up with the occassional imbalance.
That’s interesting info, I agree that it is very dependent of the vehicle. I remember having an early 80 3-series (when they were new) that was extremely sensitive to from wheel balance, to the point the you really had to balance the wheels on the car to avoid shaking at specific speeds.
Some of you should keep in mind that bit about snipped weights.
Look at your own car, your neighbors, or all of the cars in the WalMart parking lot as you walk past and see how many show signs of being cut a tad.
Unless you believe that every tire that is balanced on every car automatically comes up on 1/4 ounce increments and there are no “in-betweens” of course.
Question for the people who think this stuff is dead-on. If the balancer shows you need 1.6 at a certain spot on the inside and 1.3 at a certain spot on the outside, which weights are you going to use and how are you going to apply them? Just curious.
(Remember, there are no 1.3 and 1.6 weights made; only .75, 1.0, 1.25, etc. with .25 being the lightest one.)
All I know is that back in the day when I balanced hundreds of tires in a week, the dynamic balancer we used worked greatwith most every tire except one company’s 500 make and it was nearly impossible to balance because it was just a piece of junk. Another manufacturer who had an Italian name that started with a P had tires with so little runout that I seldom had to use more than a 1/4 ounce to get them into balance.
