Basic Dynamic Load Rating Bearing Life vs Stress Based Bearing Life
When engineers choose bearings for an application, they usually look at key factors like:
- Basic dynamic load rating
- Speed limits
- Alignment (both dynamic and static)
- Thrust load capacity
- Price
Let’s break down what these mean—starting with the most important one: basic dynamic load rating.
What Is Basic Dynamic Load Rating?
The basic dynamic load rating tells you how much load a bearing can handle while still offering a long life. In general, the higher the rating, the longer the bearing will last, assuming everything else stays the same.
But not all bearings are built the same. To compare them, engineers use a standard formula developed by organizations like ABMA and ISO:
Bearing Life Formula (L10)
This formula estimates how long a bearing will last under specific conditions. “L10” means that 90% of bearings will last at least this long, while 10% may fail due to wear (specifically, raceway spalling).
It's also easy to compare bearings from different manufacturers with the L10 formula. But it has a limitation: it assumes a condition of stress in the raceways of the bearing with a given C1 rating and an applied Pe load.
How Is the Load Rating Calculated?
To figure out the C1 rating, engineers use another formula:
Why Bearing Design Matters
A bearing’s lifespan depends on how much stress it experiences under load. So, even if two bearings have the same load rating, their actual performance and lifespan can vary based on design. Manufacturers use the fcm factor to calculate the basic dynamic rating for any bearing. If a catalog shows a rating higher than what the geometry suggests, the manufacturer is increasing the fcm value. Lab testing might back this up. But sometimes it's overstated.
Bearing Performance: A Real-World Comparison
The following tables show the PT Select P2B207 bearing ranked third in cataloged ratings. But when tested under load, it had the lowest stress and handled the load better than six other brands.
| Bearing Description | Catalog Basic Dynamic Load Rating (lbs) | Ranking |
|---|---|---|
| PT Select P2B207 | 38,400 | 3 |
| Competitor A | 33,300 | 6 |
| Competitor B | 39,000 | 2 |
| Competitor C | 37,090 | 5 |
| Competitor D | 33,300 | 6 |
| Competitor E | 46,400 | 1 |
| Competitor F | 38,300 | 4 |
| Bearing Description |
Heavy Load 25% Ca Rating |
Light Load 7% Ca Rating |
Combined Load Fa/Ft = 1 |
Thrust Load 10% C1 |
|||||
|---|---|---|---|---|---|---|---|---|---|
| psi | Rank | psi | Rank | psi | Rank | psi | Rank | Sub-Ranking | |
| PT Select P2B207 | -326,552 | 1 | -223,537 | 1 | -317,049 | 1 | -326,274 | 2 | 2 |
| Competitor A | -335,743 | 6 | ,234,175 | 6 | -333,358 | 7 | -360,674 | 7 | 1,764 |
| Competitor B | -332,619 | 5 | -231,699 | 5 | -326,375 | 6 | -334,640 | 6 | 900 |
| Competitor C | -329,923 | 2 | -225,900 | 2 | -320,404 | 2 | -329,929 | 5 | 40 |
| Competitor D | -329,959 | 3 | -225,938 | 3 | -321,014 | 3 | -334,449 | 4 | 81 |
| Competitor E | -331,361 | 4 | -227,202 | 4 | -322,866 | 4 | -336,083 | 3 | 256 |
| Competitor F | -367,478 | 7 | -252,074 | 7 | -324,567 | 5 | -312,831 | 1 | 245 |
| Bearing Description |
Heavy Load 25% Ca Rating |
Light Load 7% Ca Rating |
Combined Load Fa/Ft = 1 |
Thrust Load 10% C1 |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| psi | Rank | psi | Rank | psi | Rank | psi | Rank | Sub-Ranking | Total Ranking | Final Rank | |
| PT Select P2B207 | -268,667 | 4 | -178,923 | 4 | -260,326 | 3 | -268,423 | 3 | 144 | 146 | 1 |
| Competitor A | -271,077 | 5 | -178,231 | 3 | -268,875 | 5 | -293,999 | 7 | 525 | 2,286 | 6 |
| Competitor B | -253,796 | 1 | -171,937 | 1 | -248,250 | 2 | -256,089 | 2 | 4 | 904 | 4 |
| Competitor C | -268,051 | 3 | -182,013 | 5 | -262,208 | 4 | -270,742 | 4 | 240 | 280 | 3 |
| Competitor D | -280,455 | 6 | -192,040 | 6 | -272,853 | 6 | -284,272 | 5 | 1,080 | 1,161 | 5 |
| Competitor E | -281,722 | 7 | -193,166 | 7 | -274,499 | 7 | -285,736 | 6 | 2,058 | 2,314 | 7 |
| Competitor F | -260,669 | 2 | -177,162 | 2 | -228,278 | 1 | -219,978 | 1 | 4 | 249 | 2 |
So, the real question is:
Would you choose a bearing with a higher catalog rating? Or one that performs better under stress, like Rexnord PT Select?
If you have questions or would like to talk to one of our application engineers about our PT Series for your high-temperature application, contact us below.
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Marlon Casey
Marlon Casey is an Engineering Manager with the Regal Rexnord Bearing Group. He has spent 11 years with Link-Belt and over 31 years with Rexnord managing the Research & Development, Testing, Engineering Analysis, Product Design & Development and Product Engineering activities. Marlon’s responsibilities include conceptualizing, developing, maintaining, and improving bearing products required to support MB, Link-Belt, REX and Filament Industrial Bearing products. His skillsets and vast experience are regularly utilized by the manufacturing, commercial, and applications’ departments to provide an expert level of product knowledge to support customer needs.
Page last updated: November 4, 2025