EVERYTHING YOU NEED TO KNOW ABOUT MOUNTAIN BIKE BEARINGS

Jun 29, 2023

Without the use and application of different types of bearings, your mountain bike would cease to work, or at least work smoothly. How bearings are used plays an essential role with any bike. Tucked away and often out of sight, bearings enable the spin of a shaft (spindle) or rotation around a shaft (axle) under load. Most owners do not take into account these purposes. Just think, without bearings, the rider could not steer, roll, pedal or have a properly working drivetrain. Bearings are found in the hubs, bottom bracket, headset, suspension pivots, pedals, shifters, pulleys, forks, shocks—the list for bikes goes on. Fundamentally, any non-stationary component on your bike tends to have some kind of bearing.

Loose-ball, caged-ball, bushing, needle and cartridge are the main types of bearings found in cycling frames and components. The least complex is the bushing style of bearing. A bushing (also known as a sleeve bearing to some) is typically used in shock mounts, some suspension pivots and the more affordable pulley wheels or shifters seen on the market. This system uses a sleeve that sits between two surfaces to reduce friction.

Caged and loose balls are the two classic types of bearings and usually come to mind for bicycles and will be found in a typical cup-and-cone assembly. The balls for this bearing run along the smooth, machined finish surface of the cup and cone that match their shape. Although to some this tech is "outdated," in many ways it still has advantages. Shimano still utilizes this bearing type in its hubs, claiming they offer greater strength than sealed-cartridge industrial bearings due to their ability to displace lateral and vertical loads more effectively. These bearings are angular contact (we’ll cover more on this shortly), have simple steps to maintain/service, and perform well when preload is adjusted properly.

Sealed—also known as cartridge—bearings are now the go-to choice and most commonly seen in bike components. Radial cartridge bearings are the most common, as they are cheaper, but they are only meant to carry the load in a truly circular movement. This would primarily be vertical loads if looking at the hubs, bottom bracket-crank connection, and suspension pivots or derailleur pulleys. Since there is no inside or outside direction of a radial cartridge bearing, they do sacrifice a bit of performance and are of less quality than an angular-contact bearing, but this does make them more affordable with some components. They are almost always pressed into a bearing bore.

A typical radial cartridge consists of an outer race, an inner race, ball bearings, a cage/retainer to hold bearings, and two seals to keep dirt out. The radial cartridge bearing cannot be fully disassembled. There are some sealed bearings with one seal, which are often seen with integrated headsets. Like all bearings, the cartridge style requires precision from the manufacturing side right up to the mechanic performing the installation. For example, poor manufacturing tolerances used by some bike brands in the past have given press-fit bottom bracket bearings a bad reputation for creaking. The fact is that a properly manufactured press-fit bearing interface is just as good as a thread-in style when properly executed. The downside to typical cartridge bearing designs is that they do not handle lateral loads as well as an angular-contact bearing. For that reason, you will sometimes see a row of multiple cartridge bearings to produce the same result.

"The most common mistake riders make is washing their bikes with pressure washers and directing that powerful blast at the bearings."

At the other end of the spectrum, angular-contact bearings require higher tolerances since they have an inside-outside directional component. Some brands have even built a reputation with their ability to apply angular-contact cartridges with their finely made products. Compared to a radial cartridge bearing, an angular-contact cartridge can take on loads from all directions, just like a cup-and-cone system in terms of design. Working with radial and side-force loads piled on with every rotation of components requires these extreme tolerances in mating surfaces to provide better rolling performance. Angular contact bearings are usually used in the hubs, cranks and suspension.

Not widely applied to bikes, but still utilized for specific needs, needle bearings are being seen more frequently because they can handle a far greater radial load than any type of ball bearing. Although they are typically more expensive to manufacture and require an exact interface, needle bearings deliver high performance with a sturdy design in certain applications. We will usually see needle bearings being used in pedals, some newer suspension designs (see page 58 for an example) and occasionally in some headsets. Overall, needle bearings can create smooth rolling under loads with a more even distribution of higher loads on the needles than round ball bearings.

The best bearing is one that is of good quality, rolls without a hiccup and lasts between service intervals. Each bearing has a quality level or grade—referred to as ABEC—followed by a number. The higher that number, the higher the grade of the bearing. Some feel this rating system is insufficient, as it neglects how loads are handled, the balls’ precision and the hardness of the material used (measured on a Rockwell scale).

What the ABEC standard can help identify is the bore diameter, the width and the variations in the groove in which the balls sit. As the co-founder of Enduro Bearing, Matt Harvey told the MBA wrecking crew, "The materials are far more important than the ABEC ratings." Even though that is the case, ABEC-3 and -5 are adequate for all things bicycle. To meet the ABEC-5 standard, the bearing design must pass all tests—noise testing at high rpm, extremely close tolerances for the inner and outer bearing diameters, the roundness of the balls, the trueness of the races, and the micro-surface finishes of balls/races. The 7 and 9 ratings are a bit excessive, with that level of accuracy being left for machines that witness rotations in the thousands or hundreds of thousands of revolutions per minute. As wild as it would be to move parts of your bike at those fast rates, it's not a speed we will ever see.

"You’ll know it's time to replace a bearing when excess play or slop develops, you hear or feel a noise, or you notice pitting and wear and unwanted movement while servicing."

Each bearing may require a certain grease depending on where and how it will be used. Enduro Bearings uses several special greases which are all formulated by combining a base oil with a thickening agent.

In most circumstances, the harder the material, the better, but their limit before this is hindering performance. Too hard of a material and the balls can become brittle, which is the same if it's too soft, so there is a fine line to stay balanced on for the best results. Along with how strong the material is, it is equally important to consider how resistant it will be to corrosion when being put through mountain bike terrain and environments. Bearings are made from a huge range of materials. Some examples include chromium steel, 440C stainless steel, XD-15 super-nitrogen stainless and silicon nitride (ceramic bearings).

The good news is that the bearings are one of the lowest maintenance items on your bicycle. As long as they are not abused, bearings will offer years of reliable service. Treat them poorly and you can destroy all of them in short order. The number-one killer of bearings is water contamination and the resulting corrosion. The most common mistake riders make is washing their bikes with pressure washers and directing that powerful blast at the bearings. Water is forced past the seals, and it ruins the bearing if it's not cleaned and greased right away. Water can also be introduced by simply riding in wet conditions, so your bearings will need more frequent greasing and likely need to be replaced if you ride in wet conditions often. The other bearing killer happens before they’re even used—incorrect installation. Bad alignment or using the wrong tools can end a bearing's life before it even starts. That's why replacement and even service are often best left up to a professional mechanic.

If you want to keep a bike's performance levels at their best, then the moving parts, like your bearings, will need service at some point. Loose bearings are relatively easy to clean. Old grease can be wiped out and cleaned. We often just replace cartridge bearings since that's easier to do, but they can be cleaned with a skilled touch. You’ll use a thin pick to peel the seal off, work your way around the outside of the seal and slowly lift it out, being mindful to avoid damaging it. You can then wash the old grease out with a degreaser and then dry your bearings. From there, reapply the desired lube. If racing is your goal and you do not mind the short service intervals, go with lightweight lubes for less rolling resistance. On your winter/wet weather build you might run a marine grease to protect areas from excessive corrosion. Next, reinstall the seal, and reassemble the parts in the reverse order of disassembly.

You’ll know it's time to replace a bearing when excess play or slop develops, you hear or feel a noise, or you notice pitting and wear and unwanted movement while servicing. Finding a replacement bearing is typically as easy as getting a bearing replacement kit from the frame or component manufacturer. Older parts can be trickier to hunt down a source.