I recently replaced the bearing in my whirlpool cabrio top loading washer. I got to thinking and had no idea which would be safer for the bearing. On one end it's a greater load on the washer, but on the other end you are rotating the bearing more times.

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    This is a classic question of tribology - the study of friction and wear. Jaspers answer below illustrates how the effect of load on lifetime can sometimes be nonlinear and nonintuitive. – aaron Mar 16 '15 at 6:53

Any size you like so long as you are not overloading the machine. Limit the loads to the size the machine is designed for, but don't engage in only running the smallest possible load for no good reason; this isn't a good reason. But don't load 20 lbs of clothes if the manual says 15 is the limit.

That being said, smaller load with more rotations suits most bearings better.

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Bearings tend to wear out as a result of repeated cyclical loads. As a rule of thumb, based on fatigue failure of metals:

The damage done by a single cycle of a load is proportional to the load raised to the power of 3 or 3.3. When the total of the damage done reaches some threshold, the part will fail. The threshold cannot quite be predicted in advance. For example:

  • If a bearing can handle 1,000,000 cycles of a 5 pound-force load, it can handle
  • 100,000 cycles of a 10 pound-force load, or
  • 50,000 cycles of a 10 pound-force load plus 500,000 cycles of a 5 pound-force load, or
  • 10,000 cycles of a 20 pound-force load, or
  • 1,000 cycles of an 40 pound-force load, or
  • 250,000 cycles of a 5 pound-force load, 25,000 cycles of a 10 pound-force load, 2,500 cycles of a 20 pound-force load, and 250 cycles of a 40 pound-force load.

Each time the bearing turns while subject to an eccentric load counts as a "cycle". Thus, washing one load of clothes can cause hundreds of cycles of damage to the bearings.

The Timken Engineering Manual has more details.

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