Glossary

The terms that come up across the games and the car database, explained properly — what they actually mean and why they matter, rather than one-line dictionary definitions. Each term has its own page with the longer explanation.

engine

Bore and stroke: The cylinder's diameter and the distance the piston travels. A wide bore with a short stroke suits high revs; a narrow bore with a long stroke favours low-down pull.
Camshaft: The shaft whose lobes push the valves open. Its profile — how far and how long each valve opens — does more to shape an engine's character than almost any other single part.
Compression ratio: How much the fuel-air mixture is squeezed before it burns, expressed as the cylinder's volume at the bottom of the piston's travel versus the top. Higher ratios extract more energy from each combustion, but demand higher-octane fuel to avoid knock.
Displacement: The total volume swept by all the pistons, quoted in litres or cc. It's the number in '5.0 V8' — a rough proxy for how much air an engine can move, and historically the basis for tax bands in much of the world.
Flat / boxer engine: Cylinders lie horizontally in two opposed banks, pistons punching away from each other. It sits low, which drops the car's centre of gravity — the reason Porsche and Subaru have stuck with it.
Forced induction: Any system that pushes more air into the engine than it could draw in by itself — turbocharging or supercharging. More air means more fuel can be burned, so more power from the same displacement.
Inline engine: Cylinders in a single row, as in an I4 or I6. An inline-six is inherently balanced — its firing forces cancel out — which is why it feels so much smoother than a V6 of the same size.
Naturally aspirated: No turbo or supercharger; the engine breathes on atmospheric pressure alone. Usually means less peak power for the displacement, but throttle response that tracks your right foot exactly.
Overhead cam (SOHC / DOHC): The camshaft sits above the cylinder head rather than down in the block. Double overhead cam gives each bank two shafts, allowing four valves per cylinder and higher safe revs.
Supercharger: A compressor driven directly off the crankshaft. Because it's mechanically linked to engine speed it responds instantly, but it costs power to spin — you're spending engine output to make more of it.
Turbocharger: A compressor spun by exhaust gas that would otherwise be wasted, which makes it more efficient than a supercharger. The trade is turbo lag: the moment between asking for power and the turbine spooling up to deliver it.
V engine: Two banks of cylinders set at an angle to each other, as in a V6, V8 or V12. Much shorter than an inline engine with the same number of cylinders, which is what makes big cylinder counts packageable.

drivetrain

All-wheel drive (AWD): Power goes to all four wheels, usually through a centre differential that lets the axles turn at different speeds. Transforms traction off the line and in the wet, at the cost of weight and drag.
CVT: A continuously variable transmission has no fixed gears at all — a belt runs between pulleys that change diameter, so the engine can sit at its most efficient speed. Efficient, but the disconnect between revs and road speed is what people describe as rubber-banding.
Differential: The gearset that splits drive between two wheels while letting them rotate at different speeds — necessary because the outside wheel travels further through a corner than the inside one.
Dual-clutch transmission (DCT): Two clutches, one holding the odd gears and one the even, so the next ratio is already engaged and waiting. Shifts land in milliseconds, which is why it displaced the manual in most performance cars.
Final drive ratio: The last gear reduction before the wheels. A shorter (numerically higher) final drive sharpens acceleration everywhere but caps top speed and raises cruising revs.
Front-wheel drive (FWD): The front wheels both steer and drive. Cheap to package and stable when it loses grip, but asking one pair of tyres to do two jobs limits how much power it can usefully take.
Limited-slip differential (LSD): A differential that restricts how much torque a spinning wheel can take from the one that still has grip. Without one, an open diff will happily send everything to the wheel in the air.
Rear-wheel drive (RWD): The rear wheels drive, the front wheels steer. Separating the jobs gives better weight transfer under acceleration and cleaner steering feel — the traditional sports car layout.
Torque converter: A fluid coupling that replaces the clutch in a traditional automatic, letting the engine idle while the car is stationary in gear. It also multiplies torque from a standstill, which is why autos launch smoothly.

performance figures

0-60 mph: Time from a standstill to 60 mph, the standard acceleration benchmark. Below about four seconds it's usually limited by traction rather than power, which is why all-wheel-drive cars post numbers their power alone wouldn't explain.
Downforce: Aerodynamic load pressing the car into the road, generated by wings, splitters and underbody shaping. It buys grip that rises with speed — but always at some cost in drag.
Drag coefficient (Cd): How cleanly a shape slips through air, independent of how big it is. Multiply it by frontal area for the number that actually determines top speed and motorway fuel consumption.
Horsepower: The rate of doing work — torque multiplied by engine speed. Power is what keeps a car pulling as speed rises, which is why top speed tracks power far more closely than torque.
Kerb weight: What the car weighs ready to drive, with fluids and a tank of fuel but nobody in it. Quoted weights vary by market and specification, so cross-brand comparisons are looser than they look.
Power-to-weight ratio: Power divided by mass, usually in bhp per tonne. It predicts how quick a car feels far better than horsepower alone — 200 bhp in a light car outruns 300 bhp in a heavy one.
Redline: The maximum engine speed the manufacturer considers safe, set by how fast the valvetrain and rotating assembly can be pushed before something lets go.
Top speed: Almost always limited by aerodynamic drag or by gearing rather than by running out of power — drag rises with the square of speed, so each extra mph per hour costs disproportionately more.
Torque: The twisting force the engine makes, quoted in lb-ft or Nm. Torque is how hard the car shoves you in the back; power is how long it can keep shoving as the speed climbs.

chassis and body

Anti-roll bar: A torsion bar tying the left and right suspension together so the car leans less in corners. Stiffening one end shifts the handling balance — more at the rear encourages the tail to rotate.
Body-on-frame: The body bolts onto a separate ladder chassis that carries the loads. Heavy and less rigid than a monocoque, but tough and easy to repair, which is why pickups and serious off-roaders still use it.
Double wishbone: Suspension using two A-shaped arms per wheel. It keeps the tyre more upright as the suspension moves than a strut does, so there's more rubber on the road mid-corner — at the cost of space and money.
MacPherson strut: A compact front suspension that combines the damper and the wheel's locating strut in one unit. Cheap, light and space-efficient, which is why it's on the front of most ordinary cars.
Monocoque (unibody): The body shell itself carries the structural loads rather than sitting on a separate frame. Lighter and far stiffer for its weight, and the basis of essentially every modern car.
Understeer and oversteer: Which end runs out of grip first. Understeer is the front washing wide of where you pointed it; oversteer is the rear stepping out. Road cars are deliberately set up to understeer, because it's the more recoverable of the two.
Unsprung mass: Everything not carried by the springs — wheels, tyres, brakes, and part of the suspension. Reducing it lets the wheel follow a bumpy surface more faithfully, which is why light wheels improve both ride and grip.
Wheelbase: The distance between the front and rear axle centres. Longer generally means a steadier car and more cabin space; shorter means it changes direction more eagerly.