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Gasoline Direct Injection (GDI)

A fuel injection system in which petrol is injected directly into the combustion chamber at high pressure, enabling improved charge cooling, combustion control, and efficiency. See: Gasoline Direct Injection Systems

Gear Ratio

The ratio between input and output rotational speeds in a transmission or final drive, defining torque multiplication and vehicle speed characteristics. See: Gear Ratios and Torque Multiplication 

Gearbox

​A mechanical assembly providing multiple gear ratios to match engine operating characteristics to vehicle speed and load requirements. See: Manual and Automatic Transmissions

Generator (Alternator)

An electrical device driven by the engine that produces electrical current to power vehicle systems and charge the battery

Glazing (Brake

A condition in which brake friction surfaces become smooth and hardened due to heat, reducing effective friction. Indicates thermal stress and poor friction material contact.

Governor (Mechanical)

A device that limits maximum engine or drivetrain speed by regulating fuel, air, or mechanical input. Modern vehicles use electronic control substitutes that integrate with engine management systems

Gradient Resistance

The component of total tractive resistance arising from operating a vehicle on an incline, dependent on vehicle mass and road gradient. See: Vehicle Road Load Forces

Gravitational Acceleration

The constant acceleration due to gravity that influences vehicle load transfer, hill performance, and braking calculations. See: Forces Acting on Vehicles

Gross Combination Mass (GCM)

The maximum allowable combined mass of a towing vehicle and its trailer as defined by the manufacturer. See: Vehicle Mass Definitions

Gross Vehicle Weight

The maximum permissible mass of a fully loaded vehicle including occupants, fuel, and cargo. See: Vehicle Mass Definitions

Ground Clearance

The vertical distance between the lowest fixed point of a vehicle and the road surface, influencing off-road capability and packaging constraints. See: Vehicle Geometry

Guide Vane

A stationary aerodynamic component used in turbochargers and compressors to direct airflow onto rotating elements. See: Turbocharger Components

Gyroscopic Effect

The tendency of rotating masses such as wheels to resist changes in orientation, influencing vehicle stability and steering response. See: Vehicle Dynamics Fundamentals

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