A bicycle has bearings in three places, the wheel hubs, the bottom bracket where the pedal cranks attach and the headset that steers, and all use the same principle: steel balls rolling in a cup-and-cone race packed in grease. Service hubs every 3-6 months of regular riding or whenever the wheel feels rough or loose, clean everything, replace any ball or race with a flat spot, crack or pit, then adjust until there is no play but no binding.
Part of Bicycle Repair & Fabrication
Bicycle bearings are rings of steel balls held between a cup and a cone in grease, in the hubs, the bottom bracket and the headset.
How Many Times The Balls Roll
A bearing does a great deal of rolling between services. Assume a rider covers 10 km a day (an assumed figure) and the wheel circumference is 2.1 m:
- Revolutions per km = 1,000 / 2.1 = 476
- In 3 months (about 90 days, 900 km) = 900 × 476 = about 430,000 revolutions
- In 6 months (1,800 km) = about 860,000 revolutions
Each of those turns carries the load through every ball in turn, so a ball or race with a small pit or flat spot gets worse quickly, because the next revolution rolls the same flaw under load. This is why the parent article’s interval is a few months.
The Principle: Cup, Cone, Balls, Grease
Each bearing has a cup (the fixed outer race, pressed or threaded into the hub shell, bracket shell or head tube), a cone (the threaded inner race on the axle or spindle), and a ring of steel balls between them, packed in grease. Turning the cone in or out adjusts how snugly the balls are held: too loose and the part clunks; too tight and it grinds and wears.
The parent article gives the counts: usually 9 or 10 balls per side in a wheel hub, and about 11 per side, 1/4 inch each, in a bottom bracket.
Where Each One Is Done
- Wheel hubs: Wheel Hub Bearings
- Bottom bracket: Bottom Bracket
- Headset: Headset Bearings
What You Need
- Wrenches that fit the cones and locknuts, and a cone wrench or thin spanner
- A special wrench for bottom bracket lockring and cup
- Solvent: kerosene, alcohol or similar, and a rag
- Grease, and a small cup to catch balls
- A magnet or tweezers to pick up balls
Method: The Same Five Steps For All Three
- Open it and catch every ball in a cup. Count them, so you know how many go back.
- Clean balls, cups and cones with a rag and solvent.
- Inspect. Any ball with a flat spot, crack or pit must be replaced. Check the cups and cones for pitting, which looks like small dull craters on the polished track.
- Pack with fresh grease, then seat the balls into it.
- Adjust until the part turns freely with no play, then lock the adjustment without disturbing it.
Common Mistakes
- Losing a ball, or putting back fewer than came out — a ring that is short of balls runs unevenly.
- Reusing pitted balls — the pits grow and the race is ruined.
- Locking without checking — tightening a locknut against a cone often squeezes the cone further; check the feel after locking.
- Overtightening — a bearing set tight wears itself out.
Safety
Flammable solvents and loose parts
Kerosene, alcohol and especially gasoline give off vapour that ignites from a flame or spark (Gasoline); clean parts outdoors, with no flames nearby, and keep the cleaning rag away from heat. Bearing balls roll off benches and are easy to swallow or slip on; work over a tray or cloth. After any bearing service, test the brakes and steering at walking pace before riding.
What’s Next
- Learn next: Wheel Hub Bearings — the commonest service
- Combine with: Tire & Wheel Care — the rest of the wheel