Well things have gotten very interesting.

First off, go to http://www.gsp9700.com/pub/search/findgsp9700.cfm to find the shop near you that has a Hunter 9700. It appears to be the standard for most big dealerships. My local Dodge place has one.

As I understand it, wheels shake because they have some combination of uneven weight distribution, uneven shape (out of round or wobble) and uneven stiffness. The vehicle 'rides up' on the stiff spots, and this changes the effective the radius of the tire as it rolls under load. The Hunter machine diagnoses all of the factors, and by compressing the tire with a loading roller, measures the amount of force the tire generates as its non-uniformity 'pushes back' against the machine.

So, now the results for my truck : All 4 tires are out of whack. The machine recorded 3 of the 4 tires at 22 pounds-force, and one at 39 pounds-force. The tech said he broke the beads, applied the corrections as best he could, and still came up with high-normal readings on 3 tires and a high reading on #4. I am going to confirm tomorrow morning that these readings were 'after corrections', and as best as he could get. The summary on my invoice starts with "4 TIRES WILL NOT BALANCE ON ROAD FORCE"

Certain vehicles are more sensitive than others, but my shop considers anything above 12# force to be enough to cause ride quality issues. The Hunter website has a higher threshold for trucks, about 26#.

http://www.gsp9700.com/pub/technical/limits.cfm

Now our trucks are pretty 'stiff'...big axles and springs, a very rigid frame, and with an empty bed, almost no damping weight on the rear end. Intuitively, I would think this would make the truck more sensitive.

According to the dealer, there is nothing left to do but replace the tires. I talked to the shop that sold me the tires, and they of course have never had such a problem with these tires (National Commando's built by Cooper). But I presented the evidence, and he agreed to replace them.

So I have one more round of visits to make tomorrow. First, I am going to confirm that the dealer applied corrections and still couldn't get the tires within spec. I'm going to roll in with a printout of the Force Limits above, and ask them how that relates my results. Assuming everything is on the level, I'm off to the tire dealer to get some fresh tires. I'm going with a different brand however, if all 4 tires are out of spec, I'm not big on replacing them with 4 of the same.

I hope this helps others with similar problems! After reading up, there is no substitute for road force balancing. It's done from the factory on high-tech equipment, and many smaller tire shops like mine don't have the expensive 9700 machines. Spin balancing is only a part of the solution. Of course at $100 a pop, I hope I don't have to go through this again.

What do you guys think? Am I within my rights to :

1) Ask the tire shop to foot some of the bill for my $100 diagnostic test that proved what I already knew (the truck shakes), since it's due to the defective tires they sold me?

2) Ask the dealer to road-force my new set to confirm the problem is fixed, without another charge?

I will update tomorrow...

**EDIT** another very informative video - http://www.youtube.com/watch?v=efhgM2TcQpI

I swear I don't work for this company...but this thing looks sweet. I want one.