- by Christopher Jones
- Published: 20 August 2012
You will find ball bearings in various places on your bike: the headset, the cranks and the hubs of your wheels (and even more places in full suspension mountain bikes). For this review we are concentrating on the bearings in your bicycle wheel hubs for two reasons. Firstly, this is where you would see the most obvious improvement in performance with an upgrade, and secondly, there were no bearings available in the size we needed for our bottom bracket and headset from Boca Bearings.
Boca Bearing are a US company who specialise in ceramic bearings for industrial, mechanical and sporting applications. You would probably only consider purchasing bearings for your bike if you had a wheelset that was a little old and needed an overhaul, or if you are a high performance cyclist and want more (or really less) than a standard wheelset will offer in terms of rolling resistance.
Bearing replacement is usually the domain of professional bike mechanics and while it is still possible to do it yourself, you need to be confident in your understanding of hubs, as it is fairly easy to make a mistake. For this review, Aaron Dunford of Fusion Peak was bought in to be ‘the expert’; he brings years of experience as a bicycle mechanic and wheel builder to this investigation. On top of this, Aaron is also test riding the bearings which are going into his Bontrager MTB wheelset.
Why use a ceramic bearing?
Picture a bearing with balls between the inner and outer surfaces (called races). Traditional bearings use steel balls, either loose between the surfaces or sealed within some sort of container. Modern hybrid ceramic sealed bearings have ceramic balls inside steel races. Full ceramic bearings have the inner and outer races also in ceramic. The more ceramic components in a bearing, the greater the cost, but there are some advantages.
Ceramic balls are lighter than steel balls and roll faster. This means there will be less friction in the bearing, resulting in lower generated heat and a lower rolling resistance. It also means a longer life span.
The advantages of ceramic bearings are often viewed as a myth and, the fact is, even an experienced cyclist will find it hard to physically sense a difference between different bearings on their bike, all other things being equal.
Getting the right size
We faced our first challenge early on in simply getting the right bearings from Boca. An average rear wheel hub has three bearings and the front has two bearings; the tricky thing is that these bearings can be of different sizes and each bearing brand does sizing differently. To make it even harder, each wheelset model from a brand can use different sized bearing and even a new year’s model (from 2011 to 2012, for example) can mean different sizes.
To help with this complexity, the Boca Bearings website allows you to select a wheel brand and exact model in order to get the right sized bearings. For each bearing size you will find the different types of bearings available: chrome, steel, hybrid ceramic, and complete ceramic. For bearing selection, the important dimensions are the inside diameter, outside diameter and the width, so vernier calipers are particularly useful in measuring your current bearings first.
For the Mavic Ksyrium road wheels we were initially going to use in this review, we had the bearing dimensions but couldn’t match the model nor find all of the bearing sizes on the Boca site. We then tried to find bearings for some Bontrager mountain bike wheels and, though these wheels were not listed, we found matches for four of the five bearings, so we ordered them.
The ceramic hybrid bearings we received were three yellow sealed SMR6000C-2YS/C3 (ID 10mm OD 26m Width 8mm) bearings at US $17.95 each, and another yellow sealed SMR6900C-2YS/C3 (ID 10mm OD 22m Width 6mm) bearing at the same price. For the fifth bearing, the size was not a common one and only a chrome bearing was available, a little cheaper at US $11.95. This will be a good control bearing that we can later use for comparison.
Preparation before bearing installation
After a lot of planning it was time to get our hands dirty. We pick up the action with the old bearings already removed. Before considering getting the new bearings in, the hubs first need to be prepared, particularly if the wheels have already seen a bit of action. A good clean with a rag will get any grit out and a blade can be used to remove any burrs inside the hub and at the hub ends, so that metal shavings aren’t pressed inside when the bearings are fitted. After a coating of light oil (as opposed to grease) the hub is ready. The key to pressing in the bearings is to press them in perfectly straight, so don’t even think about using a hammer.
Removing the old bearings and fitting the new ones requires specialist tools and, since all hubs are different, there is no single tool that will do it all. Aaron Dunford is mechanically adept and he had built some of the tools we needed for this job. Some tools were as simple as nuts and washers on a quick release skewer combined with the old bearings to safely press the new ones in; the quick release is used to slowly leverage them into place. Where the skewer doesn’t work, a long threaded bolt with properly placed washers and nuts becomes a tool that can hold the new bearing properly in place as a spanner slowly tightens to press the bearing in. Does it sound like DIY? Well it is, but in the hands of an experienced mechanic.
Fitting the bearings in the rear hub also means rebuilding the freewheel, and putting everything together the right way and in the right order. Having a professional rebuild the freehub and fit the bearings will give you peace of mind, given that a mis-pressed bearing could damage the hub and ruin the wheel.
When we tested the Bontragers with the new bearings, the difference in rolling resistance was profound. It is a great sign when you can softly spin a wheel and watch it rotate for ages. The original bearings had already suffered years of abuse on sandy trails; for a brand new wheelset you may however find that the noticeable difference is marginal.
So how do these bearings ride? Let’s check with Aaron after he completed 500km with his Bontrager wheels and new Boca Bearings:
“Since the first ride I did notice a big difference in control and speed. I quickly accepted this as the new norm. From the first rides I felt that I could let the bike roll off drops with less pulling up, I could pump the wheel in the front end to pre load it and with the new bearings the wheel went forward instead of slowing due to the increase in friction. Also, at very slow speeds, my balance was notably better due to the ease at which the bike rolls. When doing a track stand, the response in the wheels to rocking gently is very precise and light feeling. So far I can feel no wear or hear any crunching.”
The yellow seal hybrid ceramic bearings are at the affordable end of the scale when compared with full ceramic bearings that will set you back US $60 – $80 a piece.
The real test of these bearings is the test of time, and these wheels are due to see some good action both for training and competitive events on local and Canadian soils. Stay tuned, as we will return to these wheels in about six months and take them apart. In the meantime, you can take a closer look at the Boca Bearings for Cycling on their website.
Video of the bearing installation
During the bearing installation we ran a video camera and have packed it together in a super fast video.