Grade 10 power mechanics Motor Vehicle Systems – Road Wheels Notes

1. Identify and outline sub-sub-strands:
   • Functions of wheels in a vehicle
   • Types of tires used in vehicles
   • Types of ply orientation in tires
   • Interpretation of tire specifications in relation to road safety
   • Importance of tires in vehicle operations
2. Explain the functions of wheels in a vehicle.
3. Identify types of tires used in vehicles.
4. Illustrate types of ply orientation used on vehicle tires.
5. Interpret specifications on tire sidewalls in relation to road safety.
6. Appreciate the role of tires in vehicle operations.

1. Functions of wheels and tyres

• Support vehicle weight: wheels and tyres carry the load of the vehicle and passengers.
• Provide traction: tyres grip the road so the vehicle can accelerate, brake and corner safely — very important on wet Kenyan roads or during rainy seasons.
• Absorb shocks: tyres and wheels help smooth out bumps from potholes and rough surfaces common on many Kenyan roads.
• Transmit drive and braking forces: wheels transfer engine power to the road and braking force from brakes to slow the vehicle.
• Steering control: front wheels (or all wheels for some vehicles) allow directional control.

2. Types of tyres (common types in Kenya)

• Radial tyres: most common for passenger cars — better fuel economy, ride comfort and longer life.
• Bias (cross-ply) tyres: older style, sometimes used on heavy farm vehicles and some commercial transports.
• Tubeless tyres: modern cars and matatus — less chance of sudden air loss.
• Tubed tyres: still used on some trucks and motorcycles.
• All-season tyres: designed to perform in a variety of conditions — common for everyday use.
• Off-road / All-terrain (AT) tyres: for SUVs and pickups used on rough Kenyan roads, bush tracks.
• Commercial / Heavy-duty tyres: used on buses, trucks and matatus — built for high loads and durability.

3. Types of ply orientation — simple illustration

Tyre carcass plies are layers of fabric or steel that give strength. Main types:

• Bias (cross-ply): plies laid at alternate angles (e.g., 30–40°) across the tyre — flexible sidewalls, used on older tyres.
• Bias-belted: bias-ply carcass plus stabilising belts under the tread for better high-speed stability.
• Radial: cords run radially (90° to the direction of travel) from bead to bead; steel belts under tread for strength and grip.

4. Reading and interpreting tyre sidewall specifications (safety focus)

Tyre sidewalls contain important information. Example:

• 175 — tyre width in millimetres (distance across tread).
• 65 — aspect ratio; tyre height is 65% of width.
• R — radial construction.
• 14 — rim diameter in inches (the wheel size it fits).
• 82 — load index (each tyre’s maximum load). You use a load index chart to convert to kg (e.g., 82 ≈ 475 kg per tyre).
• T — speed rating (maximum safe speed for the tyre construction; T ≈ 190 km/h). Use the rating for selecting appropriate replacement tyres.
• DOT 2419 — manufacture date code: 24 = week, 19 = year (week 24 of 2019). Older tyres become unsafe even if tread remains.

Safety notes: check sidewalls for: tread depth (wear bars), tyre age (DOT code), maximum inflation pressure and load limits, cuts or bulges, and matching sizes on axle pairs (front or rear).

5. Importance of tyres in safe vehicle operation (Kenyan context)

• Road safety: worn or under-inflated tyres reduce grip — increased stopping distance on wet/loose surfaces (puddle, mud, highway rain).
• Fuel economy: correct tyre pressure reduces rolling resistance and fuel consumption — important for matatu and boda-boda operators.
• Load carrying: proper tyres and correct load index prevent blowouts when carrying goods or passengers on Kenyan highways.
• Comfort and vehicle wear: properly matched tyres reduce vibration and wear on suspension and steering parts — fewer repairs and safer journeys across rough roads.

6. Basic maintenance and safety checks (quick checklist)

1. Check tyre pressure weekly (or before long trips). Follow vehicle placard or tyre max pressure on sidewall.
2. Inspect tread depth: use a coin or ruler. Replace tyres when tread is low or when wear bars show.
3. Look for cuts, bulges, nails or foreign objects. Repair or replace as needed.
4. Check tyre age (DOT code) — consider replacement for tyres over 6 years old or per manufacturer guidance.
5. Rotate tyres regularly and check wheel alignment and balancing after hitting big potholes.
6. Always carry a serviceable spare and tools; practise changing a wheel safely (use hazard triangle on Kenyan roads).

Suggested Learning Experiences (classroom & fieldwork)

• Sidewall decoding activity: give learners printed tyre sidewalls (photos) and have them decode width/aspect/rim/load/speed/DOT codes in groups.
• Tread-depth practical: bring an old tyre and a ruler; students measure tread depth at several points, identify wear bars and make a short report.
• Pressure and inflation demo: visit the school compound or local garage; demonstrate checking pressure with a gauge and show effects of under/over inflation using simple measurements or ride comfort test.
• Ply orientation drawing: students sketch cross-sections to label bias vs radial plies using the diagrams above as models.
• Field visit: arrange a short visit to a reputable tyre workshop or VTI (Vehicle Inspection) centre to see tyre selection, balancing, and wheel alignment in action.
• Awareness project: groups prepare a short safety poster/presentation (for matatu drivers, boda-boda riders or parents) explaining tyre checks for Kenyan roads.
• Role play & quiz: simulate roadside tyre inspections and ask learners to recommend safe actions (e.g., do not drive on a bulging tyre; replace before long trip).

Summary

Wheels and tyres are critical to safe and efficient vehicle operation. Learners should be able to identify tyre types, read sidewall specifications, understand ply orientation, and carry out basic safety checks — especially important on Kenyan roads where potholes, heavy loads and rainy seasons increase tyre risk.