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.

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.The real test of these fag 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.

Now, even a good seal cannot keep out water that’s exerting pressure on the seal. So if you’ve driven through hub deep water your bearings should be cleaned and repacked if they’re serviceable. If you have factory sealed ball bearings, you just need to watch for signs of premature failure.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 ball within some sort of container. Modern hybrid ceramic sealed ball 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 koyo bearing, the greater the cost, but there are some advantages.

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 ball bearings. The outboard bearing protrudes about four millimeters and indexes the driver into a sleeve beneath the cassette's smallest cogs. 

Front sealed ball bearings, go in from the frint and push it against the first clip. Next part is seal, push in from the inside against the clip, flat part of the seal to the clip..There should be a shoulder or another clip to keep the inner bearing from moving forward and letting the crank web hit the case.  No reason for the seal if good "sealed ball bearings"  are used on the crank..NSK brand with brown rubber seals....Beware of Chinese sealed ball bearings with black rubber seals, they can't hold the case pressure necessary