Bike hub bearings

Just back from a week and change of riding in sunny San Diego. It was mint, the weather was great, available terrain and variety is unmatched, the scene there is huge, and the company was excellent. Between the Mexican food and the poké (and maybe a beer or two), I gained 3 pounds despite riding 419 miles over 25 hours, with 32000 feet of climbing. 

Bearings can seem complicated, but knowing just a few things makes them a lot simpler. They are definitely very important, as without properly working bearings your bike won't work very well at all. After a lot of thought and research into things, we’ve decided to offer and stock replacement bearings and bearing-related stuff, so some info on bearings in general that gives insight into why we’re carrying what we are is useful.

We will be carrying sizes relevant to popular hub usage, and in both LLU and LLB sealing types (more info on that below). They are chromium steel, and very high precision. 

The first thing to be aware of is that there’s generally no such thing as a “bike specific” bearing. Some bike parts use obscure and unusual bearings, while some bearings are uniquely specific to a part (Chris King bearings, for example), but the gigantic majority of parts you’ll ever own use standard bearings. You don’t have to get them from a bike-related source, they’re just commercially available bearings. Knowing that, let’s go from there.

Friction – On your entire bike, there are only maybe 10 watts of bearing friction if your bearings are okay and are working about as well as they’re supposed to. In our opinion, the only time a bearing is going to cause significant drag is when it’s malfunctioning, either from corrosion or excessive wear. Therefore, we’re concerned with having good bearings and keeping them in good shape, rather than chasing miniscule benefits which can go sideways if conditions and maintenance aren’t ideal.

Type – There are cup and cone bearings, which use loose balls between a cup and a cone which create the race, and there are cartridge (or sealed) bearings which is what we’ll discuss. Cartridge bearings are self-contained units that are easy to source, use, and replace. They are used in the overwhelming majority of hubs used today, and in almost all of the hubs we build (Shimano being the exception). Angular contact bearings are a subset of cartridge bearings, which are made to work in situations with lateral as well as radial loading. Only use angular contact bearings where the bearing's side load is adjustable (as in WI and Chris King hubs, press fit bottom brackets, etc), and not where the preload isn't adjustable. You can use regular cartridge bearings in preload adjustable systems, but you don't want to use an AC bearing without a preload mechanism. 

Size - There are three measurements that you need to know for any bearing: bore (or inside diameter), outer diameter, and width. These are straightforward, and they then relate to the size name. For example, 6901 bearings have a 12mm bore, a 24mm outer diameter, and are 6mm wide. Any bearing with those measurements is a 6901 bearing and vice versa.

Material – Lots of different materials are used to make bearings, primarily chromium steel, stainless steel, and ceramic. Each has benefits and weaknesses. Stainless is weaker and softer than chromium steel, but more corrosion resistant. Ceramic is hardest of all, but often suffers from early breakdown. Ceramic bearings also cost an arm and a leg. Mixed materials also appear, but they create issues of their own, for example hard ceramic balls used with softer steel races cause the balls to score and ruin the races. For general use in bikes, chromium steel bearings with appropriate sealing and lubricant work best and are what we recommend.

Precision – Bearings simply come in different precision levels, commonly referred to as ABEC-spec. The higher the ABEC number, the more precise the bearing is. Since bearings are designed for WAY more demanding treatment than they get in bikes, precision is important but not ultra critical. The hubs in a bike going 30 miles per hour are spinning at about .15% of their capacity rating. All the bearings we use are high-spec in the absolute, but for bike purposes they’re much higher precision than necessary. Other factors quickly become more important, and ABEC 3 is plenty precise for bike applications. 

Sealing – Except in weird circumstances where you are trying to remove every scintilla of friction and care nothing for longevity, bearings are sealed. There are several types of seals, which primarily go into two categories: contact seals, and non-contact seals. Contact seals have a positive connection to the inner and outer races, where non-contact seals have a positive connection at one race and sort of “float” against the other. Contact seals seal better, while non-contact seals have lower friction. Again, friction differences are small, but when we’re talking about bikes people always pay attention to the small differences. For our purposes, LLU is a full contact seal system, while LLB is non-contact.

Some hubs (White Industries is one) come with “2RS” seals, which literally means 2 Rubber Seals. The RS seals are able to be removed with a blade or pick so that you can clean and refill the bearings. In our experience, these might be better in theory than in practice, and we prefer LLB and LLU seals. These seal images are from the Enduro Bearings web site. 

Fill – Also called pack, fill refers to which lubricant you use, and how much of it you use. You can use a heavy grease, or you can use a light oil. Heavy grease resists contamination better and lasts longer, while light oil has lower friction and breaks down quickly. Unless you are doing something where the least friction is absolutely A1 critical, grease is your best choice. Fill is expressed in percentage, meaning what percent of the available space is filled with grease. This will vary from somewhere around 30% to 100%.  Less fill is less friction, more fill protects better.

Removal – Taking bearings out is easy. Properly, you use a bearing puller, which is just a thing that pokes into where the bearing is, then you expand it, and then you pull it or hit it and the bearing pops out with the puller. For hubs, you can use a small wooden dowel and gently tap them out with a mallet. It’s possible to damage the hub shell using that technique if you aren’t careful, but if you’re not a gorilla this works just fine.

Installation – Using a drift, which is a bearing-size specific guide, is important. The drift helps the bearing go into where it’s going straight and not cocked. Press a bearing in cockeyed and you’ve got an issue which is hopefully just limited to a screwed up bearing. For a press, if you are just working with hubs, an 8” long piece of 3/8” threaded rod, plus some nuts and washers, makes a great press. But a proper press can be cheap and worth having.

Rehabbing Bearings – You can try, but once a bearing has gotten any sort of crunchy, it’s done. The best you can do is flush it out with WD-40, dry it out, put some new grease in there, and hope for the best. And that’s if you have the 2RS seals or can manage to remove other kinds of seals. In an emergency when you don't have a replacement handy, this may be all you can do, so give it a go. Prevention is the best medicine, and prevention means using the right kind of seals for you application, and after riding in more extreme conditions, exposing the bearing and drying it out with a cloth or carefully spraying air at it. 

 So there you have it. Our bearings section is up and running with only a few parts we have stocked already in it. More to come.