The rumors about the bearings that I heard was the switch was done to reduce damage during shipping. Ball bearings, having the near point contact to the races that they do, tend to sustain damage when hit with a sharp jar when they are not moving. Shipping vehicles by rail aggrivated that so when roller bearings became cheap to manufacture they were switched. Roller bearings also seem to stand up better to poor lubrication.

Ball bearings work just fine and seem to last about the same number of miles as rollers as long as you don't hit curbs and jump railroad tracks all the time. Many modern cars still use rollers, including BMW. They do offer less rolling resistance. The rear bearings on my BMW 325i are double row sealed balls, and they support disk brakes and the rear axle half shafts. I have only had to replace one of them in 165k miles because of a curb impact that also bent a rim.

You can buy several sets of ball bearings for the same price as one of the conversion kits.

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