Automobile Fundamentals and Workshop Safety
This domain tests whether you can describe how a road vehicle is laid out and whether you can work on one without hurting yourself, the vehicle or the workshop. Expect definitions of chassis, wheelbase, track, kerb weight, gross vehicle weight, payload and turning circle radius, plus straight recall lists: PPE, fire-extinguisher classes, jacking precautions and housekeeping rules.
Chassis and vehicle terms
- Chassis (rolling chassis) = frame + engine + transmission + axles + suspension + wheels, without the body.
- Wheelbase: centre of the front axle to centre of the rear axle. Track: distance between the centre lines of two wheels on the same axle.
- Kerb weight: ready to drive with all fluids and full fuel, no passengers or luggage. GVW = kerb weight + payload.
- Turning circle radius depends mainly on wheelbase and the maximum steer angle.
Workshop safety rules
- PPE: safety goggles, gloves, safety shoes, ear plugs, and a mask when painting or grinding.
- Support a lifted vehicle on axle stands; a jack alone is a crush hazard.
- Fire classes: A paper/wood, B petrol/oil, C gas/electrical, D metals. Use CO2 or dry powder on fuel and electrical fires; never water on burning petrol or live electrical equipment.
- Charge lead-acid batteries only in a ventilated area, away from sparks - they release hydrogen.
Worked example
A vehicle has a wheelbase of 2.5 m and a maximum front-wheel steer angle of 30 degrees. Approximate turning radius to the inner wheel centre is R = wheelbase / sin delta = 2.5 / sin 30 = 2.5 / 0.5 = 5 m. Add about half the track (say 0.75 m) to reach the outer wheel path. Reasoning: sin 30 = 0.5, and a longer wheelbase or a smaller steer angle both enlarge the circle, which is why long trucks need a wider road to U-turn.
Traps that cost marks
Wheelbase is not track. Kerb weight is not GVW. CO2 extinguishers are useless on burning magnesium or sodium. Never work under a vehicle held only by a hydraulic jack, even with the wheels chocked.