Background Information
NTN has strict standards regarding the cleanliness of the steel used in our bearings, with a maximum tolerance for non-metallic inclusions of 50 microns.

Why It Matters
Inclusions create weak spots in the steel that will fatigue at an accelerated rate causing fracturing and cracking. Even on a microscopic scale, these cracks will propagate and cause failure of the bearing.

Test Lab Results
Examination under a scanning electron microscope detected non-metallic inclusions in six competitor products were in excess of 200 microns in length, which is over 4x NTN’s maximum allowance for inclusions.

Background Information
After the forging and heat-treating, NTN’s bearings go through high-precision grinding, polishing and superfinishing, to achieve the smoothest surfaces and tightest tolerances possible.

This results in a low roughness average which allows for lower rolling resistance, decreased NVH, increased part life, higher load capacity, better sealing properties and a reduced break-in period.

Why It Matters
Raceway surface roughness leads to:

• Increased friction and heat
• Deformation of the components
• Abrasive contamination of the grease as the rolling elements wear down the rough surfaces

Test Lab Results
Gen 2 and 3 wheel bearing samples were within spec but only by a small margin. Gen 1 samples barely met NTN’s minimum hardness spec at the outboard inner ring, while the inboard inner and outer ring measurements fell well below spec. All samples showed a large amount of variation, indicating loose tolerances and poor quality control.

Background Information
The bearings were measured for hardness in various locations including the inboard and outboard portions of the inner ring as well as the outer ring.

Why It Matters
Hardness is critical in the life of a bearing. Components that fail to meet NTN’s minimum hardness spec will not have the longevity of properly heat treated components and under-hardened steel will result in uneven wear and premature failure.

Test Lab Results
Gen 2 and 3 wheel bearing samples were within spec but only by a small margin. Gen 1 samples barely met NTN’s minimum hardness spec at the outboard inner ring, while the inboard inner and outer ring measurements fell well below spec. All samples showed a large amount of variation, indicating loose tolerances and poor quality control.

Background Information
Uniform precision of the rolling elements within a bearing is critical. Uniform ball size is achieved through precision machining and meticulous quality control.

Why It Matters
The balls in a wheel bearing carry the full weight of the vehicle and it is very important that the balls are the same size so that load is evenly distributed. Variation in ball size will cause uneven wear on the raceway, and uneven loading throughout the other bearing components, causing fatigue and premature failure.

Test Lab Results
The ball size was observed to vary greatly between products, far exceeding NTN’s 1 micron tolerance for ball size variation. The Test Lab was able to conclude that this variance is caused by lack of precision during manufacturing and assembly and permitted by poor quality control.

Background Information
Designing and manufacturing the bearing cage requires careful engineering. The cage holds the rolling elements in place, keeps them evenly spaced and helps distribute grease equally within the bearing.

Why It Matters
The geometry of the cage design plays an important role in how it interacts with the rolling elements and needs to be carefully engineered to serve those functions without causing excess friction.

Test Lab Results
The competitor's design causes two points of contact with the rolling elements.

Twice the amount of surface contact when compared to NTN’s bearings’ single point of contact. This will increase friction which will add heat and rolling resistance to the bearing. These issues were created likely to compensate for the large variation in ball sizes (see above) as well as to simplify and speed up the assembly process, saving time and cost at the expense of performance and quality.