Living the High (Precision) Life - Does Better Precision Equal Better Bearings?

Does Better Precision Equal Better Bearings?  Not necessarily, and it depends on your application and your performance requirements.

Precision bearings are manufactured to meet or exceed recognized and published local (DIN, JIS, ABEC) and international standards (ISO) to insure conformity and interchangeability.  Several precision classes, or tolerance ranges, are defined in these standards, as shown in the infographic above.

These tolerance classes control dimensions and shapes of the rings only, not the quality of the finish bearing.  Of primary concern for the user, the specifications control the variation in bore, outside diameter (OD), and width, with higher requirements on the bore and outside diameter because of their affect on mounting and internal clearance.  The other primary concern is runout of the rings, a specification that affects tracking, noise, and vibration of the operating equipment.

1. Verify your bearings meet the minimum precision class for the application - this may seem intuitive, but it's important to note because of the availability of counterfeit, non-precision, and surplus bearings.  Know the specification and know what you are buying.  A standard precision ball bearing in a centrifuge or a standard precision angular contact bearing in spindle can have disastrous results in a short period of time.  Additionally, bearings from surplus (eBay, Alibaba), counterfeit, and even non-precision manufacturers may not meet the minimum PN (P0) requirements and you are left to find out the hard way. 
2. Using a higher precision bearing will not directly increase bearing life - experiencing bearing issues?  Premature failures?  Excessive noise and vibration?  Catastrophic failures?  Switching from a PN bearing to a P5 bearing won't fix your problems, but it would be a more expensive way of having the same problems.  
3. Runout - one of the critical improvements of precision bearings, runout has an effect on noise and vibration, tracking, as well as balancing.  Super precision spindle bearings from manufacturers like SKF, FAG, and Timken usually feature P4 ring tolerances with P2 runout. 
4. Internal clearance and preload - specifically for super precision bearings (P4, P4S, P2, SP, UP), the bearing bore, OD, and width can impact the preload or clearance in the mounted, or assembled, bearing.
5. Shaft and housing condition and shape