3.1 Road wheels

• The functions of wheels in a vehicle
• Types of tyres (tube and tubeless)
• Ply orientation: radial and cross-ply tyres
• Interpreting tyre sidewall specifications

• explain the functions of wheels in a vehicle
• identify types of tyres used in vehicles
• illustrate types of ply orientation used on vehicle tyres
• interpret specifications on tyre sidewalls
• appreciate the role of tyres in vehicle operation

“What role do the wheels and tyres play in a vehicle?”

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1. Road wheels and tyres
   40 min · 1 practice tasks · quiz
   The functions of a vehicle wheel and tyre, the types of tyre (tube and tubeless), radial and cross-ply construction, how to read tyre sidewall markings, and the safety-critical role of tyres.
2. Functions of the road wheel
   40 min · 1 practice tasks · quiz
   The wheel and tyre carry the vehicle, grip the road, transmit drive and braking, cushion bumps, and allow steering - they are the only contact with the tarmac.
3. Rims and wheel construction
   40 min · 1 practice tasks · quiz
   The rim is the metal wheel: drop-centre well, flanges for the beads, steel or alloy. Rim diameter in inches must match the tyre.
4. Tube tyres
   40 min · 1 practice tasks · quiz
   A tube tyre has a separate inner tube that holds the air. The cover takes the wear. Punctures often go down fast. Still used on some bikes, trucks and unsealed rims.
5. Tubeless tyres
   40 min · 1 practice tasks · quiz
   A tubeless tyre has no tube: the liner and the bead-to-rim seal hold the air. Punctures often leak slowly. This is the common car tyre, and it needs a true rim.
6. Radial ply tyres
   40 min · 1 practice tasks · quiz
   Radial cords run bead to bead. Belts under the tread hold the footprint. The tyre is flexible, cooler and longer-lasting - almost all modern cars, marked R.
7. Cross-ply tyres
   40 min · 1 practice tasks · quiz
   Cross-ply (bias) cords criss-cross at an angle. The tyre is stiffer and builds more heat. Older type; do not mix with radials on the same vehicle.
8. Reading tyre size on the sidewall
   40 min · 1 practice tasks · quiz
   On 195/65 R15, 195 is width in millimetres, 65 is aspect ratio, R is radial, 15 is rim diameter in inches. Size must match the vehicle.
9. Load index and speed rating
   40 min · 1 practice tasks · quiz
   After the size, 91H means load index 91 (about 615 kg per tyre) and speed letter H (210 km/h). Never fit a lower rating than the vehicle specifies.
10. Tyres on Kenya roads
    40 min · 1 practice tasks · quiz
    The inquiry: wheels and tyres are the only contact with the road. On Kenyan roads that means correct pressure, legal tread, no damage, and the right tubeless radial size - every day, not only in an exam.