How do I know if my motorcycle bearings are bad?

The following is a practical guide for determining whether motorcycle bearings are damaged:

Abnormal noise identification
Wheel hub bearings: During driving, a continuous low-frequency "buzzing" or "roaring" sound is heard, which increases with the speed of the vehicle and still exists when sliding.
Steering column bearings: make a "click" sound or metal friction sound when turning at low speeds, especially when the handlebars pass through the neutral position.
Engine bearings: There is a rhythmic "dada" knocking sound (different from valve sound) in the idle or low-speed range, which varies with the speed.

Changes in rotational resistance
Wheel bearings: When lifting the wheel and manually rotating it, you may feel stuck, blocked, or experience a sudden increase in resistance in certain areas (compared to the wheels on both sides).
Chain tensioner bearing: When the rear wheel is turned off, periodic "rustling" friction sound or unsmooth rotation can be heard.
Component loosening detection (axial/radial shaking)
Wheel detection: After the wheel is off the ground, hold the top and bottom of the tire with both hands and shake it vigorously, feeling axial movement (note: the suspension must be ruled out of looseness).
Steering column inspection: Support the front of the vehicle with the main bracket, hold the front brake and press down on the handlebar to test the bearing pre tension. If the front of the vehicle shows a "nodding" looseness, it needs to be adjusted or replaced.
Rear rocker arm detection: Apply lateral force to push and pull the rear wheel, and observe whether there is displacement at the connection between the rocker arm and the frame (excluding loose chain links).

Seal failure traces
Dry black oil sludge, fresh lubricating grease leakage or rust water stains (especially obvious after rain) were found around the bearing housing.
The rubber sealing ring is visibly cracked, hardened, deformed, or detached from the slot.
Thermal imaging anomaly (advanced judgment)
After long-distance driving, use an infrared thermometer to compare the temperature of the wheels on both sides of the coaxial cable - the temperature of the wheel hub where the damaged bearing is located is significantly higher than that on the other side (caution should be taken if the temperature difference exceeds 15 ℃).

Abnormal response of related components
Damaged wheel hub bearings may cause brake disc misalignment, manifested as handlebar shaking during braking.
Wear of the steering column bearing can cause unstable straight-line driving of the vehicle (similar to tire roundness).

Extreme failure symptoms
The wheels suddenly swing violently while driving (stop immediately!)
The bearing area emits a burnt smell or smoke (high-temperature carbonization of lubricating grease).