Can Someone Explain Road Force?

[bobstoc]

I have an '01 gs430 which has had a vibration and sometimes unsteady feel at highway speed (much like many others, I guess). The car had 16" stock wheels with Gooyears which developed feathering wear after 12000 miles. The dealer suggested new tires and alignment which led me to buy 2006 17" lexus Gs3 wheels with Dunlops and I had a 4 wheel align. After approx. 1000 miles, the Dunlops are developing feathering and the ride is still vibrating. Dealer checked entire suspension (for fourth time) and found all in order.

Dealer did road force test which showed the fronts at 34/24 and the rears at 15/18. I was told 34 is FAILING. What do these numbers mean? And what is causing it?

[mehullica]

Basically it is the high spot of the tire that would cause a vibration since the tire is not round. Matching the high spot of the tire to the low spot on the wheel reduces road force variation and is measured in lbs. Anything over 12 lbs will cause some abnormal feel in the vehicle. Your tires are way over and I would have them matched for a smoother ride. Do you have an alignment printout? What are the angles?

[bobstoc]

I don't have the printout but I when I had the dealer do an alignment (again), they said it was "off by 3 degrees". I'm not sure if they meant toe in. They stated this probably wouldn't be the cause. How is it possible two sets of tires wore unevenly if there is "nothing wrong with the vehicle". Do GS's typically chew up tires?

[mehullica]

Without the alignment angles, it's impossible to tell what is the problem. I'd run 40psi in the tires (cold) and rotate every 5000 miles. See if you can get a printout and post the angles.