Wheels and Tires
Domain focus
This domain covers tire construction, size and load ratings, tubes and tubeless rims, pressure, balance, runout, spokes, and axle service. The exam expects you to decode a sidewall and connect wear patterns to pressure, alignment, or suspension.
Core rules
- A tire size such as 180/55 ZR17 73W means 180 mm section width, 55% aspect ratio, radial construction, 17-inch rim, load index 73 (365 kg per tire), and speed rating W (270 km/h). ZR indicates a radial tire rated above 240 km/h.
- The DOT date code gives the week and year of manufacture; for example, 2319 is the 23rd week of 2019. Age, cracking, and flat spotting matter even when tread remains.
- Check pressure cold and set to the motorcycle manufacturer's specification, not the maximum on the sidewall. Recheck hot pressure only for information.
- Tube-type and tubeless rims are not interchangeable. Use a new tube and valve stem when mounting a tube-type tire; inspect the rim band and spoke ends.
- Balance the wheel after mounting and check axial and radial runout. Spoke wheels need even tension and true rims.
- Torque the axle and pinch bolts to specification and confirm brake and wheel-speed sensor alignment.
Worked example
A tire is marked 180/55 ZR17 73W and 2319. The technician calculates a sidewall height of about 99 mm (55% of 180 mm), confirms the load index is 365 kg per tire, and notes the tire was made in the 23rd week of 2019. The tread is 3 mm, but the sidewalls show cracking and the tire is more than six years old. The technician recommends replacement because aged rubber can fail even with legal tread. The new tire is mounted in the direction arrow, balanced, and set to the cold pressure specified for the bike.
Traps
Using the sidewall maximum as normal pressure; checking pressure only when hot; mixing bias and radial tires; reusing a tube; skipping valve-stem replacement; over-tightening the axle; adding excessive balance weight; mounting a tire backward; and repairing a sidewall puncture.