A Comprehensive Guide to MTB Bearings with Matt Harvey from Enduro Bearings

May 12, 2023

Between the hubs, headsets, and pivots there's a large number of ball bearings that make everything spin smoothly. Our editorial crew was recently chatting about the bearings in our mountain bikes, and we realized that there is a bevy of questions we didn't have answers to. Thinking that readers might be similarly inquisitive, we contacted Matt Harvey from Enduro Bearings to learn more about the spherical bits that spin inside.

We wanted to examine the makeup of a bearing, when riders should service them, and what are the dos and don'ts of bearing replacement.

Why do we use bearings on bikes in place of bushings? Are there other ways to smooth rotation?

When I started at Fisher Mountain bikes in the early 90's we were working on the RS-1, one of the first modern full suspension bikes and we used steel-backed Teflon bushings, called plain bearings. With an elastomer rebound shock, the movement would work on the beginning of rough sections, but then bounce and rebound out of sync with the terrain and start to work against you. Or simply compress and not release, becoming a rigid bike. A year later when I was at Bianchi developing a full suspension design, we finally had some better spring and air shocks which could dampen rebound, however, the steel bushings were slow to keep up with the movement of the rear end. When we remade the frame with "rolling elements," or ball bearings, the rear wheel could finally follow the terrain and not bounce around.

The static forces needed to move bushings or plain bearings are much greater than that of bearings with rolling elements, such as ball bearings. When you have many of them, 8 or 12 on modern linkage suspension bicycles, this static friction noticeably slows down the movement of the rear triangle, making it more difficult to keep up with undulating terrain. Another drawback is they need constant lubrication attention to stay quiet.

There are other bearings with rolling elements such as tapered roller bearings, needle bearings, spherical roller bearings, however, because of the scale and weight of bicycles, ball bearings usually make the most sense.

Are there places where bushings work better than bearings?

Some frames are designed with bushings where there is simply no room to use a bearing with rolling elements. Also, they are common in pedal designs for the same reason — very little space between the spindle and the pedal body. My experience has shown there is really no place you would rather have a bushing rather than a ball or needle bearing on a bicycle if it is possible. Friction is simply greater with plain bearings.

What makes one sealed cartridge bearing better than another?

There are many areas here, but the most important point is the quality of the steel you are using. Most bearings are made from 52100 chromium steel, but there are many foundries making different quality levels. You need to start with very clean homogenous steel for races and balls. There is also 440C stainless steel, which also needs to be good quality. There are other inferior stainless steels used by bearing makers. Enduro bearings also use XD-15 steel, which is by far the best material to use for a ball bearing because they almost cannot wear out.

Seal design and material is next on the list. "2RS" literally means "Two Rubber Seals" but tells you nothing of the type of seals. We use LLU or LLB type seals which are dual lip seals that dynamically seal in a matching groove. Most seals are made from Nitrile Buna Rubber, but we also use Silicone material on higher-end wheel bearings because of its slippery lower friction qualities.

On any given bearing size such as a "6806 2RS" the bearing dimensionally is 30x42x7mm, however, it could have up to four different ball bearing sizes and quantities inside. More importantly, maybe, the groove depth can vary greatly. These two specifications can greatly affect the performance of the bearing, namely load carrying qualities. Small balls and shallow grooves will lead to a quick failure in a bottom bracket bearing, compared to one with larger balls with deep grooves. The "axial" or multi-directional loads of a bottom bracket bearing need this greater support.

What's the difference between standard sealed-cartridge bearings, needle bearings, and others?

Sealed cartridge bearings are radial or angular contact ball bearings consisting of 2 machined and ground bearing races, precision level forged ball bearings, a ball separator or retainer, and two rubber seals. Needle bearings consist of either a machined/ground outer race or more commonly a punched or formed outer race and then needles with a ball separator. The inner race is usually a machined surface or hardened and ground bolt. Needle bearings also can have seals if specified.

How do you all determine what size ball bearings to use in a BB, headset, or frame pivot?

For Enduro, it is a matter of fitting the largest ball into the complete bearing as possible in every case. Since bicycle bearings are slow-moving, high load bearings in every case, the largest ball with the deepest groove possible will be the best solution. Many of these same-sized bearings used in bicycles are used in electric motors which will spin over 10,000 RPM at light load. In this case, shallow grooves with smaller balls can work well for low noise and accelerations. Seldom is any bearing in a bicycle surpassing even 200 RPM which is considered low speed. The forces of the bottom bracket or a rear hub are radial and thrust, actually axial or multi-directional. You need maximum ball contact and support from the races to not pinch or skid leading to premature wear or power loss while pedaling. In our custom testing of bicycle bearings, this proves out every time.

How do you determine the thickness of bearing races?

While considering the largest ball, there are limitations to the race thickness when heat treating and cryogenic treatment are involved. If the section becomes too thin, it can warp during heat treatment. We have some secrets for that, but about 1mm is about as thin as you want to go for wall thickness.

What are the races and bearings made of?

Most bearings are made from 52100 chromium steel, but there are many foundries making different quality levels. You need to start with very clean homogenous steel for races and balls. In some cases of cheaper bearings, chrome-moly material is used, but not recommended. 440C stainless steel is a common high-quality bearing material. There are other inferior stainless steels used by bearing makers. There is 440A and 440B stainless which are inferior for bearing usage, but also common. Enduro bearings also use XD-15 steel, which is by far the best material to use for a ball bearing because they almost cannot wear out. XD-15 is a "Super Stainless" Nitrogen Steel. Briefly, it is re-melted under pressure with Nitrogen introduced which creates a chemical reaction where the carbons in the steel are homogeneously and permanently separated. This creates extremely tough steel which can withstand the constant pressure of ceramic balls without degrading, actually burnishing and improving smoothness with use.

What are the different greases used in Enduro bearings and how do you choose those lubes?

We use basically three types of grease: Mobil XHP 222 for ABEC 3 and 5 bearings, Almagard 3752 for MAX and headset bearings, and then Kluber Isoflex for Ceramic and Stainless Steel bearings. Mobil XHP 222 is a good all-around grease that provides great protection and is resistant to water washout while still spinning fast. It is extremely stable in very hot or very cold conditions and is resistant to separation. Almagard is a super extra high-pressure grease meaning that it cannot be pushed out of the way even under the extreme pressure of a ball pressing down with maximum force. Almagard acts as a pillow between the balls and race where the bearings are not consistently turning, but fretting so that you do not get the associated wear. Kluber Isoflex is a very sophisticated and very "fast" grease that also can resist wet conditions and protect. Kluber has excellent sheering capabilities that you almost don't notice that it is grease but feels like a light oil.

How do the seals on cartridge bearings work?

Seals are press-fit into a matching groove that is machined into the outer race to retain them on both sides of the bearings. Most seals have a single lip that "rides" on the inner race (hopefully). Some do not make contact when you look closely, which is great for spinning, but lousy for protection. In the case of Enduro, we have another groove machined into the inner race so that the dynamic double seal makes contact on two edges of the inner groove for maximum protection against dirt while keeping the grease retained.

What's the best way to waterproof a bearing?

The dual lip groove type seals mentioned above provide better protection, but what happens next when you start turning the bearing is what really helps waterproof a bearing. Enduro fills both sides of every bearing with a 90% grease fill (most factories only fill one side at 35%). When the bearing goes into use and begins turning, some grease will begin to purge through the dynamic sealing lips, creating a trapped grease barrier between the seals inside the groove. This locked grease barrier continues to protect against water intrusion.

Is there a way to design bearings to take force from more than one direction? For example, the bearings in a trunnion shock mount mostly manage force in the direction of travel, but there can also be a large lateral load. Bottom bracket bearings would possibly be a better example since the force we put into them is rarely 100% linear.

Yes, we design our BB bearings with a 15º angular contact design with 4mm balls and very deep grooves. Since an angular contact bearing must be preloaded against another, all of the play is removed and it is guaranteed that all of the balls are engaged sharing the load all of the time. This is not always true in a radial bearing where some of the balls are under load while some float. When axial or multi-force loads are applied to our BB bearings, all of the forces are shared through contact angle by all of the balls. This makes for smoother rolling without skidding or pinching balls where you are losing energy or wearing the bearing out.

What's special about ceramic and ceramic-hybrid bearings? Do they really last longer and/or roll smoother?

When engineered and made correctly with the right materials, ceramic hybrid bearings can last longer and roll smoother. Full ceramic bearings cannot resist the impact or large forces for most component functions, so we do not offer them. On the other hand, XD-15 ceramic bearings will outlast any steel or other ceramic bearing on the market. For reasons mentioned above regarding the XD-15 material, they have a lifetime warranty, even against corrosion. In our other ceramic bearings, ABEC 5 and Zero, we further treat the chromium steel races with Black Oxide and Cryogenic stages which further normalize the steel, and not only do they last longer, they roll smoother longer. Ceramic balls are seven times harder than steel balls, so you have to account in the design of a ceramic hybrid bearing. A steel ball in comparison is "soft" and will flex or squish under pressure, whereas a ceramic ball could be compared to a piece of granite that will not yield. It is very difficult to measure the difference in rolling resistance of an all-steel ball-bearing compared to a ceramic hybrid, however, there is some current testing we are doing in our lab which shows positive results with XD-15 ceramic bearings.

You all make tools to deal with a lot of bike standards. How do you feel about the lack of consistency with things like bottom brackets and pivot bearings?

The bicycle industry is full of inventors and mavericks, so this is not new to our industry. With over 40 or 50 "standard" BB designs that we have to account for, and over 300 different pivot bearing sizes and specifications, it is a lot to keep up with. We began making tools many years ago now to help install and remove our bearings as people were using hammers and screwdrivers on bearings. We make the tools here in the USA, very high quality in our own facility. We never thought we would sell that many as they are expensive too, however, we are always challenged to keep up. It's just what we do; solve all of those problems.

Is it a good idea to pressure wash a full suspension bike? How will it affect the bearings?

It's not a good idea, but I’m lazy and do it all the time to mine. Of course, I’m always interested in the worst-case scenario, and it helps me think of a new way to solve problems. We now have "MAX Shields" stainless steel metal mechanical cover seals that resist pressure washing of MAX-type bearings. We also have Solid Lubricant MAX bearings which is a solid "grease" inside the bearing that resists this treatment as well. I think you have to count on people pressure washing, so it's up to us to find the best answers.

How are the tolerances on mountain bike frame bearing seats? Does Enduro have to do anything to accommodate frame tolerances?

It can vary from manufacturer to manufacturer, sometimes greatly. We have C3 and CN bearings generally available. This refers to the play or internal tolerance of the bearing. CN is tighter than C3 fit. If the press interference fit is tight, then a C3 bearing helps. You don't want the bearing too tight where it feels like it is indexing or rough, it will wear out very quickly in this case. If there is extra play, usually this is not a problem unless it is something like a front wheel that you immediately notice. Then you probably need some CN-fit bearings.

Some bikes have issues with the pivot inserts breaking loose, causing creaking and baggy linkage. Have any frame manufacturers worked with you to resolve this issue? How often do bike brands contact you to resolve issues or develop new products?

This one I have never been contacted about solving, though we get contacted frequently to solve similar problems. Sometimes we get drawings, sometimes samples. If the bearing seat has bowed out on a linkage and the bearing no longer has a press-fit, I would recommend Loctite 638 retaining compound, it can cover even large gaps. Based on bearing life alone, what full suspension bike would you recommend for someone who rides regularly in a wet climate?

There are so many good ones now, that is difficult to say. Of course, I have my biases, but we supply more than 70 brands so I remain neutral! Really though, almost all of the full suspension bikes are so good now.

Can you share some common mistakes you see with bearing removal and installation?

In fragile linkages, as you mention above, it is easy to damage them if you are not using a descent blind puller tool like ours or something similar. Pressing against the linkage with a leverage tool can often mark or damage the linkage. It is especially true if they are using a seating compound to hold the bearings in. A blind puller is the only way to guarantee no marks, no damage to your expensive linkage part.

What are some tips for proper bearing removal and installation?

A few things people don't remember: Remove those snap rings first! Sometimes they are hard to see but check the manual first before mangling the part trying to get the bearing out. Use Loctite or bearing compound releases best with a sharp "whack" rather than a gradual pull. Again the blind puller with slide hammer works best. Use the freezer when you are installing spindles through bearings or installing bearings. It not only holds your beer, but it makes putting parts in a lot easier if you remember it.

Apart from a crunchy and/or dry feel, how can readers know if their bearings need to be replaced?

Crunchy or dry feel often means you just need to clean the bearing out and put some grease in. Remove the seals, degrease and clean out the bearings and dry them out. Once clean and dry, put new grease in and replace the seals. You may still feel a little dirt in there, but they may be fine and smooth again. A good test to see if your bearing just has dirt or has galling is slowly turn the bearing in your hand. If the rough spots move around, it's dirt. If it is the same spot over and over again, it is a pit in the bearing.

Can all bearings be cleaned and repacked, or are there some that simply have to be replaced once they’re spent?

Oh yes, we do it all the time for people and send them back. You need to eventually service your bearings if there is no more grease and just dirt inside. The one exception is XD-15 bearings, you don't need to do any servicing if you don't want to.

What are some key differences between bike bearings and those used in motorcycles and other applications?

Motorcycle bearings and almost every other machine like a forklift are over-engineered because weight is not a factor. A forklift has bearings in it that will take 10 or 20x the load force they will ever see. They don't care about the weight. Nor is it a huge factor in a motorcycle, it has a much larger engine than the human one. So in bicycles, we are always using bearing sizes that are right on the edge of not working, because we are trying to make a 12-pound bike.