I recently replaced the factory Goodyear LS with a slightly larger tire. I purchased a set of Kumhos 265/60s which really improved the handling (very noisy) but I noticed the steering wheel vibrated at 50 mph. After three trips back to the tire store they agreed to replace the tires and I went with Geolanders in the same size. Same problem, wheel shimmy at 50 mph. The replaced those tires with another set of Kumhos and had the same problem. I took it to the dealer and had them rebalance the tires and align all four wheels ($210). The vibration was worse than before. I took the car back to the same tire dealer and they installed another set of Geolanders on it. This makes my fourth set and the steering wheel stills has the shimmy in it at 55mph. The tires have been road forced balanced (12, 11, 6, & 9- all within Nissan's spec). I'm out of ideas and patience. Anyone have any idea what I need to do next? The car has never been in a wreck and the old GYs, while not great tires, rode smooth with no vibration. Looking for help on this one.