Wheel bearing (hub bearing)
Definition
The wheel bearing lets the hub rotate on the knuckle with minimal friction while carrying the vehicle's weight and cornering loads; modern cars use sealed double-row ball or tapered roller units pressed into the knuckle or bolted on as a complete hub, often with the ABS magnetic encoder built into the seal. Bearings fail from water and grit past the seal, impact damage from potholes and kerbs, incorrect pressing that loads the inner race, and over-tightened or under-tightened hub nuts. The classic symptom is a hum or growl that rises with road speed, changes when swerving (loading one side) and does not change with engine speed or gear; later the wheel develops play felt at 12 and 6 o'clock and heat after driving. Confirm by spinning the wheel on a lift and listening with a chassis ear or feeling roughness through the spring, and compare the four wheel speed signals - a failing encoder bearing sets ABS codes before it makes noise. Replacement often requires a hydraulic press and the hub nut torqued to a high, exact value, sometimes with a new stretch bolt. Codes: ABS wheel speed sensor codes C0035-C0050 when the encoder ring is damaged or the air gap grows, otherwise none.