Bicycle Bearing Purchasing Guide

Bearings are to a bicycle what peanut butter is to a P&J sandwich—without them, your bike just feels incomplete. In this installment, we’ll cover the most important parts about bicycle bearings, which is knowing what bearings you need, how to measure them, and common problems to avoid. Considering that this article will focus on theory over practice, I ask you to read it patiently~
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Before we officially start the content, we need to remind everyone that much of the knowledge covered here involves the field of professional mechanics. If you know nothing about front derailleur adjustment and wheel axle correction, it is recommended that you consider looking for a professional to replace the bearings. Regardless, we hope you find this in-depth and professional article as interesting as possible.

First focus on cartridge rolling bearings

Cartridge rolling bearings (also known as sealed bearings or deep groove ball bearings) have become the most common bearing type on modern bicycles and are designed to meet the needs of enthusiasts or high-performance use. These bearings are designed as a self-contained unit consisting of an inner ring, an outer ring, rolling elements and, in most cases, ball retainers and seals.

This article only focuses on cartridge rolling bearings. But other bearing types are also common on bicycles. Many bicycles sold on the market today still use loose ball bearings, nylon sleeve bearings or other similar cartridge rolling bearing alternatives in the traditional bowl + gear structure. These alternatives are generally easier to repair, but may come with their own complications. As a beginner, ParkTool has a lot of knowledge about other types of bearings besides non-cartridge rolling bearings, such as hub loose ball bearings.

Okay, back to the cartridge rolling bearings. There are currently no standards for mandatory bearing sizes or types for bicycle components. We often see multiple different bearing sizes within a single rear hub, or full suspension mountain bike linkages using different sized bearings at each pivot position. Also, there’s a big sinkhole, which is that occasionally you’ll find custom-sized bearings that may be twice as wide, have a different bore diameter, or an extended inner ring. There is no doubt that if you want to explain customized bearings clearly, you will have to open another pit.

Even more outrageous, in some cases the bearing codes printed on the surface do not correlate with the actual dimensions, or, more often, the codes are no longer legible due to corrosion and wear. And this is where we hope this article can really shine.

It is not uncommon to remove bearings like this from bicycles

It is not uncommon to remove bearings like this from bicycles

How to read and see through the bearing number

In case you don’t know, I need to remind you that there is actually everything on the Internet. More than ever, manufacturers are uploading dealer manuals, product diagrams, or product schematics so you can find the product number you need for repairs. In the best case, the manufacturer not only provides you with the manufacturer’s own part numbers for other standard bearings, but also provides the bearing size or bearing type you require.

However, sometimes manufacturers decide to only provide this information to their dealer network (hate brands like this, DIY players have no rights), or may simply base product definitions on components where bearings cannot be maintained (common in freehubs, pedals and some bowl sets). In these cases, mechanics will typically disassemble the assembly to determine the specific model of bearing that needs to be replaced.

In my experience, looking for answers about bearing sizes on forum posts or YouTube can be time consuming and the results are indistinguishable. So, I usually go straight to the source. My standard approach is to search a search engine for “make x model x diagram” (or “dealer manual” or “exploded diagram”). To increase efficiency, you can also add “.pdf” to your search engine to prioritize results for official PDF documents; often these files are from brands, or other times you may find leaked versions that are only for resellers. . Here’s an example.

A page from the 2023 Turbo Levo manual that provides all the necessary information related to the required bearings

Pictured is a page from the 2023 Turbo Levo manual which provides all the necessary information related to the required bearings

Some brands do a great job with this type of manuals and information, brands like Specialized, Ibis, Orbea, Hope, Wolf Tooth, etc. are super transparent with this type of information. Also, brands like Trek and Canyon will usually tell you the specific product numbers of their bearings, and then entering these numbers on their respective websites will give you the exact dimensions to copy – it’s an extra step, but if you It’s actually not too much trouble if you know where to look.

If you are reading such product brochures, please be aware of brands whose nominal bearing sizes differ from adjacent integers by hundredths or even thousandths. For example, if a hub’s manual states that it requires a bearing with an outer diameter of 16.99mm, then they are probably trying to sell you their own bearing, which is actually the same thing as a bearing with an outer diameter of 17mm.

Typically, machinists still need to disassemble the corresponding parts in order to read the bearing code that is molded into the rubber bearing seal or laser-etched into the side of the bearing (commonly found on headset bearings).

Although sufficient lighting or a flashlight can help you see these codes, reading these small bearing codes is a test of eyesight in most cases. A helpful tip is to take a photo of the bearing code with your smartphone in good light. Today’s smartphone cameras are great at macro photography, capturing numbers that your eyes can’t easily capture.

Your smartphone can be a handy tool for reading bearing codes

Your smartphone can be a handy tool for reading bearing codes

Reading bearing codes or looking for such codes in the part manufacturer’s documentation is often the safest option, but there are still some risks. For example, “6903 or 61903 bearings are a common size, however some front hubs have bearings with an 18mm bore diameter (i.e. 18307 bearings), while 6903 should be 17mm,” says Duncan Miller of DIY-MTB, an Australian specialist bicycle bearing sales company. Put it this way.

If you’re not sure, it’s time to take some measurements yourself. Sometimes you can do this with the bearing pressed into the seat, but usually disassembling the bearing first and then measuring it will avoid ordering the wrong product.

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