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A look at the XD driver's three-pawl ratchet shows the stiff, flat springs and the unique, three-tooth engagement on each pawl. Threads on the driver (right) engage a sleeve inside the eleven-speed cassette. The driver has two [sealed bearings] . The outboard bearing protrudes about four millimeters and indexes the driver into a sleeve beneath the cassette's smallest cogs. 

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.

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 fag bearings on their bike, all other things being equal.

We faced our first challenge early on in simply getting the right bearings from Boca. An average rear wheel hub has three skf 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 wheel set 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.