For those who don't know what this is all about:
We are all familiar with balancing a tire assembly (tire mounted on a rim). That's the result of imperfections in the mass distribution of both the wheel and/or tire.
Static balance assumes the imperfection is more or less centered laterally (inside to outside) That's probably OK for about 50% of the assemblies.
Dynamic balance locates where an off-center weight is needed so that there isn't any lateral (side to side) imbalance. The would cause a wobble.
Both of the above are mass distribution problems. But there is another problem - run out!
Well, not exactly. It's really uniformity, which is a combination of runout and variations in stiffness. Wheels only have runout, but tires have both.
If you match the low point of the wheel with the high point of the tire, you get a "rounder" assembly. (and, again, not exactly. It's actually the high point (or low point) of the first harmonic, but most everyone kind of ignores that detail.)
This is not new. 45 years ago, I saw my first machine in the tire factory that measured tire uniformity - and I don't know when car manufacturers started match mounting, but it was at least 35 years ago. But it required some sophisticated (and expensive) equipment. Needless to say, both the tire manufacturer and the wheel manufacturer had to mark their products in order to make the whole thing work.
About 25 years ago, I first became aware that Hunter Engineering had a balancer that also measured uniformity. It did so in a rather crude way, but it was the only shop level machine capable of doing so. Hunter referred to this as "Road Force" and the name has kind of stuck.
There are a number of problems with the Hunter unit - one of them being that you have to take the assembly off the balancer and back to the mounter in order to reposition the tire relative to the wheel to get a better uniformity value. This Corghi unit attempts to address that issue by having the uniformity measured at the mounter. Unfortunately - as was pointed out above - the assembly still has to go to the balancer to be balanced.
There are similar problems with the Corghi unit that the Hunter unit has - and that is the size of the measuring wheel. Because the road is flat and the measuring wheel is round, the way a tire reacts to the road isn't well simulated - and the smaller the wheel, the worse this is.
The uniformity machines in tire factories use a 30 inch diameter wheel - AND - they reject any assemblies over a certain value. That leaves only false positive tires in the mix. The theory is that the consumer will find those few false positives - and those become warranty claims, so the size of the problem can be quantified and adjusted if needed.
The early Hunter units had a 7" diameter wheel, but very quickly discovered that this wasn't good enough so they now have a 14" diameter wheel. It appears that the Corghi units are smaller than 14". And even with a 14" diameter wheel (or even a 30" diameter!) there can be false positives and false negatives (assemblies that are bad that appear OK, and vice versa.) For that reason, tire manufacturers do not accept returns based on "Road Force" values alone!
I note that in the Corghi video, they match the tire with the vale hole in the wheel. I can not emphasize this enough:
TYPICALLY WHEELS AREN'T MARKED FOR RUN OUT LOW POINT BY THE VALVE HOLE!
Some are, but typically not. And there is no way to tell without measuring the wheel. Please note: There is no harm done by doing so, but it may not be doing anything of value. If I were mounting tires, I would use the valve hole, but I would recognize the situation.
Also, many tires are NOT marked for high point. If the tire isn't marked, you can't tell where the high point is without measuring it.
In summary: Assemblies that are balanced might by out of round - and match mounting doesn't replace balancing. An assembly has to be both sort of balanced and sort of round to not have a vibration.
