The ABCs of motoring jargon
Our handy guide to vehicle vernacular and geek speak
Do you know the difference between a BEV and a PHEV? Or how a limited-slip differential compares with torque vectoring?
Here’s our useful guide to understanding some of the jargon in the ever-expanding motoring dictionary:
Anti-lock braking system (ABS) — One of the single most effective safety features on modern cars, ABS sends fast pulses of brake force to the wheels to prevent the tyres locking up and skidding. By allowing the wheels to rotate even under hard braking, a vehicle is able to maintain better control when swerving, and it shortens braking distances, particularly on slippery roads.
Traction control — This prevents wheel spin by either briefly reducing engine torque or applying the brakes. If one wheel begins to lose traction, the computer reduces power to the spinning wheel and transfers some force to the non-spinning wheel.
Electronic stability control (ESC) — An advanced form of traction control that uses multiple sensors — including an accelerometer, steering angle sensor, wheel speed sensors and a yaw rate sensor — to help keep vehicles pointed in the right direction. It has many names, including dynamic stability control, electronic stability program and vehicle stability control, but they’re all the same thing.
All-wheel drive (AWD) — Although “AWD” and “4WD” are sometimes used interchangeably, AWD is more commonly applied to vehicles that have full-time drive to both the front and rear axles (such as Audi’s quattro system), either in a fixed split or one that varies according to driving and road conditions.
4WD — Usually applies to offroad-focused vehicles such as 4x4 bakkies and SUVs in which the driver can manually select between two- and four-wheel drive. Why not just permanently have four-wheel drive and enjoy the traction benefits? Because sending drive to both axles uses more fuel.
Differential — Having the driven wheels turning at the same speed works fine in a straight line but not in corners, where the outside wheel has to travel a greater distance than the inside one. A differential is a set of gears that allows the outside wheel to turn faster than the inside one so the vehicle can go around corners smoothly.
Differential lock — Usually used in offroad vehicles, the diff lock provides equal power to the left and right driven wheels so that, even in uneven-surface situations where one of the driven wheels loses contact with the ground, the other wheel will still propel the car forward (a regular unlocked differential transfers all the power to the wheel in the air).
Limited-slip differential (LSD) — This allows the left and right driven wheels to turn at different speeds just like a simple differential, but when one wheel starts to spin faster than the other one, clutches engage to slow the spinning wheel and transfer power to the other. It’s mostly used in high-performance cars to reduce understeer in corners.
Torque vectoring — Like an LSD it transfers or “vectors” engine torque between the vehicle’s left and right wheels, but it’s a more advanced computer-controlled system that works in conjunction with the electronic stability control to either brake or provide more drive force to individual wheels. By braking the inside wheel (which tends to lift and lose traction during high-speed cornering), and providing more drive to the outside wheel (which is being pressed into the road), it allows the car to corner faster.
Continuously variable transmission (CVT) — Instead of gears there are two cone-shaped pulleys connected by a belt. The engine turns one pulley. The other one is connected to the rest of the transmission to the wheels. The size of the pulleys can change from small to large and infinite sizes in between. It provides a step-free power delivery but can also lead to engine droning and a “slipping clutch” effect.
Turbo — A device that uses the exhaust gas to drive a turbine that pushes more air into the engine cylinders to allow them to burn more fuel each second — much like blowing on a fire. Turbos can significantly boost engine power without a major weight increase, which is what makes them so popular.
Twin turbo or biturbo — The trouble with big turbos is they don’t work well at low engine speeds. They take long to spool up, which causes the delayed power response known as turbo lag. Two smaller turbos spool up quicker than a single large one. Sometimes a smaller turbocharger is used to reduce lag at lower rpm, while a larger one takes over to boost power at higher revs.
Twin scroll turbo — This is a two-in-one turbocharger that’s less costly and complex than using two turbos, but also optimises power delivery across the rev range.
Variable geometry turbo — This uses movable vanes that change their angle to alter the airflow of the exhaust gases to maximise boost across the entire engine speed range. It essentially acts as a smaller turbo at low engine revs and a big turbo at higher rpm.
Battery-electric vehicle (BEV) — BEVs like the Nissan Leaf and Tesla are solely powered by electricity, using batteries to power an electric motor. They’re charged with a cable at wall sockets or special fast-charging boxes.
Hybrid vehicle — Hybrids such as the Toyota Prius pair an internal combustion with an electric motor as a way of improving performance and fuel economy, and reducing emissions. They can draw on both sources separately, or at the same time if extra power is needed. The battery is charged by the engine.
Plug-in hybrid vehicle (PHEV) — Similar to a regular hybrid, except the batteries can also be charged by cable.
Fuel cell vehicle (FCV) — Hydrogen and oxygen are mixed inside a fuel cell stack to produce electricity, which powers an electric motor. Water vapour is the only emission. A small number of car companies are investing in FCVs, including Honda with its FCX Clarity and Toyota with its Mirai.