Wheels, Hubs, Bearings, and Tires
What the candidate must know
Cover wheel types (disc, spoke, aluminum), lug nut torque and tightening pattern, hub and drum mounting, inner/outer wheel bearings, seals, bearing adjustment, and ABS tone rings. Tire knowledge includes load range/ply rating, speed rating, inflation, tread depth, sidewall inspection, matching duals, and TPMS on newer buses. Know radial runout, lateral runout, and balance as causes of vibration, and understand that dual tires must match in diameter to prevent overload and heat.
Traps in questions
- Forgetting that lug nuts must be torqued to spec in a star/cross pattern and rechecked after a short drive; over-torque stretches studs and distorts drums.
- Mismatching dual tire diameters - a difference in circumference causes the smaller tire to be overloaded and drag.
- Confusing bearing noise (changes with cornering load) with tire noise (changes with speed and road surface).
- Ignoring ABS tone ring damage when servicing hubs.
Rule of thumb / worked example
For a vibration complaint, road-test to identify speed range, then inspect for runout and balance. A vibration that appears at a specific speed and changes when the wheel is loaded in a turn often points to a wheel bearing; a vibration present across a speed band with no load sensitivity points to tire/wheel balance or runout. Always verify lug torque and dual tire match before condemning bearings.