Bicycle Hub Bearings
by John Neugent
John Neugent probably knows more about bicycle wheels than anyone else alive. Maybe more about bikes as well. He's spent his life in the bike business, at every level. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price. If you are in the market for a set of wheels, please, check out John's site. He really knows his stuff. —Chairman Bill
In the old days when I started in the bike business, most hubs used loose ball bearings with forged cups and cones. The high quality hubs (Campy) machined the races in the cups and on the cones to make them smoother.
Then, sometime in the early 70s a few US made hubs introduced cartridge bearings in bicycle hubs. The small hub makers didn’t have the money for making cups and cones, but just as importantly had figured out cartridge bearings offered a better solution.
The bike industry is small. Most people think it’s big but compared to other industries it’s not (about $6B in retail sales in the US). Not only is it small, it’s highly segmented so that the high end business is really small. Because development costs are amortized over a small number of production units, final costs tend to be high.
The electric motor business is huge because a lot of things are powered by electric motors. Motors need millions of bearings to convert their power into useful applications.
Because of that, very high quality bearings are available at very low prices. Most of the bearings now sold are cartridge bearings, the same ones used on bikes. A common R6 or 6900 bearing used on a bicycle hub is the same R6 or 6900 bearing used in a motor or skateboard.
Most cartridge bearings have rubber seals that are fixed to the outer race and contact the inner race—providing a seal. When you feel a hub and feel resistance it is mostly that resistance that you feel.
Many people feel that this will slow them down. There are no tests that I am aware of that shows that to be the case. It’s not a measureable amount of resistance on a complete bike. What it does do is keep dirt out and grease in so whatever amount of force it does take to overcome seal resistance is well worth it.
Not all companies use cartridge bearings. Both Shimano and Campagnolo still use cup and cone bearings in their higher end hubs largely because the larger ball bearings (bb’s) are more durable. Most major hub and wheels brands, however, use cartridge bearings.
Cartridge bearings have a number of advantages over cup and cone bearings. They are lighter (because the balls and races are smaller), less expensive and have a very high level of quality (because they are made by the millions), and can be easily be replaced (and when you replace them your replace cup, cone, and bearing all at once.
Ceramic bearings have recently become popular claiming to increase performance. It’s virtually impossible to increase cartridge bearing performance based on ball or race quality. Stock bearings of good quality bearings are incredibly efficient. What ceramic bearings do is lower the contact of the seal (or eliminate it all together) and use lighter lubricants—thereby making them spin better in a finger spin test. The same results could be gained by changing the seals and lubricants in a conventional cartridge bearing.
Professionals frequently remove all of the contact seals and run light oil on their time trial bikes. For them everything matters. If there is any advantage—even if it’s not measureable—they will want it. Six-times world sprint champion Antonio Maspes worried about his hub bearings so much he would boil his bearings in English (he was particular about this) oil.
There are generally two types of bearings used in bikes—radial and angular contact bearings. Angular contact bearings have races that contact the bearing at an angle off perpendicular. Radial bearings have races that contact the bearing perpendicular to the ground. Engineers will tell you the loads of a bicycle are best served by angular contact bearings.
Angular contact bearings can be adjusted which is both a good and bad thing. Good because you can adjust them. Bad because when you tighten your quick release you tighten the adjustment without any final control over the bearing adjustment.
Given the options, almost everyone over tightens bearings in an attempt to adjust out lateral play. To almost everyone, play is bad. But a very slight amount of bearing play is a very good thing because bearings roll better with a slight amount of play.
Radial bearings have a very slight amount of play built into them (they were engineered to have play because engineers know a slight amount of play is a good thing). Because radial bearings are all cartridge bearings (at least on bicycles) they have contact seals (which have been removed in the renderings). These contact seals normally prevent you from feeling that slight amount of play because they contact both races.
With the popularity of ceramic bearings (without contact seals) people can now feel that play and it drives them nuts. The lack of the contact seal also means that they tend to ooze lubricant which only adds to the insult.
People spend enormous amounts of money on bicycle hubs. It makes sense to want the best but in reality, all a hub does is connect the axle (a machined aluminum shaft) with the spokes and rim. In the rear wheel there is a drive mechanism but outside of providing a ratcheting mechanism it does no more. Bearing quality is important but as we can see, excellent bearings are available that are very inexpensive and easily serviced.
That vast majority of quality bicycle hubs are cartridge bearing hubs (leaving aside the cup and cone hubs of Shimano and Campy). What then determines the quality of a cartridge bearing hub?
Stack tolerances. You can engineer a product perfectly but if it’s not made with a quality machine that is well maintained the finished product can be poor. Hubs are mostly turned on lathes. The bearing seats and axles and even the outside hub shell shape are turned. That lathe also is run on bearings that wear out and the machine needs regular maintenance. If it’s not maintained the tolerances in the hub are off.
The image of the rear hub shows a typical radial cartridge bearing rear hub. Most have 4 bearings—two for the hub shell and two for the cassette body. If a hub is not machined to high tolerances the bearing cup bores will not be properly aligned. Since the larger diameter of the cartridge bearings are press fit into the hub and cassette body, the inner, slip fit races are free to slide. If the tolerances on the outer races are off, the inner races will not be properly aligned.
If they are free to slide, how can they get out of alignment? Because hubs are designed to lock the lower races together in a series with the end caps, axle bosses, and spacers.
If the hub is drastically out of spec (or the bearings have not been properly pressed) you will feel a rough bearing. If they are slightly out of alignment you may not feel anything unusual but the bearings will wear out quicker.
Unfortunately most bike shops don’t have the proper press fitting tools to properly align and press fit bearings (although more tools designed for this purpose are now becoming available). Many rely on socket wrenches which will press in a bearing but without much regard as to how well it seats. Luckily there is a fair amount of room for error and in the worst case, the bearings (the only thing that will wear out with a poor press fit) are relatively inexpensive.
When I first started setting up high end wheel building in Taiwan about 15 years ago, there were only a couple of quality hub makers. Now there are many. It was about that time that China began stealing low end business from Taiwan (and many Taiwanese makers set up factories in China to make their low end) and the Taiwanese improved the overall quality of their products.In summary, very good hubs are now becoming available at very affordable prices because quality bearings are inexpensive and because more and more makers have increased the quality of their hub making. You can spend a lot of money upgrading hubs without getting any increased performance.
Thanks for reading —John Neugent
John Neugent was was one of the first to establish quality hand building in Taiwan around the turn of the century. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price.