Bicycle Bearings: Bearing Size Guide
Have you noticed a rattle or play/backlash in the frame/suspension linkage of your bike?
You can check for play/backlash by gently pulling and pushing components, such as your wheels, to see if they move in directions that they shouldn't.
If you have checked your bike and have found you have excess play then no need to panic! It doesn't have to be an expensive fix, it might seem frightening but it can be an easy problem to solve.
Here is a quick guide...
Ordering the Correct Parts
There are many mountain bike bearing kits available at reasonable prices which also include sleeves and bolts such as this example.
Always make sure the parts are compatible, contact the supplier if necessary.
Money Saving Tips
Most bearings are fairly standard sizes and hardware companies such as RS Components or ACCU supply bearings that are up there with the best mtb bearings.
Finding the correct bearing is not so hard, all bearings should have standard part markings on them, see below diagram and image for guidance.
It's good practice to replace the sleeves and bolts but most of the time it is unnecessary.
By buying the bearings separately you can save yourself some shred tokens which can be redeployed on shiny bike parts!
Bearing Part Numbers
Bearing cartridge part numbers can usually be found on the rubber seal.
If your manufacturers manual doesn't tell you what size bearing you need then you can find out simply by removing the suspect components and noting down the bearing cartridge part numbers.
This part marking will be the same for the likes of your wheel bearings, free hub bearings, frame bearings and for the headset bearings.
Bicycle bottom bracket bearing cartridges normally come as an assembly. For the press fit type the assemblies have special flanges to allow the bearings to sit properly within the frame and seal internally, see below.
Some bicycle crank bearings are within a threaded body so that they can be screwed into the frame.
For some bottom bracket assemblies it is possible to replace the bearings in the same way in which you would replace a bicycle wheel bearing cartridge, however if you have a press fit bottom bracket like the one above you will have to replace the whole assembly.
For more info on what the part numbers mean, see the diagram below!
Radial bearings are the common bearing type used in pushbikes, you can also get roller type radial bearings but this diagram is of a ball bearing type.
As can be seen in this diagram the load is transferred through the outer race, through the ball bearings and then into the inner race.
Taper bearings are similar to radial bearings however they're designed to take some axial load as well as radial load. The below diagram is of a roller taper bearing.
Taper bearings are used for the headset bearings, however these are normally taper ball bearings.
Thrust bearings are designed to take all of the load in the axial direction, normally these bearings are used in applications such as clutch assemblies in engines.
6000 Series Bearing Size Chart
The above part numbers relate to the dimensions in the table below for quick reference.
Like with most things bearing dimensions were standardised long ago, the applicable standards are as follows:
Unfortunately ISO's business model is more manufacturer focused and you can't view these standards without paying and but luckily manufacturers provide useful information on their websites, such as Micro Blue Bearings or SKF.
Measuring the Bearings
Alternatively you can measure the bearing cartridges using some vernier callipers. With a bit of faff you can do this without removing the bearing.
There are three dimensions you need, ID (Inner Diameter), OD (Outer Diameter) and the Race Width.
See the diagram to the right for further guidance.
Once you have the dimensions you can simply search on google, or one of the previously mentioner hardware websites, and you should be able to find the bearings you need in no time.
Bearings fall into the category of 'wear parts' along side tyres and brake pads. Under the correct conditions bearings can last a very long time, but unfortunately conditions are seldom perfect when it comes to push bike applications.
The main causes of wear:
Shaft & bearing misalignment.
Overloading/Loading in undesired directions.
Damage when installing.
How to prolong bearing life:
Correct installation - Use a bearing puller where possible, hammering can damage the bearing race.
Grease on installation - This will help lubricate the bearing and protect the bearing from water and dust particulates.
Avoid pressure washing bearings.
Avoid overloading - Example remove crank with a puller instead of tapping out with a mallet to save the bottom bracket bearings.
Reference , .
How to Replace Bearings
Most bearings are interference fit and so if you operating on a budget you should be able to do most jobs with a socket set, copper and hide hammer and punches. However, fancy tools are available! See our article on How to Press Fit a Bearing.
Here are some quick tips:
If you're having to use excess force often there is something wrong, check there are no clashes and that everything is going in square.
Always prepare the mating surfaces and ensure they're free of debris and obstructions.
Often using a small amount of grease aids installation.
Some bottom bracket bearings are screw fit.
If you're finding a bearing to be a particularly tight fit on the OD them chuck it in the freezer. The bearing will contract as it gets colder and therefore the OD will shrink slightly.
If cooling the bearing doesn't work then try cooling the bearing again and gently heat the receptacle for the bearing with a heat gun but be careful not to damage any paintwork. Heating the receptacle will cause the material to expand and therefore should reduce the level of interference between the receptacle and the bearing.
 - Upadhyay, R., Kumaraswamidhas, L. and Azam, M., 2013. Rolling element bearing failure analysis: A case study.Case Studies in Engineering Failure Analysis, [online] 1(1), pp.15-17. Available at: <https://www.sciencedirect.com/science/article/pii/S2213290212000065>.
 - Aditya, Amarnath, M. and Kankar, P., 2014. Failure Analysis of a Grease-Lubricated Cylindrical Roller Bearing.Procedia Technology, [online] 14, pp.59-66. Available at: <https://www.sciencedirect.com/science/article/pii/S2212017314000450>.