Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Road Wheels and Tyres
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Road Wheels and Tyres
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Subject: Auto Mechanical Works
Class: Senior Secondary 2
Term: 2nd Term
Week: 2
Theme: Transmission And Breaking System
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Identify different typesand sizes of wheels and tyres State causes of tyre wearand explain the effects of car pressure on tyrebehaviour Sketch and differentiatebetween radial and cross-plytyres Check and adjust tyrepressure to the manufacturer's specification
The road wheels and tyres work in conjunction to perform several crucial functions for a vehicle: Support Vehicle Weight: They bear the entire weight of the vehicle, its passengers, and cargo.
Provide Traction: The tyre tread pattern creates friction with the road surface, allowing the vehicle to accelerate, brake, and corner effectively.
Absorb Road Shocks: The tyre's air pressure and flexible sidewalls, along with the wheel's design, cushion the impact of road irregularities (potholes, bumps), providing a smoother ride and protecting the suspension system.
Facilitate Steering and Direction Control: The wheels provide the pivot point for steering, while the tyres respond to steering inputs, guiding the vehicle in the desired direction.
Enable Braking: The tyres transmit braking forces from the brake system to the road, slowing and stopping the vehicle.
Maintain Ground Clearance: They lift the vehicle's undercarriage off the ground, preventing damage from obstacles. Wheels are typically made from steel or alloy and come in various designs.
Steel Disc Wheels: Construction: Made by pressing and welding steel sheets. Consist of a steel rim (which the tyre mounts on) and a steel disc (which bolts to the hub).
Characteristics: Economical, very durable, often heavier, good for absorbing impacts, commonly found on older vehicles, commercial vehicles (e.g., mammy wagons, some danfos), and as spare wheels.
Appearance: Often covered by hubcaps or wheel trims.
Alloy Wheels (Aluminum Alloy Wheels): Construction: Cast or forged from aluminum alloy, which is lighter than steel.
Characteristics: Lighter weight (improves handling, fuel economy), better heat dissipation (beneficial for braking), aesthetically pleasing, but can be more susceptible to bending or cracking from severe impacts compared to steel. Widely used in modern passenger cars, SUVs, and luxury vehicles.
Appearance: Polished, painted, or machined finishes, typically exposed.
Construction: The fabric plies (typically nylon or polyester) are laid diagonally across the tyre from bead to bead, with successive layers running in opposing directions (criss-crossing) at an angle of 30-40 degrees to the direction of travel. The sidewall and tread are interdependent.
Characteristics: Stiffer sidewalls and tread area. Good resistance to sidewall damage. Often preferred for heavy-duty vehicles, agricultural machinery, and some older vehicles. Higher rolling resistance (less fuel efficient). Less comfortable ride at higher speeds. Tendency for tread distortion during cornering. Shorter tread life compared to radial tyres.
Sketching Differentiation: A teacher's sketch should show criss-crossing diagonal plies extending through both the tread and sidewall areas.
Construction: The fabric plies (e.g., polyester or rayon) run radially (straight across the tyre) from bead to bead, perpendicular to the direction of travel. A separate belt package (made of steel, fiberglass, or aramid) is then laid circumferentially under the tread area to stabilize it. This separates the functions of the sidewall and tread.
Characteristics: Flexible sidewalls and stable tread. Superior grip and handling, especially in wet conditions. Lower rolling resistance (more fuel efficient). More comfortable ride. Longer tread life due to reduced tread squirm. Better heat dissipation. More common in modern passenger vehicles (e.g., Toyota Camry, Honda Accord, Nissan Almera, popular in Nigeria).
Sketching Differentiation: A teacher's sketch should show plies running straight across from bead to bead, with a distinct layer of belt plies directly under the tread.
Tyre sizes are encoded in a standard format: 205: Tread Width in millimetres (mm). This is the width of the tyre's tread from sidewall to sidewall. 55: Aspect Ratio (or Profile) as a percentage. This is the ratio of the tyre's sidewall height to its tread width. (Sidewall Height = 55% of 205mm). A lower aspect ratio means a shorter sidewall (sportier look, better handling, harsher ride). R: Denotes Radial-ply construction. (D for Diagonal/Bias-ply is rare in modern passenger tyres). 16: Rim Diameter in inches. This is the diameter of the wheel rim that the tyre is designed to fit. 91: Load Index. A numerical code representing the maximum weight (in kilograms or pounds) that the tyre can carry at its maximum inflation pressure. (e.g., 91 typically means 615 kg). This is crucial for safety, especially for commercial vehicles in Nigeria which often carry heavy loads. V: Speed Rating. An alphabetical code indicating the maximum speed at which the tyre can safely carry its rated load. (e.g., V typically means 240 km/h). Example Interpretation for a Nigerian Context: A commercial bus (e.g., a Coaster or a large Hummer bus) tyre might be marked "215/75 R 17.5 126/124 L". 215mm tread width. 75% aspect ratio (tall sidewall, good for comfort and load carrying). Radial construction. 17.5 inch rim diameter (common for light commercial vehicles). 126/124 Load Index (indicates capacity for single/dual wheel application). L Speed Rating (typically up to 120 km/h, suitable for commercial vehicles).
This topic has profound real-world relevance, especially in the Nigerian context.
Road Safety and Accident Prevention: Application: A significant number of road accidents in Nigeria are attributed to tyre failure, particularly blowouts caused by under-inflation, overloading, or worn-out tyres. Understanding correct tyre pressure and identifying wear patterns can prevent these incidents. For danfo (commercial bus) and truck drivers, who often overload their vehicles, knowledge of load index and the dangers of exceeding it is critical for preventing catastrophic failures on highways (e.g., Lagos-Ibadan Expressway).
Integration: Mechanics advising vehicle owners on proper tyre maintenance directly contribute to safer roads, reducing fatalities and injuries. This knowledge also empowers drivers to perform basic safety checks, like a pre-trip inspection, reducing their exposure to risks.
Economic Savings and Cost Management: Application: Tyres are a significant recurring expense for vehicle owners and commercial operators in Nigeria. Proper tyre pressure maintenance ensures even wear and extends tyre lifespan, reducing the frequency of costly tyre replacements. Improved fuel efficiency from correctly inflated radial tyres translates to substantial savings on petrol/diesel costs, which are often volatile in Nigeria. For okada (motorcycle taxi) riders and keke Napep (tricycle) operators, who rely on their vehicles for daily income, these savings directly impact their livelihood.
Integration: Students can calculate potential fuel savings over a year for a commercial vehicle by maintaining correct tyre pressure. They can also analyze the economic impact of premature tyre replacement due to neglect.
Career Opportunities and Entrepreneurship: Application: The skills learned are directly applicable to careers as auto mechanics, tyre technicians (vulcanizers), and vehicle inspectors. With a large and growing vehicle population in Nigeria, there is constant demand for skilled professionals in tyre servicing, rotation, balancing, and alignment.
Integration: This topic can inspire students to consider entrepreneurial ventures in tyre repair and sales. They can learn about the process of setting up a tyre service centre (e.g., sourcing equipment, customer service) and identify opportunities in their local communities. ---