Bearing Basics

The word “bearing” at its most simple definition is a machine element that allows one part to bear the weight or load of another. Bringing this definition more into focus with regard to bicycle use, a bearing constrains relative motion to motion in only a desired plane or direction, and at the same time reduces friction between moving parts. The loads that a bearing can be expected to bear are defined as follows:

Radial Load is force applied directly on top of the outer bearing race, perpendicular to the shaft the inner bearing race is spinning on.

Axial or Thrust Loads are similar and describe force applied to the side of a bearing, parallel to the shaft the inner bearing race is spinning on.

Combined Loads are multi-directional forces, both radial and axial, applied simultaneously to the bearing and shaft the inner bearing race is spinning on.  Combined load testing best replicates real world bicycle use. Placing a 30 kilo weight beyond the crank spindle where pedal forces reside for one million cycles is an example of bottom bracket bearing axial load testing.

 We can further define bearings in five distinct groups:

Plain Bearings do not include rolling parts and are often referred to as bushings. They offer a very low manufacturing cost and best suited for low impact, minimal load applications where optimizing performance is a low priority, or where lubrication is plentiful and ingress of contaminants is close to nonexistent. Enduro doesn’t manufacture plain bearings. In fact, our first MAX bearings were designed to overcome problems associated with troublesome plain bearings in early full-suspension designs.

Cylindrical Rollers – in cycling applications, these are most commonly known as needle bearings. Roller bearings are ideally suited for high radial loads in applications where there isn’t enough clearance for a ball bearing, such as pedals and shock mounts. To work properly the mating parts must be very accurately machined, and these bearings should be paired with thrust bearings, washers or ball bearings to remove side-to-side play. Product engineers often combine roller bearings with radial bearings along the pedal spindle to optimize performance and durability. Enduro manufactures roller bearings used in pedals, shock mounts and suspension pivots.

 

Thrust Bearings are designed to function on a perpendicular axis compared to the more prevalently known radial bearing. Thrust bearing design sandwiches balls between two platform races; the bearing beneath dad’s favorite velour La-Z-Boy rocker is a thrust bearing. Another great example of thrust bearing use is the turret on a crane, where the tread wheels are anchored in one place while the manned crane can spin a full 360º. 

Radial Bearings are the ball bearings most people see in their mind’s eye when they think of bearings. These are the most prevalent bearing that you are likely to find in any part of a bicycle. In most cases, the balls are nestled in a retainer ring to maintain spacing and promote friction free spinning, and the bearings and retainer are sandwiched between precision machined inner and outer races. In Enduro Innovations, we share how Enduro’s MAX full-complement line-up has optimized radial bearing design for suspension pivots and pedals by eliminating retainers and increasing the number of bearings within the races to better absorb frequent impacts or load spikes.

Angular Contact (AC) Bearings are a “cup and cone” assembly, where the two races sandwich the balls at a prescribed angle. This allows them to manage radial, axial and combined loads. AC bearings are ideally suited for preloaded applications such as bottom brackets and headsets. Because they can be preloaded, AC bearings allow for precise sideload adjustment, eliminating free-play or “slop” while still smoothly handling radial load. Whereas radial bearings at times only provide 50% ball-to-race contact, AC bearings promote 100% contact, with the balls held in very light tension between opposing angular bearing races. To double down on durability, Enduro AC bearings include larger balls that smoothly carry greater loads while eliminating headset rattle or the micro-slop in wheel hubs that can contribute to disc brake rub. Enduro AC bearings are used in headsets, bottom brackets, hubs and suspension pivots.

The myriad combinations of Bearing Identification Numbers that can be found on bearings are a very specific and ordered code. This is the shorthand of bearing description. For instance, 6902 identifies a “Thin Line Series” bearing. The “6” indicates it’s a radial bearing. The “9” refers to thin line series. The “02” specifies a 15mm bore. 

6803 is an “Ultra-Thin Line Series” radial bearing. As with 6902, the “6” refers to a radial bearing. The “8” refers to ultra-thin line series. The “03” refers to 20mm bore.

In cycling, there are many odd sized bearings that reside outside bearing industry identification standards. To accommodate each of our custom bearing solutions, Enduro Bearings created an alphanumeric identification system many years ago that other companies now use. For example: “MR 18307 LLB” refers to a metric radial bearing, sized 18x30x7mm with LLB seals. And ”DRF 152610 LLB” refers to a double-row, flanged radial bearing, sized 15x26x10mm with LLB seals. We’ll get into seals further downstream, bear with us here!

ABEC Ratings (Annular Bearing Engineer’s Committee) are manufacturing and testing standards that each bearing must pass. These include noise testing at high RPM, precisely defined tolerances for inside and outside bearing diameters, roundness of ball, trueness of races, and the surface finish for all of the above. ABEC ratings are numbered 1 thru 9, odd numbers only, with 9 being the best possible rating. A bearing with a 7 or 9 rating is very difficult and expensive to manufacture, might be perfect for a 40,000 rpm dental handpiece, but is overkill for the slow rotational speeds of bicycle cranks and wheels.

Some aspects of ABEC ratings are important for bicycle bearings, but not all. In fact, a high ABEC rating does not mean the bearing spins with less drag, nor does it necessarily equate to high performance, long lasting bearings.  ABEC standards do not account for critical bicycle performance influencers such as load handling capabilities, ball grade and precision, Rockwell hardness, bearing seal quality or lubrication specification. This can lead to confusion in the bicycle marketplace.

For instance, a high-ABEC rated bearing that includes a very shallow race groove will run very quietly, but will also be more susceptible to the axial loads typical to cycling and as a result may be subject to premature wear and potential failure. Conversely, Enduro’s ABEC 3 and ABEC 5 bearings – designed specifically for bicycle application – offer the deepest grooves and largest balls possible in every size to increase bearing strength and durability. Due to this increased ball size and groove depth, our bearings require tighter manufacturing tolerances combined with exacting finish and assembly protocols to meet ABEC standards, resulting in greater precision overall.

Bicycle Bearings generally include inner and outer bearing races, balls or rollers, inner and outer seals and lubricant (grease). To determine the best bearing solution for each application, Enduro’s R&D group judiciously studies each use case, machines a large batch of pre-production samples and engages in extensive lab and field testing. 

Let’s start with Bearing Balls. Enduro Bearings’ design philosophy is simple: bigger, rounder, smoother, and manufactured from the highest quality materials we can find. This ensures a bearing that will roll better and last longer. A ball that is twice the diameter has eight times the volume of its half-sized counterpart, and will absorb much more punishment. Enduro bearing balls are far less likely to pinch, skid, jam, ovalize, chip, or explode.  We’ve included a BB30 bottom bracket illustration showing the size difference of Enduro Bearings balls compared to two of our respected, widely known competitors.

Balls are rated by grade. The lower the number, the more precise the sphericity. Only 10 years ago, Grade 25 was considered a very high-grade ball, and used in the best hubs and bottom brackets. Starting with clean steel is a must for precise, long-lasting spheres. Our Grade 10 and Grade 5 balls are forged and ground from 52100 chromium steel. Surface roughness is also a consideration. It can affect sphericity to a degree but is not specifically included in a ball’s grade rating. However, a smoother ball can enable a better ABEC rating and will also ensure a longer lasting bearing.

Silicon Nitride Ceramic Balls are made from pure Si3N4; an extremely dense and uniform material. The micro-structural elements of this material are second to none. Enduro only uses Japan-sourced (Toshiba or Panasonic), high precision Grade 5 ceramic balls that are 60% lighter and 7-times harder than steel, and are ground to near-spherical perfection - within 5/1,000,000” of round. Si3N4’s heat resistance is 8-times greater than steel; it’s tougher, less brittle and there is simply no comparison when it comes to corrosion resistance, nor is there any possibility of magnetic interference, due to the non-ferrous nature of the material. When paired with Enduro’s exclusive XD15 Nitrogen Steel bearing races, friction is greatly reduced and at the same time this bearing represents the absolute pinnacle of toughness and performance in adverse conditions. All XD15 ceramic-hybrid bearings include a lifetime guarantee.

440C Stainless Steel Balls are not quite as bulletproof but also nowhere near as expensive as ceramic balls. Enduro’s 440C stainless steel balls, thanks to the exceptional corrosion resistance characteristics of stainless steel, are an excellent choice for wet weather climates where standard steel bearings seemingly rust overnight. 440C provides high-level hardness, toughness and dimensional stability, and is extremely resistant to rolling-contact fatigue and corrosion. Additionally, stainless steel is more shock absorbent than many other steels, making it an ideal candidate for headset applications. Our MAXhit line is made entirely of 440C Stainless Steel, including races, and each MAXhit component comes with a lifetime guarantee.

52100 Chromium Steel Balls riding inside deep-grooved bearing races are what's inside Enduro’s ABEC 3 (grade 5) and ABEC 5 (grade 10) bearing assemblies. 52100 chromium steel balls riding inside deep-grooved bearing races. 52100 chromium steel can be manufactured to very high levels of precision, and when combined with double lip seals and filled with high performance grease, is the basis of an excellent bearing. Bearings made from 52100 chromium steel are found on many of the highest priced bikes from the most respected brands in the world. They offer premium performance and dependability at a very affordable price.

Bearing Races are what sandwich the balls inside a bearing assembly. Every bit as important as ball selection, race material and design is crucial. Enduro’s line-up includes three different bearing race materials, each with unique performance attributes. We also specify a handful of post-machining treatments to enhance bearing performance and longevity.

XD15 Nitrogen Steel Bearing Races are an Enduro exclusive. Our ceramic bearing line utilizes XD15 advanced stainless alloy races which provide unequaled corrosion resistance and strength. Interestingly, XD15 nitrogen steel was developed for use in airplane wings in order to withstand the caustic chemicals used during de-icing. This very special nitrogen infused steel material will absolutely not rust or corrode. Even riding on the beach in salt water or drowning a bottom bracket bearing in sugary nutrition drinks will not affect the material’s integrity. Dirt and sand will not pock mark or accelerate aging; these contaminants simply polish the races smoother.

The XD15 manufacturing process involves re-melting a very high grade of martensitic stainless steel in a highly-controlled chamber while introducing nitrogen gas to produce a homogenous steel, free from coarse carbides, resulting in ultimate fatigue resistance. The resultant steel alloy is too tough to draw into tubes, so XD15 bearing races must be machined from rod stock.

Enduro XD-15 ceramic-hybrid bearings combine corrosion-proof, cryogenically treated nitrogen steel races with Silicon Nitride Grade 5 ceramic balls to create the ultimate high performance bearings and components. When compared to other ceramic bearings on the market that claim speed and power advantages on day one, Enduro XD-15 bearings not only provide these same performance advantages, they actually get faster and smoother with use and can be depended upon to perform in the harshest environments. All XD15 bearings include a lifetime warranty.

440 Stainless Steel is available in three grades: A, B and C. Enduro uses only the highest grade: 440C. To improve bearing life and performance, the material is normalized and stabilized via multiple inert gas and cryogenic treatments. Like our 440C bearing balls, these bearing races offer the highest level hardness, toughness, dimensional stability of any of the most common martinistic stainless alloys, and are highly resistant to rolling-contact fatigue and corrosion. 440c is not as hard as 52100 but is much more corrosion resistant. It’s not as tough as XD15, but doesn’t cost nearly as much, and can still be an excellent choice where corrosion or high impacts are factors. Enduro’s patent-pending MAXhit 100% 440C Stainless Steel components are an excellent choice for wet weather climates and the hard hits experienced during mountain biking and gravel riding, and they come with a lifetime guarantee.

52100 High Carbon Chromium Steel Alloy races are featured in our most affordable and most popular bearing assembles. The manufacturing process for these high precision parts begins with a vacuum de-gassed chromium steel alloy that is hardened to Rockwell HRC 64 through heat and cryogenic treatment. Cryogenic treatment chills the material to minus 310º Fahrenheit (-190º C) to normalize the steel’s crystalline structure and promote longer bearing life, especially important when marrying these races with super dense, hard ceramic balls. Often ignored by other bearing manufacturers, cryogenic treatment improves bearing performance and longevity. For an additional layer of protection, look for Black Oxide treatment in our product catalog. Black Oxide is a Magnetite finish (black in color) that enhances corrosion resistance and further stabilizes the steel alloy. This treatment is applied three times. Black Oxide races enjoy an additional pre-assembly polishing to ensure a silky smooth ball path.

Seals are a bearing’s first line of defense against the elements. A well-designed seal keeps grunge out and lubricant in. Most bearing companies use “2RS” single lip seals. 2RS literally means “2 Rubber Seals”. Enduro Bearings manufactures special seals designated “LLB” and “LLU” for most bearing assemblies. These designations indicate a mating groove on the inner race where two sealing lips make light contact (LLB) or medium contact (LLU). Enduro’s labyrinth design fills the double-lip gap with grease as the bearing turns, creating an additional hydromatic seal. This added grease barrier dramatically improves bearing performance over time and extends bearing life.

Enduro’s bearing seals are made in our Taiwan facility to exacting tolerances and formed with a more pliable NBR (nitrile butadiene rubber – a strong and flexible rubber that lends itself well to bearing seals) compound to control surface irregularities. Enduro’s premium XD15 ceramic-hybrid bearings utilize silicone seals to provide exceptional sealing with reduced drag.

LLB Seals are Enduro's most popular light contact seal. LLB seals are comprised of Nitrile material rubber with a steel insert and ideally suited for constantly spinning bottom bracket and hub bearings. Rather than one thick 2RS seal lip rubbing on a blunt surface, LLB type utilizes two razor thin sealing lips riding in the bearing race groove. The outer lip keeps the water and contaminants out, while the inner lip retains grease for smooth function and longer intervals between servicing. 

LLU Seals are full contact, dual lip seals that slot into a groove on the inner race. With more sealing pressure than LLB seals, LLU seals are ideal for suspension pivots and headsets that only rotate a few degrees rather than continually spinning. The increased seal pressure helps retain the 90% grease fill to continually lubricate the balls and races, while keeping dirt and moisture out.

Enduro’s range of greases are formulated to include a base oil with a thickening agent. To lubricate rolling bearings, our specialty greases bleed a small amount of oil from the grease thickener and into the bearing raceway. The oil provides an elasto-hydrodynamic lubricating film to reduce friction and wear. Greases can also serve as an effective second defense inside our seals to protect bearings from contaminants and moisture. For greater loads, such as pivots and headsets, special anti-wear additives can improve grease performance. Likewise, thickeners and additives can augment a grease’s natural resistance to displacement by water or salt-water spray. This is where a grease is characterized as a “high pressure grease.” All the greases Enduro selects for all our bearings are high pressure greases.

Every Enduro bearing is filled with one of three lubricant types to optimize bearing performance and durability. Here are descriptions for our most popular greases.

Enduro Performance is our all-rounder grease. 'Performance', our branded Mobil XHP 222 (Extra High Pressure), is well-suited for all bikes and riding conditions. It’s an excellent, clean rolling grease that is not easily displaced by power washing or the elements. Balls will not push this grease to the side, leaving an undesirable dry contact point. ABEC 5 angular contact, ABEC 5 radial bearings ABEC 3 bearings are packed with Enduro Performance grease.

Enduro MAX Grease is designed to perform exceedingly well under high pressure. 'MAX', our branded Almagard 3752 grease, is perfect for suspension pivot and headset bearings that rotate just a few degrees. This thick ‘extra high pressure’ grease is used by Caterpillar and heavy equipment manufacturers for its superior tenacity and shock absorbing attributes.

Enduro XD15 Speed Grease is for fast moving bottom brackets and wheels. 'Speed' is our branded Klüber Isoflex “Fast” grease. XD15 Speed grease is not fragile; it features a unique formulation that sticks inside the bearing, providing long-term protection from the elements. Engineered to stick to the balls and continually be pulled back into the ball path, XD15 Speed grease is ideally suited for ceramic and stainless steel bottom brackets, hub bearings and jockey wheels. This  grease runs better and smoother over time and is highly resistant to washout. 

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