The vast majority of bicycle wheels use a type of hub known as «cup and cone», as shown on the right above. This type of hub is easy to service, but requires extremely careful adjustment to reduce friction and extend lifespan.
The cups are built into the shell of the hub; the cones are conical nuts that screw onto the axle. Steel balls roll between these two parts. The combination of cup, cone and balls forms the bearing; there is a bearing on each side of the hub.
If the cones are screwed on too far, they exert pressure on the bearing balls. This causes excessive friction; the wheel will not turn as freely as it should, and the parts will wear out prematurely.
If the cones are not screwed on far enough, the bearings will have «play»: the wheel will be able to shake back and forth on its bearings. This is an unpleasant sensation, and may cause control problems.
This adjustment is very critical; corrections on the order of 1/10 of a turn or less are needed to get the optimal adjustment.
Quick-Release Hub adjustment
Many people undertighten quick release skewers. You can sort of get away with this, because most newer bikes have vertical dropouts in the rear, so the wheel won't slip forward under load. In the front, we have the execrable «lawyer lips» to defeat the purpose of the quick release. This is still not a good idea, because the compression
To check your bearing adjustment, put the wheel into the bike with the quick release just barely tight enough to keep the wheel from falling out. If you are working on the rear wheel,
Try to wiggle
Once you have seen how the wheel turns with the quick release loose, try tightening the QR, then check again. If your bearing adjustment is correct, the play will disappear, but the wheel will turn as freely as it did when it was too loose. For very fine tuning of this, you can slightly vary the adjustment
This is not an issue
The flats that let you turn the cones are usually quite shallow, so you will need at least one, preferably two special cone wrenches. Most front hubs require 13 mm cone wrenches, most rears take 15 mm. For most cyclists, the best choice
For shop use,
Cone wrenches are very thin for their size, and should not be used for anything other than cones. Even when used properly, these are basically consumable tools, not a «lifetime investment» as with My major hub tools
The same approach works for conventional rear hubs if the freewheel is off.
For cassette hubs, or conventional rear hubs that I want to adjust without removing the freewheel, I use a thin 15 mm wrench and the two 17's.
To loosen this type of hub, I usually do have to loosen the left locknut from it's cone, loosen the cone,
Special tool for rapid cone adjustment under load
I have made a special tool for cone adjustment on QR hubs, consisting of a skewer and a spacer bushing to allow the handle end of the skewer to press against the end of the axle, leaving the locknuts unobstructed. This is very handy, saves a good deal of time in the shop. Since it presses directly on the ends of the axle, you can make the actual adjustments while the axle is under compressive load from the quick release. This has not previously been possible.
The spacer bushing consists of an old,
Solid Axle Hubs
The quick check for rear bearings is to slowly backpedal with the bike off the ground. Depending on the degree of freeness of the freewheel, a properly adjusted wheel will either «pendulum» as a front wheel does, or, if the freewheel is a bit gooey, the wheel will turn backwards. If the wheel just sits there, the bearings are too tight (or the brake is rubbing!)
Poor cone adjustment is not usually obvious to a customer, but it is really quite important. If a hub is too tight, the bearing surfaces will self destruct prematurely, and the bike will not roll as freely as it should.