Actually wear on the wheel bearings can be caused by larger tires. Going around a corner you are putting lateral torque on the bearing. As you corner, the wheel will want to do this \ and the larger the tire, the more it will want to do that. That bearing is what keeps the wheels from doing that. At 30K, its about time for them to be check and repacked. Its not really torque, its moment about the center of that bearing, its similar to torque. The longer lever (taller the tire, the radius of it will be the lever arm) the more moment (torque) can be applied. Yes, these bearings are hardened steel, but theres just that possibility. Im probably totally off here, but I can see in my head how this works. Enough cornering force and you could stretch the threads that hold the bearing plate in place. On my rodeo this plate was no more than a 1/4" and were fine threads, but it could happen. When manufacturers design components they do so based on tire sizes, optional and standard. They design for the bigger tire size and when they put the smaller tire on, the design will actually have a higher factor of saftey. This factor of safety is what determines when a piece should fail. It takes into account for wear, sudden impacts and some things you might not expect. When I designed my control arms, i designed them with a factor of saftey of 3, meaning they would fail at approximately 3 times their rated load. My experiences have always been that 2wd bearings are smaller in diameter than 4wd bearings. That doesnt always make them weak, but it increases the lever arm, allowing more torque to be applied to that bearing. Imagine a lever from the bottom of the tire, to outer edge of the bearing. Its not very hard to get a few hundred ft lbs of torque on there by hand, imagine a vehicle with about 1000 pounds on that tire. Now imagine say 750 pounds pushing on the bottom of the tire towards the inside, and multiply that by say 15" and you have 937.5 ft-lbs of torque on that bearing. Now with a 29" tire you will have about 850ft-lbs. With that tire that is 3" taller you added almost 100 ft-lbs of torque. That will most definitely causes extra wear on a bearing. Again, I may be totally wrong here, but this is what I've been tought in classes and it makes sense to me.

Dan