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Question about Hub Bearings: What causes a bad bearing to cause the wheel to move incorrectly?

I was changing my hub bearings over the weekend and was wondering out of curiosity what exactly makes a bad bearing assembly cause the wheel to wobble a bit. When I checked the bearing with the wheel, there was noticeable freedom in movement in all the wrong ways, and the deep wirring sound as I drove down the highway confirmed it was my bearings.

I take the wheel and caliper off and then just for the hell of it check the assembly for give and take again. Now, the rotor seems solid. No give in the rotation at all. Take the rotor off and, again, the main assembly seems solid with no rotation besides the obvious turning of the axle itself, albeit a little noisy due to the bad bearings within. No clicking or anything either when I pull and push against the other rotational directions. I put the new assembly on, screw everything back together with all the torque specs and then confirm that the new hub assembly did indeed fix the problem at hand.

So, what exactly are the mechanics behind this? Why does it seem the wheel has some give to it when a hub bearing assembly goes bad even though all the other parts that are connected to the hub by themselves don’t?

You get more leverage when you check the bearing with the wheel installed. So it’s easier to test for bogus bearing movement with the wheel installed, especially when testing for rocking , where you hold your hands at noon and 6 o’clock or the 3 and 9 o’clock.