Cartridge bearings are an integral part of the modern bicycle and can be found on nearly every component whose purpose includes some type of rotation or oscillation; in virtually any application from headsets to hubs, bottom brackets to suspension pivots. We often take for granted the stresses and harsh conditions bicycle bearings endure, rarely thinking about them until they make noise or develop play, typically after countless hours of abuse.
So, what are cartridge bearings?
In the bicycle industry, cartridge bearings refer to a bearing assembly that can be entirely removed and replaced into the component such as a hub or bottom bracket. Traditionally, each bearing assembly in a hub would consist of four separate components; a cup, a cone, a retainer and balls. Each of these components (with the balls being held by the retainer) would be assembled as individual parts and then adjusted with nuts and threaded axles on a hub or spindle assembly. Cartridge bearings replace this four component assembly with one complete unit that is sealed with rubber seals. A radial cartridge bearing consists of an inner and outer race, a retainer holding the balls and then two seals to keep the grease in and the elements out. There is no adjustment feature for these bearings as they are made with internal clearance or play. They are typically mounted by pressing them into a bore, such as both sides of a hub flange, and then a slip fit axle is run through with stops behind the inner race of each bearing. Nuts or top caps lock the bearings and axle into place. Again, there is some internal play when they are tightened down. When the bearings wear out or they get rough or contaminated, they can be removed entirely for servicing or replacement.
What is the ABEC scale?
The ABEC scale and ratings refers to a number of tests and tolerances for radial ball bearings including measuring their individual components, assembled components, and tests such as high speed noise testing. Basically, these ratings refer to roundness tolerance of the inner and outer races, trueness of the raceways, and radial and axial runout of the races. While the ABEC scale traditionally has been used to pick out the best bearings for high speed applications, this does not directly apply to bicycle bearings, which are considered a low speed application. But, the scale does give an idea of the general level of precision and quality of the bearing. There are some other features which are more important for bicycle application such as ball groove depth, ball complement (diameter and quantity of balls) surface finish of the raceways, type and quantity of grease, design of seals, etc..., which are not factored into the ABEC rating. Most high ABEC tolerances require the bearings be mounted into high tolerance, ground surfaces with highly accurate spindles and bores to take advantage of the precision level and trueness, which most bicycle components do not have, as they are machined parts. In general, an ABEC 5 bearing is much more precise and accurate than the part it is being installed into. Higher ABEC level rated bearings are higher precision and have tighter tolerances.
What do the numbers on a bearing mean? For instance, 6802RS.
The numbers on a bearing refer to the series, dimension, and then the type of bearing. For instance, 6802 2RS refers to a bearing which is 15x24x5mm with 2 rubber seals. "6800" is the series beginning with a 10 mm bore. The increments go 10 (6800), 12 (6801), 15 (6802), 17 (6803), 20 (6804) and then 5mm bore dimensions from there. A 6804 has a 20 mm bore, a 6805 has a 25 mm bore (5 x 5mm = 25mm), etc. The 6800 series is called Extra Thin Line Bearings and 6900 would be Thin Line Bearings (larger section, heavier duty bearing. A 6902 2RS would also have a 15 mm bore, but with a bigger ball, and has a 28 mm OD. Finally, 2 RS literally means: Two (2) Rubber Seals. You may also find bearings with a number like 61802. AT Enduro that is how they designate their ABEC-5 line of bearings but dimensionally the 6802 is the same as the 61802.
How water resistant are cartridge bearings? Will washing your bike with a hose force all the grease out?
It depends on the grease and the seals that are used. "2RS" means Two Rubber Seals, but there are many types. The usual 2RS seal is a single lip which runs dynamically on the outer part of the inner race, the outer lip is static, and fits into a groove of the outer race. Enduro makes an LLB or LLU type, which is a double lip seal that rides in a machined groove on the inner race. This, along with a water resistant or marine grease will make it much more difficult for the grease to wash out of the bearing even when pressure washing. That said, bearings ridden for long amounts of time in the rain or pressure washed again and again will eventually need to be serviced depending on how often this occurs. Water will creep into any sealed system given enough time in a wet environment. Using heavy degreasers and soaps will also cause the grease to break down quicker, so be careful about what you spray on your bearings.
Here are the 4 variations of seal design that Enduro offers, LLU being the most effective at keeping water out and contaminating the bearing:
Why does play develop when a bearing is worn out? Are the balls themselves worn down?
Most times, it is the bearing raceways that are worn out when play develops. While the balls can wear too, they are generally harder than the raceways and will wear the races out first. This is especially true for ceramic balls, which are seven times harder than the raceways. This can be avoided by maintaining a proper amount of grease in the bearing.
What are angular contact bearings? What are the advantages of this design?
Angular Contact cartridge bearings (A/C) more closely resemble the traditional cup and cone bearings referred to back in point #1. While they can be made as cartridge bearings, until recently they could not be removed and replaced as cartridge bearings because they would come apart into three pieces when removed. This made servicing difficult, and if installed backwards, potentially disastrous. Enduro's newly patented A/C bearings eliminate these problems with a unique design in which they can be removed and replaced as other cartridge bearings without coming apart. A/C bearings do require a preload system being either a threaded axle with no inner axle stops, or a spring or wave washer system with no inner axle stops. With an angular contact hub or axle system designed to use these bearings, they can be adjusted to remove wheel play. As play develops, they can be readjusted to remove it. While the same can be done with radial bearings, these will wear out prematurely as the ball is rolling on a thin part of the race. A/C bearings are designed internally to have the ball located at a 15º angle when preloaded. Because all of the balls are always loaded on the races, there is always even load distribution.This is not true on a radial bearing with internal clearance, where some of the balls are carrying all of the weight as the wheel spins. In this way, A/C bearings will last longer.
What are the benefits of ceramic bearings? It seems like when they first came out they garnered a lot of press, but now you don't hear as much about them. Any thoughts as to why this may be?
Ceramic Hybrid bearings (steel races with ceramic balls) are still very popular and are here to stay. When they were first discovered by the bicycle industry, there was a lot of press because they were new. Suddenly, many companies were offering ceramic hybrids, but like anything, there were some very good ones, and some very bad ones. There was also a lot of misguided press claiming they would last forever. While they can last as long as standard steel bearings, in general, good ones will last the same amount of time as an all steel bearing. However, recently Enduro introduced XD-15 nitrogen steel races, and these will last much longer than steel bearings with ceramic balls. This steel alloy holds up to the hardness and non yielding ceramic balls, even without lubrication and exposure to any kind of elements. The Enduro XD-15 bearings will run just as smoothly a year or two later as the day they were installed, even without service.
So what sets Enduro apart?
Enduro produce bearings that spans literally hundreds different sizes and over half a dozen ranges and is supplied as original equipment on some of the leading bicycle brands, and has been so for 20 years. They are not simply the leaders, but quite possibly the pioneers of cycling specific bearings. But Enduro don’t simply lead because they were the first, they lead because their approach is unique: they set themselves apart with their holistic approach to bearing design in that they specify each component that makes up the bearing with the specific application in mind. What this means is that through careful design, Enduro are able to get the most out of each bearing that they produce. Though this can get a little confusing, the “core” lines are as follows:
ABEC ratings (Annular Bearing Engineer’s Committee) are standards to which each bearing must pass many tests in order to meet the scheduled requirements including noise testing at high RPM, extremely tight tolerances for the internal diameter, outer diameter, roundness of ball, trueness of races, and surface finish for all of the above. Some aspects of ABEC ratings are important for bicycle bearings, but not all. In fact a high ABEC rated number for a bearing does not necessarily mean a high performance, long lasting bearing for your bicycle. For instance, you can have a high ABEC rated bearing that has race grooves only half as deep as ours because this feature is not covered by ABEC ratings. Since the grooves would be shallower, there is less surface for the ball to roll on, and easier to pass the noise test. (Less surface contact = lower noise). However, the shallow grooves of this bearing can yield less than half the support of our deeper groove design, and can be only half as strong; last half as long and become rough much sooner. Enduro's deep groove ABEC 3* and ABEC 5* bearings offer the deepest grooves possible in every size, and are more difficult to pass the test due to the improved architecture of our bearings.
Balls are rated by their Grade. A Grade 3 ball means that the ball is 3/1,000,000” tolerance of sphericity, and so is extremely round. In fact, the races of any bearing cannot come close to this level of precision in their trueness, but every component being closer to perfect helps decrease friction. Another feature of Grade 3 is surface finish which in this case is free of scratches or skufs, and to a <0.003 micron fine finish. The lower the Grade number, the better the ball. Enduro only uses very high grade balls, whether steel or ceramic. Only 10 years ago, Grade 25 would be considered a very high grade ball, used in the best hubs and bottom brackets made. Enduro starts with Grade 10 balls and then Grade 5 or Grade 3 at the top.
Ceramic / Silicon Nitride Balls (Si3N4 material)
Made from pure Silicon Nitride material (Si3N4) with extreme high density from uniform compaction (3.25 g/cm3), the micro-structural elements of this material is second to none. In other words, it is extremely dense. There are several materials used for ceramic balls and races and Enduro only use the best which is Silicon Nitride material. Other ceramic materials should not be considered because of their inferior characteristics. The high precision Grade 3 or 5, Si3N4 pure ceramic balls are 3 or 5/1,000,000” from exactly round in sphericity. 60% lighter weight, and 7 times harder than steel; friction is reduced to near zero. Resistance to heat is 8 times greater than that of steel, tougher and less brittle than other ceramic materials, while there is simply no comparison for corrosion resistance or magnetic problems with our Si3N4 balls.
A word about ball size:
Remember, increasing the Diameter of a sphere by 2 times, increases the surface area by 4 times and the volume by 8 times. Refer to the diagram below for a better visual comparing the ball size of Enduro bearings Bottom Bracket bearing to the 3 other competitors for the SAME sized bearing, 24 x 37 mm. The red dot on each ball indicates the surface contact area that changes dramatically with the larger balls Enduro uses. Further to this, it is easy to understand why Enduro have developed their Angular Contact (A/C) designs for several levels of our bearing line. Compared to radial bearing design, you not only can use larger balls, but since A/C bearings are Pre-Loaded, all of the balls are always making contact in the races evenly. In the radial bearing diagram below, you can see how in certain situations for a radial bearing, only half the balls are making contact. And not always in the correct radial axis, since there is internal clearance or play between the balls and races. For A/C bearings, they are always loaded 100% of the time in an opposed 15º direction, carrying the load evenly and smoothly with more contact area. What this means is no wheel “flop” when you change direction on your bike, no rubbing of disc brakes to slow you down, and bearings running smoothly 2 ½ times longer than radial bearings.
In most instances, Enduro uses 52100 High Carbon Chromium Alloy Races with heat treatment followed by cryogenic treatment. Starting with vacuum de-gassed chromium steel alloy, and hardened to Rockwell HRC 64, these super high precision races are cryogenically treated not once, but three times during the final super polishing phase as in Zero, CH or A/C bearings. Cryogenic treatement means taking the races down to minus 310º Farenheit (-190º C) to nomalize the crystalline structure of the material so that the races will resist the hardness of the ceramic balls and get the maximum wear potential. This critical treatment to the races is left out by many manufacturers, but not by Enduro. For the top ZERØ bearings, Enduro also additionally give them a Magnetite finish (black in color or Black Oxide) which is corrosion resistant and further stabilizes the bearing assembly. The races are again polished after this process to give the smoothest ball path.
Grease and Lubricants:
Enduro use several special greases which are in general all formulated by combining a base oil with a thickening agent. They lubricate rolling bearings by bleeding a small amount of oil out of the “reservoir” of the grease thickener and into the raceway. The oil provides the elastohydrodynamic lubricating film needed to reduce friction and wear. Greases can also serve as effective seals to protect bearings from contaminants and moisture. For greater loads, especially where vibration or shock loading is likely, such as pivots or headsets, special anti-wear additives can improve grease performance. Likewise, special thickeners and additive packages can augment a grease’s natural resistance to wash-out by water or salt-water spray. Thickeners can also be processed to reduce the noise-generating characteristics of a grease. For instance, Enduro use Kluber 7272 which specifically addresses the issues of the two very different materials in a ceramic hybrid bearing. This grease only runs better and smoother with time and is highly resistant to washing out. It is engineered to stick to the balls and continually be pulled back into the ball path where it is needed. Other greases can end up pushed out to the edge of the ball path, doing nothing. For Enduro's ABEC 3 bearings they use a similar high pressure grease, Mobil XHP 222 which is an excellent and clean rolling grease and also has excellent water displacement characteristics. For the MAX type bearings and some bottom bracket bearings, Enduro fill the bearings both sides either CRC Marine grade grease for ultimate salt water protection, or Almagard 3752 for ultimate high pressure characteristics. These high pressure greases will not get pushed out by the extreme loads of a suspension bearing pivot for example.